Collection 结构及源码解析

超、凢脫俗 2022-05-12 08:18 261阅读 0赞

这个集合的超类，就是集合的祖宗，是个接口，只提供接口

![这里写图片描述][70]  
这个是关系

public interface Collection<E> extends Iterable<E> {
 
 /**
 * Returns the number of elements in this collection. If this collection
 * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
 * <tt>Integer.MAX_VALUE</tt>.
 *
 * @return the number of elements in this collection
 */
 int size();
 
 /**
 * Returns <tt>true</tt> if this collection contains no elements.
 *
 * @return <tt>true</tt> if this collection contains no elements
 */
 boolean isEmpty();
 
 /**
 * Returns <tt>true</tt> if this collection contains the specified element.
 * More formally, returns <tt>true</tt> if and only if this collection
 * contains at least one element <tt>e</tt> such that
 * <tt>(o==null ? e==null : o.equals(e))</tt>.
 *
 * @param o element whose presence in this collection is to be tested
 * @return <tt>true</tt> if this collection contains the specified
 * element
 * @throws ClassCastException if the type of the specified element
 * is incompatible with this collection
 * (<a href="#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified element is null and this
 * collection does not permit null elements
 * (<a href="#optional-restrictions">optional</a>)
 */
 boolean contains(Object o);
 
 /**
 * Returns an iterator over the elements in this collection. There are no
 * guarantees concerning the order in which the elements are returned
 * (unless this collection is an instance of some class that provides a
 * guarantee).
 *
 * @return an <tt>Iterator</tt> over the elements in this collection
 */
 Iterator<E> iterator();
 
 /**
 * Returns an array containing all of the elements in this collection.
 * If this collection makes any guarantees as to what order its elements
 * are returned by its iterator, this method must return the elements in
 * the same order.
 *
 * The returned array will be "safe" in that no references to it are
 * maintained by this collection. (In other words, this method must
 * allocate a new array even if this collection is backed by an array).
 * The caller is thus free to modify the returned array.
 *
 * This method acts as bridge between array-based and collection-based
 * APIs.
 *
 * @return an array containing all of the elements in this collection
 */
 Object[] toArray();
 
 /**
 * Returns an array containing all of the elements in this collection;
 * the runtime type of the returned array is that of the specified array.
 * If the collection fits in the specified array, it is returned therein.
 * Otherwise, a new array is allocated with the runtime type of the
 * specified array and the size of this collection.
 *
 * If this collection fits in the specified array with room to spare
 * (i.e., the array has more elements than this collection), the element
 * in the array immediately following the end of the collection is set to
 * <tt>null</tt>. (This is useful in determining the length of this
 * collection only if the caller knows that this collection does
 * not contain any <tt>null</tt> elements.)
 *
 * If this collection makes any guarantees as to what order its elements
 * are returned by its iterator, this method must return the elements in
 * the same order.
 *
 * Like the {@link #toArray()} method, this method acts as bridge between
 * array-based and collection-based APIs. Further, this method allows
 * precise control over the runtime type of the output array, and may,
 * under certain circumstances, be used to save allocation costs.
 *
 * Suppose <tt>x</tt> is a collection known to contain only strings.
 * The following code can be used to dump the collection into a newly
 * allocated array of <tt>String</tt>:
 *
 * <pre>
 * String[] y = x.toArray(new String[0]);</pre>
 *
 * Note that <tt>toArray(new Object[0])</tt> is identical in function to
 * <tt>toArray()</tt>.
 *
 * @param <T> the runtime type of the array to contain the collection
 * @param a the array into which the elements of this collection are to be
 * stored, if it is big enough; otherwise, a new array of the same
 * runtime type is allocated for this purpose.
 * @return an array containing all of the elements in this collection
 * @throws ArrayStoreException if the runtime type of the specified array
 * is not a supertype of the runtime type of every element in
 * this collection
 * @throws NullPointerException if the specified array is null
 */
 <T> T[] toArray(T[] a);
 
 // Modification Operations
 
 /**
 * Ensures that this collection contains the specified element (optional
 * operation). Returns <tt>true</tt> if this collection changed as a
 * result of the call. (Returns <tt>false</tt> if this collection does
 * not permit duplicates and already contains the specified element.)
 *
 * Collections that support this operation may place limitations on what
 * elements may be added to this collection. In particular, some
 * collections will refuse to add <tt>null</tt> elements, and others will
 * impose restrictions on the type of elements that may be added.
 * Collection classes should clearly specify in their documentation any
 * restrictions on what elements may be added.
 *
 * If a collection refuses to add a particular element for any reason
 * other than that it already contains the element, it must throw
 * an exception (rather than returning <tt>false</tt>). This preserves
 * the invariant that a collection always contains the specified element
 * after this call returns.
 *
 * @param e element whose presence in this collection is to be ensured
 * @return <tt>true</tt> if this collection changed as a result of the
 * call
 * @throws UnsupportedOperationException if the <tt>add</tt> operation
 * is not supported by this collection
 * @throws ClassCastException if the class of the specified element
 * prevents it from being added to this collection
 * @throws NullPointerException if the specified element is null and this
 * collection does not permit null elements
 * @throws IllegalArgumentException if some property of the element
 * prevents it from being added to this collection
 * @throws IllegalStateException if the element cannot be added at this
 * time due to insertion restrictions
 */
 boolean add(E e);
 
 /**
 * Removes a single instance of the specified element from this
 * collection, if it is present (optional operation). More formally,
 * removes an element <tt>e</tt> such that
 * <tt>(o==null ? e==null : o.equals(e))</tt>, if
 * this collection contains one or more such elements. Returns
 * <tt>true</tt> if this collection contained the specified element (or
 * equivalently, if this collection changed as a result of the call).
 *
 * @param o element to be removed from this collection, if present
 * @return <tt>true</tt> if an element was removed as a result of this call
 * @throws ClassCastException if the type of the specified element
 * is incompatible with this collection
 * (<a href="#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified element is null and this
 * collection does not permit null elements
 * (<a href="#optional-restrictions">optional</a>)
 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
 * is not supported by this collection
 */
 boolean remove(Object o);
 
 
 // Bulk Operations
 
 /**
 * Returns <tt>true</tt> if this collection contains all of the elements
 * in the specified collection.
 *
 * @param c collection to be checked for containment in this collection
 * @return <tt>true</tt> if this collection contains all of the elements
 * in the specified collection
 * @throws ClassCastException if the types of one or more elements
 * in the specified collection are incompatible with this
 * collection
 * (<a href="#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified collection contains one
 * or more null elements and this collection does not permit null
 * elements
 * (<a href="#optional-restrictions">optional</a>),
 * or if the specified collection is null.
 * @see #contains(Object)
 */
 boolean containsAll(Collection<?> c);
 
 /**
 * Adds all of the elements in the specified collection to this collection
 * (optional operation). The behavior of this operation is undefined if
 * the specified collection is modified while the operation is in progress.
 * (This implies that the behavior of this call is undefined if the
 * specified collection is this collection, and this collection is
 * nonempty.)
 *
 * @param c collection containing elements to be added to this collection
 * @return <tt>true</tt> if this collection changed as a result of the call
 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
 * is not supported by this collection
 * @throws ClassCastException if the class of an element of the specified
 * collection prevents it from being added to this collection
 * @throws NullPointerException if the specified collection contains a
 * null element and this collection does not permit null elements,
 * or if the specified collection is null
 * @throws IllegalArgumentException if some property of an element of the
 * specified collection prevents it from being added to this
 * collection
 * @throws IllegalStateException if not all the elements can be added at
 * this time due to insertion restrictions
 * @see #add(Object)
 */
 boolean addAll(Collection<? extends E> c);
 
 /**
 * Removes all of this collection's elements that are also contained in the
 * specified collection (optional operation). After this call returns,
 * this collection will contain no elements in common with the specified
 * collection.
 *
 * @param c collection containing elements to be removed from this collection
 * @return <tt>true</tt> if this collection changed as a result of the
 * call
 * @throws UnsupportedOperationException if the <tt>removeAll</tt> method
 * is not supported by this collection
 * @throws ClassCastException if the types of one or more elements
 * in this collection are incompatible with the specified
 * collection
 * (<a href="#optional-restrictions">optional</a>)
 * @throws NullPointerException if this collection contains one or more
 * null elements and the specified collection does not support
 * null elements
 * (<a href="#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 * @see #contains(Object)
 */
 boolean removeAll(Collection<?> c);
 
 /**
 * Removes all of the elements of this collection that satisfy the given
 * predicate. Errors or runtime exceptions thrown during iteration or by
 * the predicate are relayed to the caller.
 *
 * @implSpec
 * The default implementation traverses all elements of the collection using
 * its {@link #iterator}. Each matching element is removed using
 * {@link Iterator#remove()}. If the collection's iterator does not
 * support removal then an {@code UnsupportedOperationException} will be
 * thrown on the first matching element.
 *
 * @param filter a predicate which returns {@code true} for elements to be
 * removed
 * @return {@code true} if any elements were removed
 * @throws NullPointerException if the specified filter is null
 * @throws UnsupportedOperationException if elements cannot be removed
 * from this collection. Implementations may throw this exception if a
 * matching element cannot be removed or if, in general, removal is not
 * supported.
 * @since 1.8
 */
 default boolean removeIf(Predicate<? super E> filter) {
 Objects.requireNonNull(filter);
 boolean removed = false;
 final Iterator<E> each = iterator();
 while (each.hasNext()) {
 if (filter.test(each.next())) {
 each.remove();
 removed = true;
 }
 }
 return removed;
 }
 
 /**
 * Retains only the elements in this collection that are contained in the
 * specified collection (optional operation). In other words, removes from
 * this collection all of its elements that are not contained in the
 * specified collection.
 *
 * @param c collection containing elements to be retained in this collection
 * @return <tt>true</tt> if this collection changed as a result of the call
 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
 * is not supported by this collection
 * @throws ClassCastException if the types of one or more elements
 * in this collection are incompatible with the specified
 * collection
 * (<a href="#optional-restrictions">optional</a>)
 * @throws NullPointerException if this collection contains one or more
 * null elements and the specified collection does not permit null
 * elements
 * (<a href="#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 * @see #contains(Object)
 */
 boolean retainAll(Collection<?> c);
 
 /**
 * Removes all of the elements from this collection (optional operation).
 * The collection will be empty after this method returns.
 *
 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
 * is not supported by this collection
 */
 void clear();
 
 
 // Comparison and hashing
 
 /**
 * Compares the specified object with this collection for equality. 
 *
 * While the <tt>Collection</tt> interface adds no stipulations to the
 * general contract for the <tt>Object.equals</tt>, programmers who
 * implement the <tt>Collection</tt> interface "directly" (in other words,
 * create a class that is a <tt>Collection</tt> but is not a <tt>Set</tt>
 * or a <tt>List</tt>) must exercise care if they choose to override the
 * <tt>Object.equals</tt>. It is not necessary to do so, and the simplest
 * course of action is to rely on <tt>Object</tt>'s implementation, but
 * the implementor may wish to implement a "value comparison" in place of
 * the default "reference comparison." (The <tt>List</tt> and
 * <tt>Set</tt> interfaces mandate such value comparisons.)
 *
 * The general contract for the <tt>Object.equals</tt> method states that
 * equals must be symmetric (in other words, <tt>a.equals(b)</tt> if and
 * only if <tt>b.equals(a)</tt>). The contracts for <tt>List.equals</tt>
 * and <tt>Set.equals</tt> state that lists are only equal to other lists,
 * and sets to other sets. Thus, a custom <tt>equals</tt> method for a
 * collection class that implements neither the <tt>List</tt> nor
 * <tt>Set</tt> interface must return <tt>false</tt> when this collection
 * is compared to any list or set. (By the same logic, it is not possible
 * to write a class that correctly implements both the <tt>Set</tt> and
 * <tt>List</tt> interfaces.)
 *
 * @param o object to be compared for equality with this collection
 * @return <tt>true</tt> if the specified object is equal to this
 * collection
 *
 * @see Object#equals(Object)
 * @see Set#equals(Object)
 * @see List#equals(Object)
 */
 boolean equals(Object o);
 
 /**
 * Returns the hash code value for this collection. While the
 * <tt>Collection</tt> interface adds no stipulations to the general
 * contract for the <tt>Object.hashCode</tt> method, programmers should
 * take note that any class that overrides the <tt>Object.equals</tt>
 * method must also override the <tt>Object.hashCode</tt> method in order
 * to satisfy the general contract for the <tt>Object.hashCode</tt> method.
 * In particular, <tt>c1.equals(c2)</tt> implies that
 * <tt>c1.hashCode()==c2.hashCode()</tt>.
 *
 * @return the hash code value for this collection
 *
 * @see Object#hashCode()
 * @see Object#equals(Object)
 */
 int hashCode();
 
 /**
 * Creates a {@link Spliterator} over the elements in this collection.
 *
 * Implementations should document characteristic values reported by the
 * spliterator. Such characteristic values are not required to be reported
 * if the spliterator reports {@link Spliterator#SIZED} and this collection
 * contains no elements.
 *
 * The default implementation should be overridden by subclasses that
 * can return a more efficient spliterator. In order to
 * preserve expected laziness behavior for the {@link #stream()} and
 * {@link #parallelStream()}} methods, spliterators should either have the
 * characteristic of {@code IMMUTABLE} or {@code CONCURRENT}, or be
 * <a href="Spliterator.html#binding">late-binding</a>.
 * If none of these is practical, the overriding class should describe the
 * spliterator's documented policy of binding and structural interference,
 * and should override the {@link #stream()} and {@link #parallelStream()}
 * methods to create streams using a {@code Supplier} of the spliterator,
 * as in:
 * <pre>{@code
 * Stream<E> s = StreamSupport.stream(() -> spliterator(), spliteratorCharacteristics)
 * }</pre>
 * These requirements ensure that streams produced by the
 * {@link #stream()} and {@link #parallelStream()} methods will reflect the
 * contents of the collection as of initiation of the terminal stream
 * operation.
 *
 * @implSpec
 * The default implementation creates a
 * <a href="Spliterator.html#binding">late-binding</a> spliterator
 * from the collections's {@code Iterator}. The spliterator inherits the
 * fail-fast properties of the collection's iterator.
 * 
 * The created {@code Spliterator} reports {@link Spliterator#SIZED}.
 *
 * @implNote
 * The created {@code Spliterator} additionally reports
 * {@link Spliterator#SUBSIZED}.
 *
 * If a spliterator covers no elements then the reporting of additional
 * characteristic values, beyond that of {@code SIZED} and {@code SUBSIZED},
 * does not aid clients to control, specialize or simplify computation.
 * However, this does enable shared use of an immutable and empty
 * spliterator instance (see {@link Spliterators#emptySpliterator()}) for
 * empty collections, and enables clients to determine if such a spliterator
 * covers no elements.
 *
 * @return a {@code Spliterator} over the elements in this collection
 * @since 1.8
 */
 @Override
 default Spliterator<E> spliterator() {
 return Spliterators.spliterator(this, 0);
 }
 
 /**
 * Returns a sequential {@code Stream} with this collection as its source.
 *
 * This method should be overridden when the {@link #spliterator()}
 * method cannot return a spliterator that is {@code IMMUTABLE},
 * {@code CONCURRENT}, or late-binding. (See {@link #spliterator()}
 * for details.)
 *
 * @implSpec
 * The default implementation creates a sequential {@code Stream} from the
 * collection's {@code Spliterator}.
 *
 * @return a sequential {@code Stream} over the elements in this collection
 * @since 1.8
 */
 default Stream<E> stream() {
 return StreamSupport.stream(spliterator(), false);
 }
 
 /**
 * Returns a possibly parallel {@code Stream} with this collection as its
 * source. It is allowable for this method to return a sequential stream.
 *
 * This method should be overridden when the {@link #spliterator()}
 * method cannot return a spliterator that is {@code IMMUTABLE},
 * {@code CONCURRENT}, or late-binding. (See {@link #spliterator()}
 * for details.)
 *
 * @implSpec
 * The default implementation creates a parallel {@code Stream} from the
 * collection's {@code Spliterator}.
 *
 * @return a possibly parallel {@code Stream} over the elements in this
 * collection
 * @since 1.8
 */
 default Stream<E> parallelStream() {
 return StreamSupport.stream(spliterator(), true);
 }
 }

这个是接口，它的实现呐在这里AbstractCollection

public abstract class AbstractCollection<E> implements Collection<E> {
 /**
 * Sole constructor. (For invocation by subclass constructors, typically
 * implicit.)
 */
 protected AbstractCollection() {
 }
 
 // Query Operations
 
 /**
 * Returns an iterator over the elements contained in this collection.
 *
 * @return an iterator over the elements contained in this collection
 */
 public abstract Iterator<E> iterator();
 
 public abstract int size();
 
 /**
 * {@inheritDoc}
 *
 * This implementation returns <tt>size() == 0</tt>.
 */
 public boolean isEmpty() {
 return size() == 0;
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation iterates over the elements in the collection,
 * checking each element in turn for equality with the specified element.
 *
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public boolean contains(Object o) {
 Iterator<E> it = iterator();
 if (o==null) {
 while (it.hasNext())
 if (it.next()==null)
 return true;
 } else {
 while (it.hasNext())
 if (o.equals(it.next()))
 return true;
 }
 return false;
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation returns an array containing all the elements
 * returned by this collection's iterator, in the same order, stored in
 * consecutive elements of the array, starting with index {@code 0}.
 * The length of the returned array is equal to the number of elements
 * returned by the iterator, even if the size of this collection changes
 * during iteration, as might happen if the collection permits
 * concurrent modification during iteration. The {@code size} method is
 * called only as an optimization hint; the correct result is returned
 * even if the iterator returns a different number of elements.
 *
 * This method is equivalent to:
 *
 * <pre> {@code
 * List<E> list = new ArrayList<E>(size());
 * for (E e : this)
 * list.add(e);
 * return list.toArray();
 * }</pre>
 */
 public Object[] toArray() {
 // Estimate size of array; be prepared to see more or fewer elements
 Object[] r = new Object[size()];
 Iterator<E> it = iterator();
 for (int i = 0; i < r.length; i++) {
 if (! it.hasNext()) // fewer elements than expected
 return Arrays.copyOf(r, i);
 r[i] = it.next();
 }
 return it.hasNext() ? finishToArray(r, it) : r;
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation returns an array containing all the elements
 * returned by this collection's iterator in the same order, stored in
 * consecutive elements of the array, starting with index {@code 0}.
 * If the number of elements returned by the iterator is too large to
 * fit into the specified array, then the elements are returned in a
 * newly allocated array with length equal to the number of elements
 * returned by the iterator, even if the size of this collection
 * changes during iteration, as might happen if the collection permits
 * concurrent modification during iteration. The {@code size} method is
 * called only as an optimization hint; the correct result is returned
 * even if the iterator returns a different number of elements.
 *
 * This method is equivalent to:
 *
 * <pre> {@code
 * List<E> list = new ArrayList<E>(size());
 * for (E e : this)
 * list.add(e);
 * return list.toArray(a);
 * }</pre>
 *
 * @throws ArrayStoreException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 @SuppressWarnings("unchecked")
 public <T> T[] toArray(T[] a) {
 // Estimate size of array; be prepared to see more or fewer elements
 int size = size();
 T[] r = a.length >= size ? a :
 (T[])java.lang.reflect.Array
 .newInstance(a.getClass().getComponentType(), size);
 Iterator<E> it = iterator();
 
 for (int i = 0; i < r.length; i++) {
 if (! it.hasNext()) { // fewer elements than expected
 if (a == r) {
 r[i] = null; // null-terminate
 } else if (a.length < i) {
 return Arrays.copyOf(r, i);
 } else {
 System.arraycopy(r, 0, a, 0, i);
 if (a.length > i) {
 a[i] = null;
 }
 }
 return a;
 }
 r[i] = (T)it.next();
 }
 // more elements than expected
 return it.hasNext() ? finishToArray(r, it) : r;
 }
 
 /**
 * The maximum size of array to allocate.
 * Some VMs reserve some header words in an array.
 * Attempts to allocate larger arrays may result in
 * OutOfMemoryError: Requested array size exceeds VM limit
 */
 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
 
 /**
 * Reallocates the array being used within toArray when the iterator
 * returned more elements than expected, and finishes filling it from
 * the iterator.
 *
 * @param r the array, replete with previously stored elements
 * @param it the in-progress iterator over this collection
 * @return array containing the elements in the given array, plus any
 * further elements returned by the iterator, trimmed to size
 */
 @SuppressWarnings("unchecked")
 private static <T> T[] finishToArray(T[] r, Iterator<?> it) {
 int i = r.length;
 while (it.hasNext()) {
 int cap = r.length;
 if (i == cap) {
 int newCap = cap + (cap >> 1) + 1;
 // overflow-conscious code
 if (newCap - MAX_ARRAY_SIZE > 0)
 newCap = hugeCapacity(cap + 1);
 r = Arrays.copyOf(r, newCap);
 }
 r[i++] = (T)it.next();
 }
 // trim if overallocated
 return (i == r.length) ? r : Arrays.copyOf(r, i);
 }
 
 private static int hugeCapacity(int minCapacity) {
 if (minCapacity < 0) // overflow
 throw new OutOfMemoryError
 ("Required array size too large");
 return (minCapacity > MAX_ARRAY_SIZE) ?
 Integer.MAX_VALUE :
 MAX_ARRAY_SIZE;
 }
 
 // Modification Operations
 
 /**
 * {@inheritDoc}
 *
 * This implementation always throws an
 * <tt>UnsupportedOperationException</tt>.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 * @throws IllegalStateException {@inheritDoc}
 */
 public boolean add(E e) {
 throw new UnsupportedOperationException();
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation iterates over the collection looking for the
 * specified element. If it finds the element, it removes the element
 * from the collection using the iterator's remove method.
 *
 * Note that this implementation throws an
 * <tt>UnsupportedOperationException</tt> if the iterator returned by this
 * collection's iterator method does not implement the <tt>remove</tt>
 * method and this collection contains the specified object.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public boolean remove(Object o) {
 Iterator<E> it = iterator();
 if (o==null) {
 while (it.hasNext()) {
 if (it.next()==null) {
 it.remove();
 return true;
 }
 }
 } else {
 while (it.hasNext()) {
 if (o.equals(it.next())) {
 it.remove();
 return true;
 }
 }
 }
 return false;
 }
 
 
 // Bulk Operations
 
 /**
 * {@inheritDoc}
 *
 * This implementation iterates over the specified collection,
 * checking each element returned by the iterator in turn to see
 * if it's contained in this collection. If all elements are so
 * contained <tt>true</tt> is returned, otherwise <tt>false</tt>.
 *
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 * @see #contains(Object)
 */
 public boolean containsAll(Collection<?> c) {
 for (Object e : c)
 if (!contains(e))
 return false;
 return true;
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation iterates over the specified collection, and adds
 * each object returned by the iterator to this collection, in turn.
 *
 * Note that this implementation will throw an
 * <tt>UnsupportedOperationException</tt> unless <tt>add</tt> is
 * overridden (assuming the specified collection is non-empty).
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 * @throws IllegalStateException {@inheritDoc}
 *
 * @see #add(Object)
 */
 public boolean addAll(Collection<? extends E> c) {
 boolean modified = false;
 for (E e : c)
 if (add(e))
 modified = true;
 return modified;
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation iterates over this collection, checking each
 * element returned by the iterator in turn to see if it's contained
 * in the specified collection. If it's so contained, it's removed from
 * this collection with the iterator's <tt>remove</tt> method.
 *
 * Note that this implementation will throw an
 * <tt>UnsupportedOperationException</tt> if the iterator returned by the
 * <tt>iterator</tt> method does not implement the <tt>remove</tt> method
 * and this collection contains one or more elements in common with the
 * specified collection.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 *
 * @see #remove(Object)
 * @see #contains(Object)
 */
 public boolean removeAll(Collection<?> c) {
 Objects.requireNonNull(c);
 boolean modified = false;
 Iterator<?> it = iterator();
 while (it.hasNext()) {
 if (c.contains(it.next())) {
 it.remove();
 modified = true;
 }
 }
 return modified;
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation iterates over this collection, checking each
 * element returned by the iterator in turn to see if it's contained
 * in the specified collection. If it's not so contained, it's removed
 * from this collection with the iterator's <tt>remove</tt> method.
 *
 * Note that this implementation will throw an
 * <tt>UnsupportedOperationException</tt> if the iterator returned by the
 * <tt>iterator</tt> method does not implement the <tt>remove</tt> method
 * and this collection contains one or more elements not present in the
 * specified collection.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 *
 * @see #remove(Object)
 * @see #contains(Object)
 */
 public boolean retainAll(Collection<?> c) {
 Objects.requireNonNull(c);
 boolean modified = false;
 Iterator<E> it = iterator();
 while (it.hasNext()) {
 if (!c.contains(it.next())) {
 it.remove();
 modified = true;
 }
 }
 return modified;
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation iterates over this collection, removing each
 * element using the <tt>Iterator.remove</tt> operation. Most
 * implementations will probably choose to override this method for
 * efficiency.
 *
 * Note that this implementation will throw an
 * <tt>UnsupportedOperationException</tt> if the iterator returned by this
 * collection's <tt>iterator</tt> method does not implement the
 * <tt>remove</tt> method and this collection is non-empty.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 */
 public void clear() {
 Iterator<E> it = iterator();
 while (it.hasNext()) {
 it.next();
 it.remove();
 }
 }
 
 
 // String conversion
 
 /**
 * Returns a string representation of this collection. The string
 * representation consists of a list of the collection's elements in the
 * order they are returned by its iterator, enclosed in square brackets
 * (<tt>"[]"</tt>). Adjacent elements are separated by the characters
 * <tt>", "</tt> (comma and space). Elements are converted to strings as
 * by {@link String#valueOf(Object)}.
 *
 * @return a string representation of this collection
 */
 public String toString() {
 Iterator<E> it = iterator();
 if (! it.hasNext())
 return "[]";
 
 StringBuilder sb = new StringBuilder();
 sb.append('[');
 for (;;) {
 E e = it.next();
 sb.append(e == this ? "(this Collection)" : e);
 if (! it.hasNext())
 return sb.append(']').toString();
 sb.append(',').append(' ');
 }
 }
 
 }

再来看一下List的源码

public interface List<E> extends Collection<E> {
 // Query Operations
 
 /**
 * Returns the number of elements in this list. If this list contains
 * more than <tt>Integer.MAX_VALUE</tt> elements, returns
 * <tt>Integer.MAX_VALUE</tt>.
 *
 * @return the number of elements in this list
 */
 int size();
 
 /**
 * Returns <tt>true</tt> if this list contains no elements.
 *
 * @return <tt>true</tt> if this list contains no elements
 */
 boolean isEmpty();
 
 /**
 * Returns <tt>true</tt> if this list contains the specified element.
 * More formally, returns <tt>true</tt> if and only if this list contains
 * at least one element <tt>e</tt> such that
 * <tt>(o==null ? e==null : o.equals(e))</tt>.
 *
 * @param o element whose presence in this list is to be tested
 * @return <tt>true</tt> if this list contains the specified element
 * @throws ClassCastException if the type of the specified element
 * is incompatible with this list
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified element is null and this
 * list does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 */
 boolean contains(Object o);
 
 /**
 * Returns an iterator over the elements in this list in proper sequence.
 *
 * @return an iterator over the elements in this list in proper sequence
 */
 Iterator<E> iterator();
 
 /**
 * Returns an array containing all of the elements in this list in proper
 * sequence (from first to last element).
 *
 * The returned array will be "safe" in that no references to it are
 * maintained by this list. (In other words, this method must
 * allocate a new array even if this list is backed by an array).
 * The caller is thus free to modify the returned array.
 *
 * This method acts as bridge between array-based and collection-based
 * APIs.
 *
 * @return an array containing all of the elements in this list in proper
 * sequence
 * @see Arrays#asList(Object[])
 */
 Object[] toArray();
 
 /**
 * Returns an array containing all of the elements in this list in
 * proper sequence (from first to last element); the runtime type of
 * the returned array is that of the specified array. If the list fits
 * in the specified array, it is returned therein. Otherwise, a new
 * array is allocated with the runtime type of the specified array and
 * the size of this list.
 *
 * If the list fits in the specified array with room to spare (i.e.,
 * the array has more elements than the list), the element in the array
 * immediately following the end of the list is set to <tt>null</tt>.
 * (This is useful in determining the length of the list only if
 * the caller knows that the list does not contain any null elements.)
 *
 * Like the {@link #toArray()} method, this method acts as bridge between
 * array-based and collection-based APIs. Further, this method allows
 * precise control over the runtime type of the output array, and may,
 * under certain circumstances, be used to save allocation costs.
 *
 * Suppose <tt>x</tt> is a list known to contain only strings.
 * The following code can be used to dump the list into a newly
 * allocated array of <tt>String</tt>:
 *
 * <pre>{@code
 * String[] y = x.toArray(new String[0]);
 * }</pre>
 *
 * Note that <tt>toArray(new Object[0])</tt> is identical in function to
 * <tt>toArray()</tt>.
 *
 * @param a the array into which the elements of this list are to
 * be stored, if it is big enough; otherwise, a new array of the
 * same runtime type is allocated for this purpose.
 * @return an array containing the elements of this list
 * @throws ArrayStoreException if the runtime type of the specified array
 * is not a supertype of the runtime type of every element in
 * this list
 * @throws NullPointerException if the specified array is null
 */
 <T> T[] toArray(T[] a);
 
 
 // Modification Operations
 
 /**
 * Appends the specified element to the end of this list (optional
 * operation).
 *
 * Lists that support this operation may place limitations on what
 * elements may be added to this list. In particular, some
 * lists will refuse to add null elements, and others will impose
 * restrictions on the type of elements that may be added. List
 * classes should clearly specify in their documentation any restrictions
 * on what elements may be added.
 *
 * @param e element to be appended to this list
 * @return <tt>true</tt> (as specified by {@link Collection#add})
 * @throws UnsupportedOperationException if the <tt>add</tt> operation
 * is not supported by this list
 * @throws ClassCastException if the class of the specified element
 * prevents it from being added to this list
 * @throws NullPointerException if the specified element is null and this
 * list does not permit null elements
 * @throws IllegalArgumentException if some property of this element
 * prevents it from being added to this list
 */
 boolean add(E e);
 
 /**
 * Removes the first occurrence of the specified element from this list,
 * if it is present (optional operation). If this list does not contain
 * the element, it is unchanged. More formally, removes the element with
 * the lowest index <tt>i</tt> such that
 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
 * (if such an element exists). Returns <tt>true</tt> if this list
 * contained the specified element (or equivalently, if this list changed
 * as a result of the call).
 *
 * @param o element to be removed from this list, if present
 * @return <tt>true</tt> if this list contained the specified element
 * @throws ClassCastException if the type of the specified element
 * is incompatible with this list
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified element is null and this
 * list does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
 * is not supported by this list
 */
 boolean remove(Object o);
 
 
 // Bulk Modification Operations
 
 /**
 * Returns <tt>true</tt> if this list contains all of the elements of the
 * specified collection.
 *
 * @param c collection to be checked for containment in this list
 * @return <tt>true</tt> if this list contains all of the elements of the
 * specified collection
 * @throws ClassCastException if the types of one or more elements
 * in the specified collection are incompatible with this
 * list
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified collection contains one
 * or more null elements and this list does not permit null
 * elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #contains(Object)
 */
 boolean containsAll(Collection<?> c);
 
 /**
 * Appends all of the elements in the specified collection to the end of
 * this list, in the order that they are returned by the specified
 * collection's iterator (optional operation). The behavior of this
 * operation is undefined if the specified collection is modified while
 * the operation is in progress. (Note that this will occur if the
 * specified collection is this list, and it's nonempty.)
 *
 * @param c collection containing elements to be added to this list
 * @return <tt>true</tt> if this list changed as a result of the call
 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
 * is not supported by this list
 * @throws ClassCastException if the class of an element of the specified
 * collection prevents it from being added to this list
 * @throws NullPointerException if the specified collection contains one
 * or more null elements and this list does not permit null
 * elements, or if the specified collection is null
 * @throws IllegalArgumentException if some property of an element of the
 * specified collection prevents it from being added to this list
 * @see #add(Object)
 */
 boolean addAll(Collection<? extends E> c);
 
 /**
 * Inserts all of the elements in the specified collection into this
 * list at the specified position (optional operation). Shifts the
 * element currently at that position (if any) and any subsequent
 * elements to the right (increases their indices). The new elements
 * will appear in this list in the order that they are returned by the
 * specified collection's iterator. The behavior of this operation is
 * undefined if the specified collection is modified while the
 * operation is in progress. (Note that this will occur if the specified
 * collection is this list, and it's nonempty.)
 *
 * @param index index at which to insert the first element from the
 * specified collection
 * @param c collection containing elements to be added to this list
 * @return <tt>true</tt> if this list changed as a result of the call
 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
 * is not supported by this list
 * @throws ClassCastException if the class of an element of the specified
 * collection prevents it from being added to this list
 * @throws NullPointerException if the specified collection contains one
 * or more null elements and this list does not permit null
 * elements, or if the specified collection is null
 * @throws IllegalArgumentException if some property of an element of the
 * specified collection prevents it from being added to this list
 * @throws IndexOutOfBoundsException if the index is out of range
 * (<tt>index < 0 || index > size()</tt>)
 */
 boolean addAll(int index, Collection<? extends E> c);
 
 /**
 * Removes from this list all of its elements that are contained in the
 * specified collection (optional operation).
 *
 * @param c collection containing elements to be removed from this list
 * @return <tt>true</tt> if this list changed as a result of the call
 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
 * is not supported by this list
 * @throws ClassCastException if the class of an element of this list
 * is incompatible with the specified collection
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this list contains a null element and the
 * specified collection does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 * @see #contains(Object)
 */
 boolean removeAll(Collection<?> c);
 
 /**
 * Retains only the elements in this list that are contained in the
 * specified collection (optional operation). In other words, removes
 * from this list all of its elements that are not contained in the
 * specified collection.
 *
 * @param c collection containing elements to be retained in this list
 * @return <tt>true</tt> if this list changed as a result of the call
 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
 * is not supported by this list
 * @throws ClassCastException if the class of an element of this list
 * is incompatible with the specified collection
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this list contains a null element and the
 * specified collection does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 * @see #contains(Object)
 */
 boolean retainAll(Collection<?> c);
 
 /**
 * Replaces each element of this list with the result of applying the
 * operator to that element. Errors or runtime exceptions thrown by
 * the operator are relayed to the caller.
 *
 * @implSpec
 * The default implementation is equivalent to, for this {@code list}:
 * <pre>{@code
 * final ListIterator<E> li = list.listIterator();
 * while (li.hasNext()) {
 * li.set(operator.apply(li.next()));
 * }
 * }</pre>
 *
 * If the list's list-iterator does not support the {@code set} operation
 * then an {@code UnsupportedOperationException} will be thrown when
 * replacing the first element.
 *
 * @param operator the operator to apply to each element
 * @throws UnsupportedOperationException if this list is unmodifiable.
 * Implementations may throw this exception if an element
 * cannot be replaced or if, in general, modification is not
 * supported
 * @throws NullPointerException if the specified operator is null or
 * if the operator result is a null value and this list does
 * not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @since 1.8
 */
 default void replaceAll(UnaryOperator<E> operator) {
 Objects.requireNonNull(operator);
 final ListIterator<E> li = this.listIterator();
 while (li.hasNext()) {
 li.set(operator.apply(li.next()));
 }
 }
 
 /**
 * Sorts this list according to the order induced by the specified
 * {@link Comparator}.
 *
 * All elements in this list must be mutually comparable using the
 * specified comparator (that is, {@code c.compare(e1, e2)} must not throw
 * a {@code ClassCastException} for any elements {@code e1} and {@code e2}
 * in the list).
 *
 * If the specified comparator is {@code null} then all elements in this
 * list must implement the {@link Comparable} interface and the elements'
 * {@linkplain Comparable natural ordering} should be used.
 *
 * This list must be modifiable, but need not be resizable.
 *
 * @implSpec
 * The default implementation obtains an array containing all elements in
 * this list, sorts the array, and iterates over this list resetting each
 * element from the corresponding position in the array. (This avoids the
 * n2 log(n) performance that would result from attempting
 * to sort a linked list in place.)
 *
 * @implNote
 * This implementation is a stable, adaptive, iterative mergesort that
 * requires far fewer than n lg(n) comparisons when the input array is
 * partially sorted, while offering the performance of a traditional
 * mergesort when the input array is randomly ordered. If the input array
 * is nearly sorted, the implementation requires approximately n
 * comparisons. Temporary storage requirements vary from a small constant
 * for nearly sorted input arrays to n/2 object references for randomly
 * ordered input arrays.
 *
 * The implementation takes equal advantage of ascending and
 * descending order in its input array, and can take advantage of
 * ascending and descending order in different parts of the same
 * input array. It is well-suited to merging two or more sorted arrays:
 * simply concatenate the arrays and sort the resulting array.
 *
 * The implementation was adapted from Tim Peters's list sort for Python
 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
 * TimSort</a>). It uses techniques from Peter McIlroy's "Optimistic
 * Sorting and Information Theoretic Complexity", in Proceedings of the
 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
 * January 1993.
 *
 * @param c the {@code Comparator} used to compare list elements.
 * A {@code null} value indicates that the elements'
 * {@linkplain Comparable natural ordering} should be used
 * @throws ClassCastException if the list contains elements that are not
 * mutually comparable using the specified comparator
 * @throws UnsupportedOperationException if the list's list-iterator does
 * not support the {@code set} operation
 * @throws IllegalArgumentException
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * if the comparator is found to violate the {@link Comparator}
 * contract
 * @since 1.8
 */
 @SuppressWarnings({"unchecked", "rawtypes"})
 default void sort(Comparator<? super E> c) {
 Object[] a = this.toArray();
 Arrays.sort(a, (Comparator) c);
 ListIterator<E> i = this.listIterator();
 for (Object e : a) {
 i.next();
 i.set((E) e);
 }
 }
 
 /**
 * Removes all of the elements from this list (optional operation).
 * The list will be empty after this call returns.
 *
 * @throws UnsupportedOperationException if the <tt>clear</tt> operation
 * is not supported by this list
 */
 void clear();
 
 
 // Comparison and hashing
 
 /**
 * Compares the specified object with this list for equality. Returns
 * <tt>true</tt> if and only if the specified object is also a list, both
 * lists have the same size, and all corresponding pairs of elements in
 * the two lists are equal. (Two elements <tt>e1</tt> and
 * <tt>e2</tt> are equal if <tt>(e1==null ? e2==null :
 * e1.equals(e2))</tt>.) In other words, two lists are defined to be
 * equal if they contain the same elements in the same order. This
 * definition ensures that the equals method works properly across
 * different implementations of the <tt>List</tt> interface.
 *
 * @param o the object to be compared for equality with this list
 * @return <tt>true</tt> if the specified object is equal to this list
 */
 boolean equals(Object o);
 
 /**
 * Returns the hash code value for this list. The hash code of a list
 * is defined to be the result of the following calculation:
 * <pre>{@code
 * int hashCode = 1;
 * for (E e : list)
 * hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
 * }</pre>
 * This ensures that <tt>list1.equals(list2)</tt> implies that
 * <tt>list1.hashCode()==list2.hashCode()</tt> for any two lists,
 * <tt>list1</tt> and <tt>list2</tt>, as required by the general
 * contract of {@link Object#hashCode}.
 *
 * @return the hash code value for this list
 * @see Object#equals(Object)
 * @see #equals(Object)
 */
 int hashCode();
 
 
 // Positional Access Operations
 
 /**
 * Returns the element at the specified position in this list.
 *
 * @param index index of the element to return
 * @return the element at the specified position in this list
 * @throws IndexOutOfBoundsException if the index is out of range
 * (<tt>index < 0 || index >= size()</tt>)
 */
 E get(int index);
 
 /**
 * Replaces the element at the specified position in this list with the
 * specified element (optional operation).
 *
 * @param index index of the element to replace
 * @param element element to be stored at the specified position
 * @return the element previously at the specified position
 * @throws UnsupportedOperationException if the <tt>set</tt> operation
 * is not supported by this list
 * @throws ClassCastException if the class of the specified element
 * prevents it from being added to this list
 * @throws NullPointerException if the specified element is null and
 * this list does not permit null elements
 * @throws IllegalArgumentException if some property of the specified
 * element prevents it from being added to this list
 * @throws IndexOutOfBoundsException if the index is out of range
 * (<tt>index < 0 || index >= size()</tt>)
 */
 E set(int index, E element);
 
 /**
 * Inserts the specified element at the specified position in this list
 * (optional operation). Shifts the element currently at that position
 * (if any) and any subsequent elements to the right (adds one to their
 * indices).
 *
 * @param index index at which the specified element is to be inserted
 * @param element element to be inserted
 * @throws UnsupportedOperationException if the <tt>add</tt> operation
 * is not supported by this list
 * @throws ClassCastException if the class of the specified element
 * prevents it from being added to this list
 * @throws NullPointerException if the specified element is null and
 * this list does not permit null elements
 * @throws IllegalArgumentException if some property of the specified
 * element prevents it from being added to this list
 * @throws IndexOutOfBoundsException if the index is out of range
 * (<tt>index < 0 || index > size()</tt>)
 */
 void add(int index, E element);
 
 /**
 * Removes the element at the specified position in this list (optional
 * operation). Shifts any subsequent elements to the left (subtracts one
 * from their indices). Returns the element that was removed from the
 * list.
 *
 * @param index the index of the element to be removed
 * @return the element previously at the specified position
 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
 * is not supported by this list
 * @throws IndexOutOfBoundsException if the index is out of range
 * (<tt>index < 0 || index >= size()</tt>)
 */
 E remove(int index);
 
 
 // Search Operations
 
 /**
 * Returns the index of the first occurrence of the specified element
 * in this list, or -1 if this list does not contain the element.
 * More formally, returns the lowest index <tt>i</tt> such that
 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
 * or -1 if there is no such index.
 *
 * @param o element to search for
 * @return the index of the first occurrence of the specified element in
 * this list, or -1 if this list does not contain the element
 * @throws ClassCastException if the type of the specified element
 * is incompatible with this list
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified element is null and this
 * list does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 */
 int indexOf(Object o);
 
 /**
 * Returns the index of the last occurrence of the specified element
 * in this list, or -1 if this list does not contain the element.
 * More formally, returns the highest index <tt>i</tt> such that
 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
 * or -1 if there is no such index.
 *
 * @param o element to search for
 * @return the index of the last occurrence of the specified element in
 * this list, or -1 if this list does not contain the element
 * @throws ClassCastException if the type of the specified element
 * is incompatible with this list
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified element is null and this
 * list does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 */
 int lastIndexOf(Object o);
 
 
 // List Iterators
 
 /**
 * Returns a list iterator over the elements in this list (in proper
 * sequence).
 *
 * @return a list iterator over the elements in this list (in proper
 * sequence)
 */
 ListIterator<E> listIterator();
 
 /**
 * Returns a list iterator over the elements in this list (in proper
 * sequence), starting at the specified position in the list.
 * The specified index indicates the first element that would be
 * returned by an initial call to {@link ListIterator#next next}.
 * An initial call to {@link ListIterator#previous previous} would
 * return the element with the specified index minus one.
 *
 * @param index index of the first element to be returned from the
 * list iterator (by a call to {@link ListIterator#next next})
 * @return a list iterator over the elements in this list (in proper
 * sequence), starting at the specified position in the list
 * @throws IndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index > size()})
 */
 ListIterator<E> listIterator(int index);
 
 // View
 
 /**
 * Returns a view of the portion of this list between the specified
 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. (If
 * <tt>fromIndex</tt> and <tt>toIndex</tt> are equal, the returned list is
 * empty.) The returned list is backed by this list, so non-structural
 * changes in the returned list are reflected in this list, and vice-versa.
 * The returned list supports all of the optional list operations supported
 * by this list.
 *
 * This method eliminates the need for explicit range operations (of
 * the sort that commonly exist for arrays). Any operation that expects
 * a list can be used as a range operation by passing a subList view
 * instead of a whole list. For example, the following idiom
 * removes a range of elements from a list:
 * <pre>{@code
 * list.subList(from, to).clear();
 * }</pre>
 * Similar idioms may be constructed for <tt>indexOf</tt> and
 * <tt>lastIndexOf</tt>, and all of the algorithms in the
 * <tt>Collections</tt> class can be applied to a subList.
 *
 * The semantics of the list returned by this method become undefined if
 * the backing list (i.e., this list) is structurally modified in
 * any way other than via the returned list. (Structural modifications are
 * those that change the size of this list, or otherwise perturb it in such
 * a fashion that iterations in progress may yield incorrect results.)
 *
 * @param fromIndex low endpoint (inclusive) of the subList
 * @param toIndex high endpoint (exclusive) of the subList
 * @return a view of the specified range within this list
 * @throws IndexOutOfBoundsException for an illegal endpoint index value
 * (<tt>fromIndex < 0 || toIndex > size ||
 * fromIndex > toIndex</tt>)
 */
 List<E> subList(int fromIndex, int toIndex);
 
 /**
 * Creates a {@link Spliterator} over the elements in this list.
 *
 * The {@code Spliterator} reports {@link Spliterator#SIZED} and
 * {@link Spliterator#ORDERED}. Implementations should document the
 * reporting of additional characteristic values.
 *
 * @implSpec
 * The default implementation creates a
 * <a href="Spliterator.html#binding">late-binding</a> spliterator
 * from the list's {@code Iterator}. The spliterator inherits the
 * fail-fast properties of the list's iterator.
 *
 * @implNote
 * The created {@code Spliterator} additionally reports
 * {@link Spliterator#SUBSIZED}.
 *
 * @return a {@code Spliterator} over the elements in this list
 * @since 1.8
 */
 @Override
 default Spliterator<E> spliterator() {
 return Spliterators.spliterator(this, Spliterator.ORDERED);
 }
 }

然后看AbstractList这个源码

public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {
 /**
 * Sole constructor. (For invocation by subclass constructors, typically
 * implicit.)
 */
 protected AbstractList() {
 }
 
 /**
 * Appends the specified element to the end of this list (optional
 * operation).
 *
 * Lists that support this operation may place limitations on what
 * elements may be added to this list. In particular, some
 * lists will refuse to add null elements, and others will impose
 * restrictions on the type of elements that may be added. List
 * classes should clearly specify in their documentation any restrictions
 * on what elements may be added.
 *
 * This implementation calls {@code add(size(), e)}.
 *
 * Note that this implementation throws an
 * {@code UnsupportedOperationException} unless
 * {@link #add(int, Object) add(int, E)} is overridden.
 *
 * @param e element to be appended to this list
 * @return {@code true} (as specified by {@link Collection#add})
 * @throws UnsupportedOperationException if the {@code add} operation
 * is not supported by this list
 * @throws ClassCastException if the class of the specified element
 * prevents it from being added to this list
 * @throws NullPointerException if the specified element is null and this
 * list does not permit null elements
 * @throws IllegalArgumentException if some property of this element
 * prevents it from being added to this list
 */
 public boolean add(E e) {
 add(size(), e);
 return true;
 }
 
 /**
 * {@inheritDoc}
 *
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
 abstract public E get(int index);
 
 /**
 * {@inheritDoc}
 *
 * This implementation always throws an
 * {@code UnsupportedOperationException}.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
 public E set(int index, E element) {
 throw new UnsupportedOperationException();
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation always throws an
 * {@code UnsupportedOperationException}.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
 public void add(int index, E element) {
 throw new UnsupportedOperationException();
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation always throws an
 * {@code UnsupportedOperationException}.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
 public E remove(int index) {
 throw new UnsupportedOperationException();
 }
 
 
 // Search Operations
 
 /**
 * {@inheritDoc}
 *
 * This implementation first gets a list iterator (with
 * {@code listIterator()}). Then, it iterates over the list until the
 * specified element is found or the end of the list is reached.
 *
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public int indexOf(Object o) {
 ListIterator<E> it = listIterator();
 if (o==null) {
 while (it.hasNext())
 if (it.next()==null)
 return it.previousIndex();
 } else {
 while (it.hasNext())
 if (o.equals(it.next()))
 return it.previousIndex();
 }
 return -1;
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation first gets a list iterator that points to the end
 * of the list (with {@code listIterator(size())}). Then, it iterates
 * backwards over the list until the specified element is found, or the
 * beginning of the list is reached.
 *
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 */
 public int lastIndexOf(Object o) {
 ListIterator<E> it = listIterator(size());
 if (o==null) {
 while (it.hasPrevious())
 if (it.previous()==null)
 return it.nextIndex();
 } else {
 while (it.hasPrevious())
 if (o.equals(it.previous()))
 return it.nextIndex();
 }
 return -1;
 }
 
 
 // Bulk Operations
 
 /**
 * Removes all of the elements from this list (optional operation).
 * The list will be empty after this call returns.
 *
 * This implementation calls {@code removeRange(0, size())}.
 *
 * Note that this implementation throws an
 * {@code UnsupportedOperationException} unless {@code remove(int
 * index)} or {@code removeRange(int fromIndex, int toIndex)} is
 * overridden.
 *
 * @throws UnsupportedOperationException if the {@code clear} operation
 * is not supported by this list
 */
 public void clear() {
 removeRange(0, size());
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation gets an iterator over the specified collection
 * and iterates over it, inserting the elements obtained from the
 * iterator into this list at the appropriate position, one at a time,
 * using {@code add(int, E)}.
 * Many implementations will override this method for efficiency.
 *
 * Note that this implementation throws an
 * {@code UnsupportedOperationException} unless
 * {@link #add(int, Object) add(int, E)} is overridden.
 *
 * @throws UnsupportedOperationException {@inheritDoc}
 * @throws ClassCastException {@inheritDoc}
 * @throws NullPointerException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
 public boolean addAll(int index, Collection<? extends E> c) {
 rangeCheckForAdd(index);
 boolean modified = false;
 for (E e : c) {
 add(index++, e);
 modified = true;
 }
 return modified;
 }
 
 
 // Iterators
 
 /**
 * Returns an iterator over the elements in this list in proper sequence.
 *
 * This implementation returns a straightforward implementation of the
 * iterator interface, relying on the backing list's {@code size()},
 * {@code get(int)}, and {@code remove(int)} methods.
 *
 * Note that the iterator returned by this method will throw an
 * {@link UnsupportedOperationException} in response to its
 * {@code remove} method unless the list's {@code remove(int)} method is
 * overridden.
 *
 * This implementation can be made to throw runtime exceptions in the
 * face of concurrent modification, as described in the specification
 * for the (protected) {@link #modCount} field.
 *
 * @return an iterator over the elements in this list in proper sequence
 */
 public Iterator<E> iterator() {
 return new Itr();
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation returns {@code listIterator(0)}.
 *
 * @see #listIterator(int)
 */
 public ListIterator<E> listIterator() {
 return listIterator(0);
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation returns a straightforward implementation of the
 * {@code ListIterator} interface that extends the implementation of the
 * {@code Iterator} interface returned by the {@code iterator()} method.
 * The {@code ListIterator} implementation relies on the backing list's
 * {@code get(int)}, {@code set(int, E)}, {@code add(int, E)}
 * and {@code remove(int)} methods.
 *
 * Note that the list iterator returned by this implementation will
 * throw an {@link UnsupportedOperationException} in response to its
 * {@code remove}, {@code set} and {@code add} methods unless the
 * list's {@code remove(int)}, {@code set(int, E)}, and
 * {@code add(int, E)} methods are overridden.
 *
 * This implementation can be made to throw runtime exceptions in the
 * face of concurrent modification, as described in the specification for
 * the (protected) {@link #modCount} field.
 *
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
 public ListIterator<E> listIterator(final int index) {
 rangeCheckForAdd(index);
 
 return new ListItr(index);
 }
 
 private class Itr implements Iterator<E> {
 /**
 * Index of element to be returned by subsequent call to next.
 */
 int cursor = 0;
 
 /**
 * Index of element returned by most recent call to next or
 * previous. Reset to -1 if this element is deleted by a call
 * to remove.
 */
 int lastRet = -1;
 
 /**
 * The modCount value that the iterator believes that the backing
 * List should have. If this expectation is violated, the iterator
 * has detected concurrent modification.
 */
 int expectedModCount = modCount;
 
 public boolean hasNext() {
 return cursor != size();
 }
 
 public E next() {
 checkForComodification();
 try {
 int i = cursor;
 E next = get(i);
 lastRet = i;
 cursor = i + 1;
 return next;
 } catch (IndexOutOfBoundsException e) {
 checkForComodification();
 throw new NoSuchElementException();
 }
 }
 
 public void remove() {
 if (lastRet < 0)
 throw new IllegalStateException();
 checkForComodification();
 
 try {
 AbstractList.this.remove(lastRet);
 if (lastRet < cursor)
 cursor--;
 lastRet = -1;
 expectedModCount = modCount;
 } catch (IndexOutOfBoundsException e) {
 throw new ConcurrentModificationException();
 }
 }
 
 final void checkForComodification() {
 if (modCount != expectedModCount)
 throw new ConcurrentModificationException();
 }
 }
 
 private class ListItr extends Itr implements ListIterator<E> {
 ListItr(int index) {
 cursor = index;
 }
 
 public boolean hasPrevious() {
 return cursor != 0;
 }
 
 public E previous() {
 checkForComodification();
 try {
 int i = cursor - 1;
 E previous = get(i);
 lastRet = cursor = i;
 return previous;
 } catch (IndexOutOfBoundsException e) {
 checkForComodification();
 throw new NoSuchElementException();
 }
 }
 
 public int nextIndex() {
 return cursor;
 }
 
 public int previousIndex() {
 return cursor-1;
 }
 
 public void set(E e) {
 if (lastRet < 0)
 throw new IllegalStateException();
 checkForComodification();
 
 try {
 AbstractList.this.set(lastRet, e);
 expectedModCount = modCount;
 } catch (IndexOutOfBoundsException ex) {
 throw new ConcurrentModificationException();
 }
 }
 
 public void add(E e) {
 checkForComodification();
 
 try {
 int i = cursor;
 AbstractList.this.add(i, e);
 lastRet = -1;
 cursor = i + 1;
 expectedModCount = modCount;
 } catch (IndexOutOfBoundsException ex) {
 throw new ConcurrentModificationException();
 }
 }
 }
 
 /**
 * {@inheritDoc}
 *
 * This implementation returns a list that subclasses
 * {@code AbstractList}. The subclass stores, in private fields, the
 * offset of the subList within the backing list, the size of the subList
 * (which can change over its lifetime), and the expected
 * {@code modCount} value of the backing list. There are two variants
 * of the subclass, one of which implements {@code RandomAccess}.
 * If this list implements {@code RandomAccess} the returned list will
 * be an instance of the subclass that implements {@code RandomAccess}.
 *
 * The subclass's {@code set(int, E)}, {@code get(int)},
 * {@code add(int, E)}, {@code remove(int)}, {@code addAll(int,
 * Collection)} and {@code removeRange(int, int)} methods all
 * delegate to the corresponding methods on the backing abstract list,
 * after bounds-checking the index and adjusting for the offset. The
 * {@code addAll(Collection c)} method merely returns {@code addAll(size,
 * c)}.
 *
 * The {@code listIterator(int)} method returns a "wrapper object"
 * over a list iterator on the backing list, which is created with the
 * corresponding method on the backing list. The {@code iterator} method
 * merely returns {@code listIterator()}, and the {@code size} method
 * merely returns the subclass's {@code size} field.
 *
 * All methods first check to see if the actual {@code modCount} of
 * the backing list is equal to its expected value, and throw a
 * {@code ConcurrentModificationException} if it is not.
 *
 * @throws IndexOutOfBoundsException if an endpoint index value is out of range
 * {@code (fromIndex < 0 || toIndex > size)}
 * @throws IllegalArgumentException if the endpoint indices are out of order
 * {@code (fromIndex > toIndex)}
 */
 public List<E> subList(int fromIndex, int toIndex) {
 return (this instanceof RandomAccess ?
 new RandomAccessSubList<>(this, fromIndex, toIndex) :
 new SubList<>(this, fromIndex, toIndex));
 }
 
 // Comparison and hashing
 
 /**
 * Compares the specified object with this list for equality. Returns
 * {@code true} if and only if the specified object is also a list, both
 * lists have the same size, and all corresponding pairs of elements in
 * the two lists are equal. (Two elements {@code e1} and
 * {@code e2} are equal if {@code (e1==null ? e2==null :
 * e1.equals(e2))}.) In other words, two lists are defined to be
 * equal if they contain the same elements in the same order.
 *
 * This implementation first checks if the specified object is this
 * list. If so, it returns {@code true}; if not, it checks if the
 * specified object is a list. If not, it returns {@code false}; if so,
 * it iterates over both lists, comparing corresponding pairs of elements.
 * If any comparison returns {@code false}, this method returns
 * {@code false}. If either iterator runs out of elements before the
 * other it returns {@code false} (as the lists are of unequal length);
 * otherwise it returns {@code true} when the iterations complete.
 *
 * @param o the object to be compared for equality with this list
 * @return {@code true} if the specified object is equal to this list
 */
 public boolean equals(Object o) {
 if (o == this)
 return true;
 if (!(o instanceof List))
 return false;
 
 ListIterator<E> e1 = listIterator();
 ListIterator<?> e2 = ((List<?>) o).listIterator();
 while (e1.hasNext() && e2.hasNext()) {
 E o1 = e1.next();
 Object o2 = e2.next();
 if (!(o1==null ? o2==null : o1.equals(o2)))
 return false;
 }
 return !(e1.hasNext() || e2.hasNext());
 }
 
 /**
 * Returns the hash code value for this list.
 *
 * This implementation uses exactly the code that is used to define the
 * list hash function in the documentation for the {@link List#hashCode}
 * method.
 *
 * @return the hash code value for this list
 */
 public int hashCode() {
 int hashCode = 1;
 for (E e : this)
 hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
 return hashCode;
 }
 
 /**
 * Removes from this list all of the elements whose index is between
 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
 * Shifts any succeeding elements to the left (reduces their index).
 * This call shortens the list by {@code (toIndex - fromIndex)} elements.
 * (If {@code toIndex==fromIndex}, this operation has no effect.)
 *
 * This method is called by the {@code clear} operation on this list
 * and its subLists. Overriding this method to take advantage of
 * the internals of the list implementation can substantially
 * improve the performance of the {@code clear} operation on this list
 * and its subLists.
 *
 * This implementation gets a list iterator positioned before
 * {@code fromIndex}, and repeatedly calls {@code ListIterator.next}
 * followed by {@code ListIterator.remove} until the entire range has
 * been removed. Note: if {@code ListIterator.remove} requires linear
 * time, this implementation requires quadratic time.
 *
 * @param fromIndex index of first element to be removed
 * @param toIndex index after last element to be removed
 */
 protected void removeRange(int fromIndex, int toIndex) {
 ListIterator<E> it = listIterator(fromIndex);
 for (int i=0, n=toIndex-fromIndex; i<n; i++) {
 it.next();
 it.remove();
 }
 }
 
 /**
 * The number of times this list has been structurally modified.
 * Structural modifications are those that change the size of the
 * list, or otherwise perturb it in such a fashion that iterations in
 * progress may yield incorrect results.
 *
 * This field is used by the iterator and list iterator implementation
 * returned by the {@code iterator} and {@code listIterator} methods.
 * If the value of this field changes unexpectedly, the iterator (or list
 * iterator) will throw a {@code ConcurrentModificationException} in
 * response to the {@code next}, {@code remove}, {@code previous},
 * {@code set} or {@code add} operations. This provides
 * fail-fast behavior, rather than non-deterministic behavior in
 * the face of concurrent modification during iteration.
 *
 * Use of this field by subclasses is optional. If a subclass
 * wishes to provide fail-fast iterators (and list iterators), then it
 * merely has to increment this field in its {@code add(int, E)} and
 * {@code remove(int)} methods (and any other methods that it overrides
 * that result in structural modifications to the list). A single call to
 * {@code add(int, E)} or {@code remove(int)} must add no more than
 * one to this field, or the iterators (and list iterators) will throw
 * bogus {@code ConcurrentModificationExceptions}. If an implementation
 * does not wish to provide fail-fast iterators, this field may be
 * ignored.
 */
 protected transient int modCount = 0;
 
 private void rangeCheckForAdd(int index) {
 if (index < 0 || index > size())
 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
 }
 
 private String outOfBoundsMsg(int index) {
 return "Index: "+index+", Size: "+size();
 }
 }
 
 class SubList<E> extends AbstractList<E> {
 private final AbstractList<E> l;
 private final int offset;
 private int size;
 
 SubList(AbstractList<E> list, int fromIndex, int toIndex) {
 if (fromIndex < 0)
 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
 if (toIndex > list.size())
 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
 if (fromIndex > toIndex)
 throw new IllegalArgumentException("fromIndex(" + fromIndex +
 ") > toIndex(" + toIndex + ")");
 l = list;
 offset = fromIndex;
 size = toIndex - fromIndex;
 this.modCount = l.modCount;
 }
 
 public E set(int index, E element) {
 rangeCheck(index);
 checkForComodification();
 return l.set(index+offset, element);
 }
 
 public E get(int index) {
 rangeCheck(index);
 checkForComodification();
 return l.get(index+offset);
 }
 
 public int size() {
 checkForComodification();
 return size;
 }
 
 public void add(int index, E element) {
 rangeCheckForAdd(index);
 checkForComodification();
 l.add(index+offset, element);
 this.modCount = l.modCount;
 size++;
 }
 
 public E remove(int index) {
 rangeCheck(index);
 checkForComodification();
 E result = l.remove(index+offset);
 this.modCount = l.modCount;
 size--;
 return result;
 }
 
 protected void removeRange(int fromIndex, int toIndex) {
 checkForComodification();
 l.removeRange(fromIndex+offset, toIndex+offset);
 this.modCount = l.modCount;
 size -= (toIndex-fromIndex);
 }
 
 public boolean addAll(Collection<? extends E> c) {
 return addAll(size, c);
 }
 
 public boolean addAll(int index, Collection<? extends E> c) {
 rangeCheckForAdd(index);
 int cSize = c.size();
 if (cSize==0)
 return false;
 
 checkForComodification();
 l.addAll(offset+index, c);
 this.modCount = l.modCount;
 size += cSize;
 return true;
 }
 
 public Iterator<E> iterator() {
 return listIterator();
 }
 
 public ListIterator<E> listIterator(final int index) {
 checkForComodification();
 rangeCheckForAdd(index);
 
 return new ListIterator<E>() {
 private final ListIterator<E> i = l.listIterator(index+offset);
 
 public boolean hasNext() {
 return nextIndex() < size;
 }
 
 public E next() {
 if (hasNext())
 return i.next();
 else
 throw new NoSuchElementException();
 }
 
 public boolean hasPrevious() {
 return previousIndex() >= 0;
 }
 
 public E previous() {
 if (hasPrevious())
 return i.previous();
 else
 throw new NoSuchElementException();
 }
 
 public int nextIndex() {
 return i.nextIndex() - offset;
 }
 
 public int previousIndex() {
 return i.previousIndex() - offset;
 }
 
 public void remove() {
 i.remove();
 SubList.this.modCount = l.modCount;
 size--;
 }
 
 public void set(E e) {
 i.set(e);
 }
 
 public void add(E e) {
 i.add(e);
 SubList.this.modCount = l.modCount;
 size++;
 }
 };
 }
 
 public List<E> subList(int fromIndex, int toIndex) {
 return new SubList<>(this, fromIndex, toIndex);
 }
 
 private void rangeCheck(int index) {
 if (index < 0 || index >= size)
 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
 }
 
 private void rangeCheckForAdd(int index) {
 if (index < 0 || index > size)
 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
 }
 
 private String outOfBoundsMsg(int index) {
 return "Index: "+index+", Size: "+size;
 }
 
 private void checkForComodification() {
 if (this.modCount != l.modCount)
 throw new ConcurrentModificationException();
 }
 }
 
 class RandomAccessSubList<E> extends SubList<E> implements RandomAccess {
 RandomAccessSubList(AbstractList<E> list, int fromIndex, int toIndex) {
 super(list, fromIndex, toIndex);
 }
 
 public List<E> subList(int fromIndex, int toIndex) {
 return new RandomAccessSubList<>(this, fromIndex, toIndex);
 }
 }

然后看一下Iterable接口提供的

public interface Iterable<T> {
 /**
 * Returns an iterator over elements of type {@code T}.
 *
 * @return an Iterator.
 */
 Iterator<T> iterator();
 
 /**
 * Performs the given action for each element of the {@code Iterable}
 * until all elements have been processed or the action throws an
 * exception. Unless otherwise specified by the implementing class,
 * actions are performed in the order of iteration (if an iteration order
 * is specified). Exceptions thrown by the action are relayed to the
 * caller.
 *
 * @implSpec
 * The default implementation behaves as if:
 * <pre>{@code
 * for (T t : this)
 * action.accept(t);
 * }</pre>
 *
 * @param action The action to be performed for each element
 * @throws NullPointerException if the specified action is null
 * @since 1.8
 */
 default void forEach(Consumer<? super T> action) {
 Objects.requireNonNull(action);
 for (T t : this) {
 action.accept(t);
 }
 }
 
 /**
 * Creates a {@link Spliterator} over the elements described by this
 * {@code Iterable}.
 *
 * @implSpec
 * The default implementation creates an
 * <a href="Spliterator.html#binding">early-binding</a>
 * spliterator from the iterable's {@code Iterator}. The spliterator
 * inherits the fail-fast properties of the iterable's iterator.
 *
 * @implNote
 * The default implementation should usually be overridden. The
 * spliterator returned by the default implementation has poor splitting
 * capabilities, is unsized, and does not report any spliterator
 * characteristics. Implementing classes can nearly always provide a
 * better implementation.
 *
 * @return a {@code Spliterator} over the elements described by this
 * {@code Iterable}.
 * @since 1.8
 */
 default Spliterator<T> spliterator() {
 return Spliterators.spliteratorUnknownSize(iterator(), 0);
 }
 }

再来看一看set的接口情况

public interface Set<E> extends Collection<E> {
 // Query Operations
 
 /**
 * Returns the number of elements in this set (its cardinality). If this
 * set contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
 * <tt>Integer.MAX_VALUE</tt>.
 *
 * @return the number of elements in this set (its cardinality)
 */
 int size();
 
 /**
 * Returns <tt>true</tt> if this set contains no elements.
 *
 * @return <tt>true</tt> if this set contains no elements
 */
 boolean isEmpty();
 
 /**
 * Returns <tt>true</tt> if this set contains the specified element.
 * More formally, returns <tt>true</tt> if and only if this set
 * contains an element <tt>e</tt> such that
 * <tt>(o==null ? e==null : o.equals(e))</tt>.
 *
 * @param o element whose presence in this set is to be tested
 * @return <tt>true</tt> if this set contains the specified element
 * @throws ClassCastException if the type of the specified element
 * is incompatible with this set
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified element is null and this
 * set does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 */
 boolean contains(Object o);
 
 /**
 * Returns an iterator over the elements in this set. The elements are
 * returned in no particular order (unless this set is an instance of some
 * class that provides a guarantee).
 *
 * @return an iterator over the elements in this set
 */
 Iterator<E> iterator();
 
 /**
 * Returns an array containing all of the elements in this set.
 * If this set makes any guarantees as to what order its elements
 * are returned by its iterator, this method must return the
 * elements in the same order.
 *
 * The returned array will be "safe" in that no references to it
 * are maintained by this set. (In other words, this method must
 * allocate a new array even if this set is backed by an array).
 * The caller is thus free to modify the returned array.
 *
 * This method acts as bridge between array-based and collection-based
 * APIs.
 *
 * @return an array containing all the elements in this set
 */
 Object[] toArray();
 
 /**
 * Returns an array containing all of the elements in this set; the
 * runtime type of the returned array is that of the specified array.
 * If the set fits in the specified array, it is returned therein.
 * Otherwise, a new array is allocated with the runtime type of the
 * specified array and the size of this set.
 *
 * If this set fits in the specified array with room to spare
 * (i.e., the array has more elements than this set), the element in
 * the array immediately following the end of the set is set to
 * <tt>null</tt>. (This is useful in determining the length of this
 * set only if the caller knows that this set does not contain
 * any null elements.)
 *
 * If this set makes any guarantees as to what order its elements
 * are returned by its iterator, this method must return the elements
 * in the same order.
 *
 * Like the {@link #toArray()} method, this method acts as bridge between
 * array-based and collection-based APIs. Further, this method allows
 * precise control over the runtime type of the output array, and may,
 * under certain circumstances, be used to save allocation costs.
 *
 * Suppose <tt>x</tt> is a set known to contain only strings.
 * The following code can be used to dump the set into a newly allocated
 * array of <tt>String</tt>:
 *
 * <pre>
 * String[] y = x.toArray(new String[0]);</pre>
 *
 * Note that <tt>toArray(new Object[0])</tt> is identical in function to
 * <tt>toArray()</tt>.
 *
 * @param a the array into which the elements of this set are to be
 * stored, if it is big enough; otherwise, a new array of the same
 * runtime type is allocated for this purpose.
 * @return an array containing all the elements in this set
 * @throws ArrayStoreException if the runtime type of the specified array
 * is not a supertype of the runtime type of every element in this
 * set
 * @throws NullPointerException if the specified array is null
 */
 <T> T[] toArray(T[] a);
 
 
 // Modification Operations
 
 /**
 * Adds the specified element to this set if it is not already present
 * (optional operation). More formally, adds the specified element
 * <tt>e</tt> to this set if the set contains no element <tt>e2</tt>
 * such that
 * <tt>(e==null ? e2==null : e.equals(e2))</tt>.
 * If this set already contains the element, the call leaves the set
 * unchanged and returns <tt>false</tt>. In combination with the
 * restriction on constructors, this ensures that sets never contain
 * duplicate elements.
 *
 * The stipulation above does not imply that sets must accept all
 * elements; sets may refuse to add any particular element, including
 * <tt>null</tt>, and throw an exception, as described in the
 * specification for {@link Collection#add Collection.add}.
 * Individual set implementations should clearly document any
 * restrictions on the elements that they may contain.
 *
 * @param e element to be added to this set
 * @return <tt>true</tt> if this set did not already contain the specified
 * element
 * @throws UnsupportedOperationException if the <tt>add</tt> operation
 * is not supported by this set
 * @throws ClassCastException if the class of the specified element
 * prevents it from being added to this set
 * @throws NullPointerException if the specified element is null and this
 * set does not permit null elements
 * @throws IllegalArgumentException if some property of the specified element
 * prevents it from being added to this set
 */
 boolean add(E e);
 
 
 /**
 * Removes the specified element from this set if it is present
 * (optional operation). More formally, removes an element <tt>e</tt>
 * such that
 * <tt>(o==null ? e==null : o.equals(e))</tt>, if
 * this set contains such an element. Returns <tt>true</tt> if this set
 * contained the element (or equivalently, if this set changed as a
 * result of the call). (This set will not contain the element once the
 * call returns.)
 *
 * @param o object to be removed from this set, if present
 * @return <tt>true</tt> if this set contained the specified element
 * @throws ClassCastException if the type of the specified element
 * is incompatible with this set
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified element is null and this
 * set does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
 * is not supported by this set
 */
 boolean remove(Object o);
 
 
 // Bulk Operations
 
 /**
 * Returns <tt>true</tt> if this set contains all of the elements of the
 * specified collection. If the specified collection is also a set, this
 * method returns <tt>true</tt> if it is a subset of this set.
 *
 * @param c collection to be checked for containment in this set
 * @return <tt>true</tt> if this set contains all of the elements of the
 * specified collection
 * @throws ClassCastException if the types of one or more elements
 * in the specified collection are incompatible with this
 * set
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if the specified collection contains one
 * or more null elements and this set does not permit null
 * elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #contains(Object)
 */
 boolean containsAll(Collection<?> c);
 
 /**
 * Adds all of the elements in the specified collection to this set if
 * they're not already present (optional operation). If the specified
 * collection is also a set, the <tt>addAll</tt> operation effectively
 * modifies this set so that its value is the union of the two
 * sets. The behavior of this operation is undefined if the specified
 * collection is modified while the operation is in progress.
 *
 * @param c collection containing elements to be added to this set
 * @return <tt>true</tt> if this set changed as a result of the call
 *
 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
 * is not supported by this set
 * @throws ClassCastException if the class of an element of the
 * specified collection prevents it from being added to this set
 * @throws NullPointerException if the specified collection contains one
 * or more null elements and this set does not permit null
 * elements, or if the specified collection is null
 * @throws IllegalArgumentException if some property of an element of the
 * specified collection prevents it from being added to this set
 * @see #add(Object)
 */
 boolean addAll(Collection<? extends E> c);
 
 /**
 * Retains only the elements in this set that are contained in the
 * specified collection (optional operation). In other words, removes
 * from this set all of its elements that are not contained in the
 * specified collection. If the specified collection is also a set, this
 * operation effectively modifies this set so that its value is the
 * intersection of the two sets.
 *
 * @param c collection containing elements to be retained in this set
 * @return <tt>true</tt> if this set changed as a result of the call
 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
 * is not supported by this set
 * @throws ClassCastException if the class of an element of this set
 * is incompatible with the specified collection
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this set contains a null element and the
 * specified collection does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 */
 boolean retainAll(Collection<?> c);
 
 /**
 * Removes from this set all of its elements that are contained in the
 * specified collection (optional operation). If the specified
 * collection is also a set, this operation effectively modifies this
 * set so that its value is the asymmetric set difference of
 * the two sets.
 *
 * @param c collection containing elements to be removed from this set
 * @return <tt>true</tt> if this set changed as a result of the call
 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
 * is not supported by this set
 * @throws ClassCastException if the class of an element of this set
 * is incompatible with the specified collection
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this set contains a null element and the
 * specified collection does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 * @see #contains(Object)
 */
 boolean removeAll(Collection<?> c);
 
 /**
 * Removes all of the elements from this set (optional operation).
 * The set will be empty after this call returns.
 *
 * @throws UnsupportedOperationException if the <tt>clear</tt> method
 * is not supported by this set
 */
 void clear();
 
 
 // Comparison and hashing
 
 /**
 * Compares the specified object with this set for equality. Returns
 * <tt>true</tt> if the specified object is also a set, the two sets
 * have the same size, and every member of the specified set is
 * contained in this set (or equivalently, every member of this set is
 * contained in the specified set). This definition ensures that the
 * equals method works properly across different implementations of the
 * set interface.
 *
 * @param o object to be compared for equality with this set
 * @return <tt>true</tt> if the specified object is equal to this set
 */
 boolean equals(Object o);
 
 /**
 * Returns the hash code value for this set. The hash code of a set is
 * defined to be the sum of the hash codes of the elements in the set,
 * where the hash code of a <tt>null</tt> element is defined to be zero.
 * This ensures that <tt>s1.equals(s2)</tt> implies that
 * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt>
 * and <tt>s2</tt>, as required by the general contract of
 * {@link Object#hashCode}.
 *
 * @return the hash code value for this set
 * @see Object#equals(Object)
 * @see Set#equals(Object)
 */
 int hashCode();
 
 /**
 * Creates a {@code Spliterator} over the elements in this set.
 *
 * The {@code Spliterator} reports {@link Spliterator#DISTINCT}.
 * Implementations should document the reporting of additional
 * characteristic values.
 *
 * @implSpec
 * The default implementation creates a
 * <a href="Spliterator.html#binding">late-binding</a> spliterator
 * from the set's {@code Iterator}. The spliterator inherits the
 * fail-fast properties of the set's iterator.
 * 
 * The created {@code Spliterator} additionally reports
 * {@link Spliterator#SIZED}.
 *
 * @implNote
 * The created {@code Spliterator} additionally reports
 * {@link Spliterator#SUBSIZED}.
 *
 * @return a {@code Spliterator} over the elements in this set
 * @since 1.8
 */
 @Override
 default Spliterator<E> spliterator() {
 return Spliterators.spliterator(this, Spliterator.DISTINCT);
 }
 }

看看AbstractSet

public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> {
 /**
 * Sole constructor. (For invocation by subclass constructors, typically
 * implicit.)
 */
 protected AbstractSet() {
 }
 
 // Comparison and hashing
 
 /**
 * Compares the specified object with this set for equality. Returns
 * <tt>true</tt> if the given object is also a set, the two sets have
 * the same size, and every member of the given set is contained in
 * this set. This ensures that the <tt>equals</tt> method works
 * properly across different implementations of the <tt>Set</tt>
 * interface.
 *
 * This implementation first checks if the specified object is this
 * set; if so it returns <tt>true</tt>. Then, it checks if the
 * specified object is a set whose size is identical to the size of
 * this set; if not, it returns false. If so, it returns
 * <tt>containsAll((Collection) o)</tt>.
 *
 * @param o object to be compared for equality with this set
 * @return <tt>true</tt> if the specified object is equal to this set
 */
 public boolean equals(Object o) {
 if (o == this)
 return true;
 
 if (!(o instanceof Set))
 return false;
 Collection<?> c = (Collection<?>) o;
 if (c.size() != size())
 return false;
 try {
 return containsAll(c);
 } catch (ClassCastException unused) {
 return false;
 } catch (NullPointerException unused) {
 return false;
 }
 }
 
 /**
 * Returns the hash code value for this set. The hash code of a set is
 * defined to be the sum of the hash codes of the elements in the set,
 * where the hash code of a <tt>null</tt> element is defined to be zero.
 * This ensures that <tt>s1.equals(s2)</tt> implies that
 * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt>
 * and <tt>s2</tt>, as required by the general contract of
 * {@link Object#hashCode}.
 *
 * This implementation iterates over the set, calling the
 * <tt>hashCode</tt> method on each element in the set, and adding up
 * the results.
 *
 * @return the hash code value for this set
 * @see Object#equals(Object)
 * @see Set#equals(Object)
 */
 public int hashCode() {
 int h = 0;
 Iterator<E> i = iterator();
 while (i.hasNext()) {
 E obj = i.next();
 if (obj != null)
 h += obj.hashCode();
 }
 return h;
 }
 
 /**
 * Removes from this set all of its elements that are contained in the
 * specified collection (optional operation). If the specified
 * collection is also a set, this operation effectively modifies this
 * set so that its value is the asymmetric set difference of
 * the two sets.
 *
 * This implementation determines which is the smaller of this set
 * and the specified collection, by invoking the <tt>size</tt>
 * method on each. If this set has fewer elements, then the
 * implementation iterates over this set, checking each element
 * returned by the iterator in turn to see if it is contained in
 * the specified collection. If it is so contained, it is removed
 * from this set with the iterator's <tt>remove</tt> method. If
 * the specified collection has fewer elements, then the
 * implementation iterates over the specified collection, removing
 * from this set each element returned by the iterator, using this
 * set's <tt>remove</tt> method.
 *
 * Note that this implementation will throw an
 * <tt>UnsupportedOperationException</tt> if the iterator returned by the
 * <tt>iterator</tt> method does not implement the <tt>remove</tt> method.
 *
 * @param c collection containing elements to be removed from this set
 * @return <tt>true</tt> if this set changed as a result of the call
 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
 * is not supported by this set
 * @throws ClassCastException if the class of an element of this set
 * is incompatible with the specified collection
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this set contains a null element and the
 * specified collection does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 * @see #contains(Object)
 */
 public boolean removeAll(Collection<?> c) {
 Objects.requireNonNull(c);
 boolean modified = false;
 
 if (size() > c.size()) {
 for (Iterator<?> i = c.iterator(); i.hasNext(); )
 modified |= remove(i.next());
 } else {
 for (Iterator<?> i = iterator(); i.hasNext(); ) {
 if (c.contains(i.next())) {
 i.remove();
 modified = true;
 }
 }
 }
 return modified;
 }
 
 }

综上就是一些我们在一些具体的实现类中要用到的接口和抽象的类，我们在用的时候最好深入看看每个方法是怎么实现的，以便我们在用时更好的使用，一遍看不懂再看一遍。

[70]: /images/20220512/8032e116af624bab9281e3f96d68005c.png