Java集合-Vector

男娘i 2022-05-30 05:17 192阅读 0赞

Vector底层是一个可增长的Object数组集合，可根据整型index下标去获取Vector集合元素，Vector的大小会在集合添加元素或删除元素后自动改变；

Vector会有一个容量和容量增量，其容量不小于集合的真实大小，当Vector数组溢出时会增加容量；

Vector的实现是线程同步的【synchronized】；在用迭代器遍历Vector集合对象时，如果遍历过程中对集合对象的内容进行了修改（增加、删除、修改），则会抛出ConcurrentModificationException，即迭代器的快速失败（fail—fast）机制。

Vector每次添加元素都会校验底层数组长度，数组长度不够时则扩容，扩容后，数组扩大为原来的2倍。

![20180305204203287][]

Vector集合的基本结构

Vector源码如下：

public class Vector<E>
 extends AbstractList<E>
 implements List<E>, RandomAccess, Cloneable, java.io.Serializable
 {
 /**
 * The array buffer into which the components of the vector are
 * stored. The capacity of the vector is the length of this array buffer,
 * and is at least large enough to contain all the vector's elements.
 */
 protected Object[] elementData;
 
 /**
 * The number of valid components in this {@code Vector} object.
 */
 protected int elementCount;
 
 /**
 * The amount by which the capacity of the vector is automatically
 * incremented when its size becomes greater than its capacity. If
 * the capacity increment is less than or equal to zero, the capacity
 * of the vector is doubled each time it needs to grow.
 */
 protected int capacityIncrement;
 
 /** use serialVersionUID from JDK 1.0.2 for interoperability */
 private static final long serialVersionUID = -2767605614048989439L;
 
 /**
 * Constructs an empty vector with the specified initial capacity and
 * capacity increment.
 */
 public Vector(int initialCapacity, int capacityIncrement) {
 super();
 if (initialCapacity < 0)
 throw new IllegalArgumentException("Illegal Capacity: "+
 initialCapacity);
 this.elementData = new Object[initialCapacity];
 this.capacityIncrement = capacityIncrement;
 }
 
 /**
 * Constructs an empty vector with the specified initial capacity and
 * with its capacity increment equal to zero.
 */
 public Vector(int initialCapacity) {
 this(initialCapacity, 0);
 }
 
 /**
 * Constructs an empty vector so that its internal data array
 * has size {@code 10} and its standard capacity increment is
 * zero.
 */
 public Vector() {
 this(10);
 }
 
 /**
 * Constructs a vector containing the elements of the specified
 * collection, in the order they are returned by the collection's
 * iterator.
 *
 * @param c the collection whose elements are to be placed into this
 * vector
 * @throws NullPointerException if the specified collection is null
 * @since 1.2
 */
 public Vector(Collection<? extends E> c) {
 elementData = c.toArray();
 elementCount = elementData.length;
 // c.toArray might (incorrectly) not return Object[] (see 6260652)
 if (elementData.getClass() != Object[].class)
 elementData = Arrays.copyOf(elementData, elementCount, Object[].class);
 }
 
 /**
 * Copies the components of this vector into the specified array.
 * The item at index {@code k} in this vector is copied into
 * component {@code k} of {@code anArray}.
 */
 public synchronized void copyInto(Object[] anArray) {
 System.arraycopy(elementData, 0, anArray, 0, elementCount);
 }
 
 /**
 * Trims the capacity of this vector to be the vector's current
 * size. If the capacity of this vector is larger than its current
 * size, then the capacity is changed to equal the size by replacing
 * its internal data array, kept in the field {@code elementData},
 * with a smaller one. An application can use this operation to
 * minimize the storage of a vector.
 */
 public synchronized void trimToSize() {
 modCount++;
 int oldCapacity = elementData.length;
 if (elementCount < oldCapacity) {
 elementData = Arrays.copyOf(elementData, elementCount);
 }
 }
 
 /**
 * Increases the capacity of this vector, if necessary, to ensure
 * that it can hold at least the number of components specified by
 * the minimum capacity argument.
 *
 * If the current capacity of this vector is less than
 * {@code minCapacity}, then its capacity is increased by replacing its
 * internal data array, kept in the field {@code elementData}, with a
 * larger one. The size of the new data array will be the old size plus
 * {@code capacityIncrement}, unless the value of
 * {@code capacityIncrement} is less than or equal to zero, in which case
 * the new capacity will be twice the old capacity; but if this new size
 * is still smaller than {@code minCapacity}, then the new capacity will
 * be {@code minCapacity}.
 *
 * @param minCapacity the desired minimum capacity
 */
 public synchronized void ensureCapacity(int minCapacity) {
 if (minCapacity > 0) {
 modCount++;
 ensureCapacityHelper(minCapacity);
 }
 }
 
 /**
 * This implements the unsynchronized semantics of ensureCapacity.
 * Synchronized methods in this class can internally call this
 * method for ensuring capacity without incurring the cost of an
 * extra synchronization.
 *
 * @see #ensureCapacity(int)
 */
 private void ensureCapacityHelper(int minCapacity) {
 // overflow-conscious code
 if (minCapacity - elementData.length > 0)
 grow(minCapacity);
 }
 
 /**
 * The maximum size of array to allocate.
 * 数组分配的最大长度
 */
 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
 
 private void grow(int minCapacity) {
 // overflow-conscious code
 int oldCapacity = elementData.length;
 int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
 capacityIncrement : oldCapacity);
 if (newCapacity - minCapacity < 0)
 newCapacity = minCapacity;
 if (newCapacity - MAX_ARRAY_SIZE > 0)
 newCapacity = hugeCapacity(minCapacity);
 elementData = Arrays.copyOf(elementData, newCapacity);
 }
 
 private static int hugeCapacity(int minCapacity) {
 if (minCapacity < 0) // overflow
 throw new OutOfMemoryError();
 return (minCapacity > MAX_ARRAY_SIZE) ?
 Integer.MAX_VALUE :
 MAX_ARRAY_SIZE;
 }
 
 /**
 * Sets the size of this vector. If the new size is greater than the
 * current size, new {@code null} items are added to the end of
 * the vector. If the new size is less than the current size, all
 * components at index {@code newSize} and greater are discarded.
 */
 public synchronized void setSize(int newSize) {
 modCount++;
 if (newSize > elementCount) {
 ensureCapacityHelper(newSize);
 } else {
 for (int i = newSize ; i < elementCount ; i++) {
 elementData[i] = null;
 }
 }
 elementCount = newSize;
 }
 
 /**
 * Returns the current capacity of this vector.
 */
 public synchronized int capacity() {
 return elementData.length;
 }
 
 /**
 * Returns the number of components in this vector.
 */
 public synchronized int size() {
 return elementCount;
 }
 
 /**
 * Tests if this vector has no components.
 */
 public synchronized boolean isEmpty() {
 return elementCount == 0;
 }
 
 /**
 * Returns an enumeration of the components of this vector. The
 * returned {@code Enumeration} object will generate all items in
 * this vector. The first item generated is the item at index {@code 0},
 * then the item at index {@code 1}, and so on.
 *
 * @return an enumeration of the components of this vector
 * @see Iterator
 */
 public Enumeration<E> elements() {
 return new Enumeration<E>() {
 int count = 0;
 
 public boolean hasMoreElements() {
 return count < elementCount;
 }
 
 public E nextElement() {
 synchronized (Vector.this) {
 if (count < elementCount) {
 return elementData(count++);
 }
 }
 throw new NoSuchElementException("Vector Enumeration");
 }
 };
 }
 
 /**
 * Returns {@code true} if this vector contains the specified element.
 * More formally, returns {@code true} if and only if this vector
 * contains at least one element {@code e} such that
 * <tt>(o==null ? e==null : o.equals(e))</tt>.
 *
 * @param o element whose presence in this vector is to be tested
 * @return {@code true} if this vector contains the specified element
 */
 public boolean contains(Object o) {
 return indexOf(o, 0) >= 0;
 }
 
 /**
 * Returns the index of the first occurrence of the specified element
 * in this vector, or -1 if this vector does not contain the element.
 * More formally, returns the lowest index {@code i} 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 vector, or -1 if this vector does not contain the element
 */
 public int indexOf(Object o) {
 return indexOf(o, 0);
 }
 
 /**
 * Returns the index of the first occurrence of the specified element in
 * this vector, searching forwards from {@code index}, or returns -1 if
 * the element is not found.
 * More formally, returns the lowest index {@code i} such that
 * <tt>(i >= index && (o==null ? get(i)==null : o.equals(get(i))))</tt>,
 * or -1 if there is no such index.
 *
 * @param o element to search for
 * @param index index to start searching from
 * @return the index of the first occurrence of the element in
 * this vector at position {@code index} or later in the vector;
 * {@code -1} if the element is not found.
 * @throws IndexOutOfBoundsException if the specified index is negative
 * @see Object#equals(Object)
 */
 public synchronized int indexOf(Object o, int index) {
 if (o == null) {
 for (int i = index ; i < elementCount ; i++)
 if (elementData[i]==null)
 return i;
 } else {
 for (int i = index ; i < elementCount ; i++)
 if (o.equals(elementData[i]))
 return i;
 }
 return -1;
 }
 
 /**
 * Returns the index of the last occurrence of the specified element
 * in this vector, or -1 if this vector does not contain the element.
 * More formally, returns the highest index {@code i} 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 vector, or -1 if this vector does not contain the element
 */
 public synchronized int lastIndexOf(Object o) {
 return lastIndexOf(o, elementCount-1);
 }
 
 /**
 * Returns the index of the last occurrence of the specified element in
 * this vector, searching backwards from {@code index}, or returns -1 if
 * the element is not found.
 * More formally, returns the highest index {@code i} such that
 * <tt>(i <= index && (o==null ? get(i)==null : o.equals(get(i))))</tt>,
 * or -1 if there is no such index.
 *
 * @param o element to search for
 * @param index index to start searching backwards from
 * @return the index of the last occurrence of the element at position
 * less than or equal to {@code index} in this vector;
 * -1 if the element is not found.
 * @throws IndexOutOfBoundsException if the specified index is greater
 * than or equal to the current size of this vector
 */
 public synchronized int lastIndexOf(Object o, int index) {
 if (index >= elementCount)
 throw new IndexOutOfBoundsException(index + " >= "+ elementCount);
 
 if (o == null) {
 for (int i = index; i >= 0; i--)
 if (elementData[i]==null)
 return i;
 } else {
 for (int i = index; i >= 0; i--)
 if (o.equals(elementData[i]))
 return i;
 }
 return -1;
 }
 
 /**
 * Returns the component at the specified index.
 *
 * This method is identical in functionality to the {@link #get(int)}
 * method (which is part of the {@link List} interface).
 *
 * @param index an index into this vector
 * @return the component at the specified index
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index >= size()})
 */
 public synchronized E elementAt(int index) {
 if (index >= elementCount) {
 throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
 }
 
 return elementData(index);
 }
 
 /**
 * Returns the first component (the item at index {@code 0}) of
 * this vector.
 *
 * @return the first component of this vector
 * @throws NoSuchElementException if this vector has no components
 */
 public synchronized E firstElement() {
 if (elementCount == 0) {
 throw new NoSuchElementException();
 }
 return elementData(0);
 }
 
 /**
 * Returns the last component of the vector.
 *
 * @return the last component of the vector, i.e., the component at index
 * <code>size() - 1</code>.
 * @throws NoSuchElementException if this vector is empty
 */
 public synchronized E lastElement() {
 if (elementCount == 0) {
 throw new NoSuchElementException();
 }
 return elementData(elementCount - 1);
 }
 
 /**
 * Sets the component at the specified {@code index} of this
 * vector to be the specified object. The previous component at that
 * position is discarded.
 *
 * The index must be a value greater than or equal to {@code 0}
 * and less than the current size of the vector.
 *
 * This method is identical in functionality to the
 * {@link #set(int, Object) set(int, E)}
 * method (which is part of the {@link List} interface). Note that the
 * {@code set} method reverses the order of the parameters, to more closely
 * match array usage. Note also that the {@code set} method returns the
 * old value that was stored at the specified position.
 *
 * @param obj what the component is to be set to
 * @param index the specified index
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index >= size()})
 */
 public synchronized void setElementAt(E obj, int index) {
 if (index >= elementCount) {
 throw new ArrayIndexOutOfBoundsException(index + " >= " +
 elementCount);
 }
 elementData[index] = obj;
 }
 
 /**
 * Deletes the component at the specified index. Each component in
 * this vector with an index greater or equal to the specified
 * {@code index} is shifted downward to have an index one
 * smaller than the value it had previously. The size of this vector
 * is decreased by {@code 1}.
 *
 * The index must be a value greater than or equal to {@code 0}
 * and less than the current size of the vector.
 *
 * This method is identical in functionality to the {@link #remove(int)}
 * method (which is part of the {@link List} interface). Note that the
 * {@code remove} method returns the old value that was stored at the
 * specified position.
 *
 * @param index the index of the object to remove
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index >= size()})
 */
 public synchronized void removeElementAt(int index) {
 modCount++;
 if (index >= elementCount) {
 throw new ArrayIndexOutOfBoundsException(index + " >= " +
 elementCount);
 }
 else if (index < 0) {
 throw new ArrayIndexOutOfBoundsException(index);
 }
 int j = elementCount - index - 1;
 if (j > 0) {
 System.arraycopy(elementData, index + 1, elementData, index, j);
 }
 elementCount--;
 elementData[elementCount] = null; /* to let gc do its work */
 }
 
 /**
 * Inserts the specified object as a component in this vector at the
 * specified {@code index}. Each component in this vector with
 * an index greater or equal to the specified {@code index} is
 * shifted upward to have an index one greater than the value it had
 * previously.
 *
 * The index must be a value greater than or equal to {@code 0}
 * and less than or equal to the current size of the vector. (If the
 * index is equal to the current size of the vector, the new element
 * is appended to the Vector.)
 *
 * This method is identical in functionality to the
 * {@link #add(int, Object) add(int, E)}
 * method (which is part of the {@link List} interface). Note that the
 * {@code add} method reverses the order of the parameters, to more closely
 * match array usage.
 *
 * @param obj the component to insert
 * @param index where to insert the new component
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index > size()})
 */
 public synchronized void insertElementAt(E obj, int index) {
 modCount++;
 if (index > elementCount) {
 throw new ArrayIndexOutOfBoundsException(index
 + " > " + elementCount);
 }
 ensureCapacityHelper(elementCount + 1);
 System.arraycopy(elementData, index, elementData, index + 1, elementCount - index);
 elementData[index] = obj;
 elementCount++;
 }
 
 /**
 * Adds the specified component to the end of this vector,
 * increasing its size by one. The capacity of this vector is
 * increased if its size becomes greater than its capacity.
 *
 * This method is identical in functionality to the
 * {@link #add(Object) add(E)}
 * method (which is part of the {@link List} interface).
 *
 * @param obj the component to be added
 */
 public synchronized void addElement(E obj) {
 modCount++;
 ensureCapacityHelper(elementCount + 1);
 elementData[elementCount++] = obj;
 }
 
 /**
 * Removes the first (lowest-indexed) occurrence of the argument
 * from this vector. If the object is found in this vector, each
 * component in the vector with an index greater or equal to the
 * object's index is shifted downward to have an index one smaller
 * than the value it had previously.
 *
 * This method is identical in functionality to the
 * {@link #remove(Object)} method (which is part of the
 * {@link List} interface).
 *
 * @param obj the component to be removed
 * @return {@code true} if the argument was a component of this
 * vector; {@code false} otherwise.
 */
 public synchronized boolean removeElement(Object obj) {
 modCount++;
 int i = indexOf(obj);
 if (i >= 0) {
 removeElementAt(i);
 return true;
 }
 return false;
 }
 
 /**
 * Removes all components from this vector and sets its size to zero.
 *
 * This method is identical in functionality to the {@link #clear}
 * method (which is part of the {@link List} interface).
 */
 public synchronized void removeAllElements() {
 modCount++;
 // Let gc do its work
 for (int i = 0; i < elementCount; i++)
 elementData[i] = null;
 
 elementCount = 0;
 }
 
 /**
 * Returns a clone of this vector. The copy will contain a
 * reference to a clone of the internal data array, not a reference
 * to the original internal data array of this {@code Vector} object.
 *
 * @return a clone of this vector
 */
 public synchronized Object clone() {
 try {
 @SuppressWarnings("unchecked")
 Vector<E> v = (Vector<E>) super.clone();
 v.elementData = Arrays.copyOf(elementData, elementCount);
 v.modCount = 0;
 return v;
 } catch (CloneNotSupportedException e) {
 // this shouldn't happen, since we are Cloneable
 throw new InternalError(e);
 }
 }
 
 /**
 * Returns an array containing all of the elements in this Vector
 * in the correct order.
 *
 * @since 1.2
 */
 public synchronized Object[] toArray() {
 return Arrays.copyOf(elementData, elementCount);
 }
 
 /**
 * Returns an array containing all of the elements in this Vector in the
 * correct order; the runtime type of the returned array is that of the
 * specified array. If the Vector 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 Vector.
 *
 * If the Vector fits in the specified array with room to spare
 * (i.e., the array has more elements than the Vector),
 * the element in the array immediately following the end of the
 * Vector is set to null. (This is useful in determining the length
 * of the Vector only if the caller knows that the Vector
 * does not contain any null elements.)
 *
 * @param a the array into which the elements of the Vector 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 the Vector
 * @throws ArrayStoreException if the runtime type of a is not a supertype
 * of the runtime type of every element in this Vector
 * @throws NullPointerException if the given array is null
 * @since 1.2
 */
 @SuppressWarnings("unchecked")
 public synchronized <T> T[] toArray(T[] a) {
 if (a.length < elementCount)
 return (T[]) Arrays.copyOf(elementData, elementCount, a.getClass());
 
 System.arraycopy(elementData, 0, a, 0, elementCount);
 
 if (a.length > elementCount)
 a[elementCount] = null;
 
 return a;
 }
 
 // Positional Access Operations
 
 @SuppressWarnings("unchecked")
 E elementData(int index) {
 return (E) elementData[index];
 }
 
 /**
 * Returns the element at the specified position in this Vector.
 *
 * @param index index of the element to return
 * @return object at the specified index
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index >= size()})
 * @since 1.2
 */
 public synchronized E get(int index) {
 if (index >= elementCount)
 throw new ArrayIndexOutOfBoundsException(index);
 
 return elementData(index);
 }
 
 /**
 * Replaces the element at the specified position in this Vector with the
 * specified element.
 *
 * @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 ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index >= size()})
 * @since 1.2
 */
 public synchronized E set(int index, E element) {
 if (index >= elementCount)
 throw new ArrayIndexOutOfBoundsException(index);
 
 E oldValue = elementData(index);
 elementData[index] = element;
 return oldValue;
 }
 
 /**
 * Appends the specified element to the end of this Vector.
 *
 * @param e element to be appended to this Vector
 * @return {@code true} (as specified by {@link Collection#add})
 * @since 1.2
 */
 public synchronized boolean add(E e) {
 modCount++;
 ensureCapacityHelper(elementCount + 1);
 elementData[elementCount++] = e;
 return true;
 }
 
 /**
 * Removes the first occurrence of the specified element in this Vector
 * If the Vector does not contain the element, it is unchanged. More
 * formally, removes the element with the lowest index i such that
 * {@code (o==null ? get(i)==null : o.equals(get(i)))} (if such
 * an element exists).
 *
 * @param o element to be removed from this Vector, if present
 * @return true if the Vector contained the specified element
 * @since 1.2
 */
 public boolean remove(Object o) {
 return removeElement(o);
 }
 
 /**
 * Inserts the specified element at the specified position in this Vector.
 * 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 ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index > size()})
 * @since 1.2
 */
 public void add(int index, E element) {
 insertElementAt(element, index);
 }
 
 /**
 * Removes the element at the specified position in this Vector.
 * Shifts any subsequent elements to the left (subtracts one from their
 * indices). Returns the element that was removed from the Vector.
 *
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index >= size()})
 * @param index the index of the element to be removed
 * @return element that was removed
 * @since 1.2
 */
 public synchronized E remove(int index) {
 modCount++;
 if (index >= elementCount)
 throw new ArrayIndexOutOfBoundsException(index);
 E oldValue = elementData(index);
 
 int numMoved = elementCount - index - 1;
 if (numMoved > 0)
 System.arraycopy(elementData, index+1, elementData, index,
 numMoved);
 elementData[--elementCount] = null; // Let gc do its work
 
 return oldValue;
 }
 
 /**
 * Removes all of the elements from this Vector. The Vector will
 * be empty after this call returns (unless it throws an exception).
 *
 * @since 1.2
 */
 public void clear() {
 removeAllElements();
 }
 
 // Bulk Operations
 
 /**
 * Returns true if this Vector contains all of the elements in the
 * specified Collection.
 *
 * @param c a collection whose elements will be tested for containment
 * in this Vector
 * @return true if this Vector contains all of the elements in the
 * specified collection
 * @throws NullPointerException if the specified collection is null
 */
 public synchronized boolean containsAll(Collection<?> c) {
 return super.containsAll(c);
 }
 
 /**
 * Appends all of the elements in the specified Collection to the end of
 * this Vector, 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.
 * (This implies that the behavior of this call is undefined if the
 * specified Collection is this Vector, and this Vector is nonempty.)
 *
 * @param c elements to be inserted into this Vector
 * @return {@code true} if this Vector changed as a result of the call
 * @throws NullPointerException if the specified collection is null
 * @since 1.2
 */
 public synchronized boolean addAll(Collection<? extends E> c) {
 modCount++;
 Object[] a = c.toArray();
 int numNew = a.length;
 ensureCapacityHelper(elementCount + numNew);
 System.arraycopy(a, 0, elementData, elementCount, numNew);
 elementCount += numNew;
 return numNew != 0;
 }
 
 /**
 * Removes from this Vector all of its elements that are contained in the
 * specified Collection.
 *
 * @param c a collection of elements to be removed from the Vector
 * @return true if this Vector changed as a result of the call
 * @throws ClassCastException if the types of one or more elements
 * in this vector are incompatible with the specified
 * collection
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this vector contains one or more null
 * elements and the specified collection does not support null
 * elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @since 1.2
 */
 public synchronized boolean removeAll(Collection<?> c) {
 return super.removeAll(c);
 }
 
 /**
 * Retains only the elements in this Vector that are contained in the
 * specified Collection. In other words, removes from this Vector all
 * of its elements that are not contained in the specified Collection.
 *
 * @param c a collection of elements to be retained in this Vector
 * (all other elements are removed)
 * @return true if this Vector changed as a result of the call
 * @throws ClassCastException if the types of one or more elements
 * in this vector are incompatible with the specified
 * collection
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this vector contains one or more null
 * elements and the specified collection does not support null
 * elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @since 1.2
 */
 public synchronized boolean retainAll(Collection<?> c) {
 return super.retainAll(c);
 }
 
 /**
 * Inserts all of the elements in the specified Collection into this
 * Vector at the specified position. 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 the Vector
 * in the order that they are returned by the specified Collection's
 * iterator.
 *
 * @param index index at which to insert the first element from the
 * specified collection
 * @param c elements to be inserted into this Vector
 * @return {@code true} if this Vector changed as a result of the call
 * @throws ArrayIndexOutOfBoundsException if the index is out of range
 * ({@code index < 0 || index > size()})
 * @throws NullPointerException if the specified collection is null
 * @since 1.2
 */
 public synchronized boolean addAll(int index, Collection<? extends E> c) {
 modCount++;
 if (index < 0 || index > elementCount)
 throw new ArrayIndexOutOfBoundsException(index);
 
 Object[] a = c.toArray();
 int numNew = a.length;
 ensureCapacityHelper(elementCount + numNew);
 
 int numMoved = elementCount - index;
 if (numMoved > 0)
 System.arraycopy(elementData, index, elementData, index + numNew,
 numMoved);
 
 System.arraycopy(a, 0, elementData, index, numNew);
 elementCount += numNew;
 return numNew != 0;
 }
 
 /**
 * Compares the specified Object with this Vector for equality. Returns
 * 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.
 *
 * @param o the Object to be compared for equality with this Vector
 * @return true if the specified Object is equal to this Vector
 */
 public synchronized boolean equals(Object o) {
 return super.equals(o);
 }
 
 /**
 * Returns the hash code value for this Vector.
 */
 public synchronized int hashCode() {
 return super.hashCode();
 }
 
 /**
 * Returns a string representation of this Vector, containing
 * the String representation of each element.
 */
 public synchronized String toString() {
 return super.toString();
 }
 
 /**
 * Returns a view of the portion of this List between fromIndex,
 * inclusive, and toIndex, exclusive. (If fromIndex and toIndex are
 * equal, the returned List is empty.) The returned List is backed by this
 * List, so 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 operating on a subList view
 * instead of a whole List. For example, the following idiom
 * removes a range of elements from a List:
 * <pre>
 * list.subList(from, to).clear();
 * </pre>
 * Similar idioms may be constructed for indexOf and lastIndexOf,
 * and all of the algorithms in the Collections 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 the 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 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 synchronized List<E> subList(int fromIndex, int toIndex) {
 return Collections.synchronizedList(super.subList(fromIndex, toIndex),
 this);
 }
 
 /**
 * 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.)
 */
 protected synchronized void removeRange(int fromIndex, int toIndex) {
 modCount++;
 int numMoved = elementCount - toIndex;
 System.arraycopy(elementData, toIndex, elementData, fromIndex,
 numMoved);
 
 // Let gc do its work
 int newElementCount = elementCount - (toIndex-fromIndex);
 while (elementCount != newElementCount)
 elementData[--elementCount] = null;
 }
 
 /**
 * Save the state of the {@code Vector} instance to a stream (that
 * is, serialize it).
 * This method performs synchronization to ensure the consistency
 * of the serialized data.
 */
 private void writeObject(java.io.ObjectOutputStream s)
 throws java.io.IOException {
 final java.io.ObjectOutputStream.PutField fields = s.putFields();
 final Object[] data;
 synchronized (this) {
 fields.put("capacityIncrement", capacityIncrement);
 fields.put("elementCount", elementCount);
 data = elementData.clone();
 }
 fields.put("elementData", data);
 s.writeFields();
 }
 
 /**
 * 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.
 *
 * The returned list iterator is <a href="#fail-fast">fail-fast</a>.
 *
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
 public synchronized ListIterator<E> listIterator(int index) {
 if (index < 0 || index > elementCount)
 throw new IndexOutOfBoundsException("Index: "+index);
 return new ListItr(index);
 }
 
 /**
 * Returns a list iterator over the elements in this list (in proper
 * sequence).
 *
 * The returned list iterator is <a href="#fail-fast">fail-fast</a>.
 *
 * @see #listIterator(int)
 */
 public synchronized ListIterator<E> listIterator() {
 return new ListItr(0);
 }
 
 /**
 * Returns an iterator over the elements in this list in proper sequence.
 *
 * The returned iterator is <a href="#fail-fast">fail-fast</a>.
 *
 * @return an iterator over the elements in this list in proper sequence
 */
 public synchronized Iterator<E> iterator() {
 return new Itr();
 }
 
 /**
 * An optimized version of AbstractList.Itr
 */
 private class Itr implements Iterator<E> {
 int cursor; // index of next element to return
 int lastRet = -1; // index of last element returned; -1 if no such
 int expectedModCount = modCount;
 
 public boolean hasNext() {
 // Racy but within spec, since modifications are checked
 // within or after synchronization in next/previous
 return cursor != elementCount;
 }
 
 public E next() {
 synchronized (Vector.this) {
 checkForComodification();
 int i = cursor;
 if (i >= elementCount)
 throw new NoSuchElementException();
 cursor = i + 1;
 return elementData(lastRet = i);
 }
 }
 
 public void remove() {
 if (lastRet == -1)
 throw new IllegalStateException();
 synchronized (Vector.this) {
 checkForComodification();
 Vector.this.remove(lastRet);
 expectedModCount = modCount;
 }
 cursor = lastRet;
 lastRet = -1;
 }
 
 @Override
 public void forEachRemaining(Consumer<? super E> action) {
 Objects.requireNonNull(action);
 synchronized (Vector.this) {
 final int size = elementCount;
 int i = cursor;
 if (i >= size) {
 return;
 }
 @SuppressWarnings("unchecked")
 final E[] elementData = (E[]) Vector.this.elementData;
 if (i >= elementData.length) {
 throw new ConcurrentModificationException();
 }
 while (i != size && modCount == expectedModCount) {
 action.accept(elementData[i++]);
 }
 // update once at end of iteration to reduce heap write traffic
 cursor = i;
 lastRet = i - 1;
 checkForComodification();
 }
 }
 
 final void checkForComodification() {
 if (modCount != expectedModCount)
 throw new ConcurrentModificationException();
 }
 }
 
 /**
 * An optimized version of AbstractList.ListItr
 */
 final class ListItr extends Itr implements ListIterator<E> {
 ListItr(int index) {
 super();
 cursor = index;
 }
 
 public boolean hasPrevious() {
 return cursor != 0;
 }
 
 public int nextIndex() {
 return cursor;
 }
 
 public int previousIndex() {
 return cursor - 1;
 }
 
 public E previous() {
 synchronized (Vector.this) {
 checkForComodification();
 int i = cursor - 1;
 if (i < 0)
 throw new NoSuchElementException();
 cursor = i;
 return elementData(lastRet = i);
 }
 }
 
 public void set(E e) {
 if (lastRet == -1)
 throw new IllegalStateException();
 synchronized (Vector.this) {
 checkForComodification();
 Vector.this.set(lastRet, e);
 }
 }
 
 public void add(E e) {
 int i = cursor;
 synchronized (Vector.this) {
 checkForComodification();
 Vector.this.add(i, e);
 expectedModCount = modCount;
 }
 cursor = i + 1;
 lastRet = -1;
 }
 }
 
 @Override
 public synchronized void forEach(Consumer<? super E> action) {
 Objects.requireNonNull(action);
 final int expectedModCount = modCount;
 @SuppressWarnings("unchecked")
 final E[] elementData = (E[]) this.elementData;
 final int elementCount = this.elementCount;
 for (int i=0; modCount == expectedModCount && i < elementCount; i++) {
 action.accept(elementData[i]);
 }
 if (modCount != expectedModCount) {
 throw new ConcurrentModificationException();
 }
 }
 
 @Override
 @SuppressWarnings("unchecked")
 public synchronized boolean removeIf(Predicate<? super E> filter) {
 Objects.requireNonNull(filter);
 // figure out which elements are to be removed
 // any exception thrown from the filter predicate at this stage
 // will leave the collection unmodified
 int removeCount = 0;
 final int size = elementCount;
 final BitSet removeSet = new BitSet(size);
 final int expectedModCount = modCount;
 for (int i=0; modCount == expectedModCount && i < size; i++) {
 @SuppressWarnings("unchecked")
 final E element = (E) elementData[i];
 if (filter.test(element)) {
 removeSet.set(i);
 removeCount++;
 }
 }
 if (modCount != expectedModCount) {
 throw new ConcurrentModificationException();
 }
 
 // shift surviving elements left over the spaces left by removed elements
 final boolean anyToRemove = removeCount > 0;
 if (anyToRemove) {
 final int newSize = size - removeCount;
 for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
 i = removeSet.nextClearBit(i);
 elementData[j] = elementData[i];
 }
 for (int k=newSize; k < size; k++) {
 elementData[k] = null; // Let gc do its work
 }
 elementCount = newSize;
 if (modCount != expectedModCount) {
 throw new ConcurrentModificationException();
 }
 modCount++;
 }
 
 return anyToRemove;
 }
 
 @Override
 @SuppressWarnings("unchecked")
 public synchronized void replaceAll(UnaryOperator<E> operator) {
 Objects.requireNonNull(operator);
 final int expectedModCount = modCount;
 final int size = elementCount;
 for (int i=0; modCount == expectedModCount && i < size; i++) {
 elementData[i] = operator.apply((E) elementData[i]);
 }
 if (modCount != expectedModCount) {
 throw new ConcurrentModificationException();
 }
 modCount++;
 }
 
 @SuppressWarnings("unchecked")
 @Override
 public synchronized void sort(Comparator<? super E> c) {
 final int expectedModCount = modCount;
 Arrays.sort((E[]) elementData, 0, elementCount, c);
 if (modCount != expectedModCount) {
 throw new ConcurrentModificationException();
 }
 modCount++;
 }
 
 /**
 * Creates a <a href="Spliterator.html#binding">late-binding</a>
 * and fail-fast {@link Spliterator} over the elements in this
 * list.
 *
 * The {@code Spliterator} reports {@link Spliterator#SIZED},
 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
 * Overriding implementations should document the reporting of additional
 * characteristic values.
 *
 * @return a {@code Spliterator} over the elements in this list
 * @since 1.8
 */
 @Override
 public Spliterator<E> spliterator() {
 return new VectorSpliterator<>(this, null, 0, -1, 0);
 }
 
 /** Similar to ArrayList Spliterator */
 static final class VectorSpliterator<E> implements Spliterator<E> {
 private final Vector<E> list;
 private Object[] array;
 private int index; // current index, modified on advance/split
 private int fence; // -1 until used; then one past last index
 private int expectedModCount; // initialized when fence set
 
 /** Create new spliterator covering the given range */
 VectorSpliterator(Vector<E> list, Object[] array, int origin, int fence,
 int expectedModCount) {
 this.list = list;
 this.array = array;
 this.index = origin;
 this.fence = fence;
 this.expectedModCount = expectedModCount;
 }
 
 private int getFence() { // initialize on first use
 int hi;
 if ((hi = fence) < 0) {
 synchronized(list) {
 array = list.elementData;
 expectedModCount = list.modCount;
 hi = fence = list.elementCount;
 }
 }
 return hi;
 }
 
 public Spliterator<E> trySplit() {
 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
 return (lo >= mid) ? null :
 new VectorSpliterator<E>(list, array, lo, index = mid,
 expectedModCount);
 }
 
 @SuppressWarnings("unchecked")
 public boolean tryAdvance(Consumer<? super E> action) {
 int i;
 if (action == null)
 throw new NullPointerException();
 if (getFence() > (i = index)) {
 index = i + 1;
 action.accept((E)array[i]);
 if (list.modCount != expectedModCount)
 throw new ConcurrentModificationException();
 return true;
 }
 return false;
 }
 
 @SuppressWarnings("unchecked")
 public void forEachRemaining(Consumer<? super E> action) {
 int i, hi; // hoist accesses and checks from loop
 Vector<E> lst; Object[] a;
 if (action == null)
 throw new NullPointerException();
 if ((lst = list) != null) {
 if ((hi = fence) < 0) {
 synchronized(lst) {
 expectedModCount = lst.modCount;
 a = array = lst.elementData;
 hi = fence = lst.elementCount;
 }
 }
 else
 a = array;
 if (a != null && (i = index) >= 0 && (index = hi) <= a.length) {
 while (i < hi)
 action.accept((E) a[i++]);
 if (lst.modCount == expectedModCount)
 return;
 }
 }
 throw new ConcurrentModificationException();
 }
 
 public long estimateSize() {
 return (long) (getFence() - index);
 }
 
 public int characteristics() {
 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
 }
 }
 }

[20180305204203287]: /images/20220530/4b5bbac1b386474c8847ee667c1ea459.png