java collection集合框架使用,出现:java.lang.UnsupportedOperationException

Bertha 。 2022-05-28 01:43 79阅读 0赞

我个人的情况是在使用Arrays.asList(strings)将数组转为list的时候,

在asList.remove(i)时候出现的异常,后来看源码,发现**Arrays的asList方法返回的是一个固定大小的list**,

然后在Arrays类,发现了一个**内部的ArryasList类**,里面并没有对集合大小进行操作的方法,

因此用Arrays类的asList方法转换的list,试图做改变大小的操作会报java.lang.UnsupportedOperationException异常,

而**asList方法返回的就是这个Arrays类私有的ArrayList对象**

public static String removeStartingNumStr (String str,int num){
    		String[] strings = getStrings(str);
    		List<String> asList = Arrays.asList(strings);
    		String numStr = String.valueOf(num);
    		for (int i = 0; i < asList.size(); i++) {
    			if(asList.get(i).equals(numStr)){
    				asList.remove(i);
    				--i;
    			}else{
    				break;
    			}
    		}
    		String[] array = (String[])asList.toArray();
    		String endStr = getLongStrToStrArr(array);
    		return endStr;
    	}

内部的ArrayList类如下图:

@SafeVarargs
        @SuppressWarnings("varargs")
        public static <T> List<T> asList(T... a) {
            return new ArrayList<>(a);
        }
    
        /**
         * @serial include
         */
        private static class ArrayList<E> extends AbstractList<E>
            implements RandomAccess, java.io.Serializable
        {
            private static final long serialVersionUID = -2764017481108945198L;
            private final E[] a;
    
            ArrayList(E[] array) {
                a = Objects.requireNonNull(array);
            }
    
            @Override
            public int size() {
                return a.length;
            }
    
            @Override
            public Object[] toArray() {
                return a.clone();
            }
    
            @Override
            @SuppressWarnings("unchecked")
            public <T> T[] toArray(T[] a) {
                int size = size();
                if (a.length < size)
                    return Arrays.copyOf(this.a, size,
                                         (Class<? extends T[]>) a.getClass());
                System.arraycopy(this.a, 0, a, 0, size);
                if (a.length > size)
                    a[size] = null;
                return a;
            }
    
            @Override
            public E get(int index) {
                return a[index];
            }
    
            @Override
            public E set(int index, E element) {
                E oldValue = a[index];
                a[index] = element;
                return oldValue;
            }
    
            @Override
            public int indexOf(Object o) {
                E[] a = this.a;
                if (o == null) {
                    for (int i = 0; i < a.length; i++)
                        if (a[i] == null)
                            return i;
                } else {
                    for (int i = 0; i < a.length; i++)
                        if (o.equals(a[i]))
                            return i;
                }
                return -1;
            }
    
            @Override
            public boolean contains(Object o) {
                return indexOf(o) != -1;
            }
    
            @Override
            public Spliterator<E> spliterator() {
                return Spliterators.spliterator(a, Spliterator.ORDERED);
            }
    
            @Override
            public void forEach(Consumer<? super E> action) {
                Objects.requireNonNull(action);
                for (E e : a) {
                    action.accept(e);
                }
            }
    
            @Override
            public void replaceAll(UnaryOperator<E> operator) {
                Objects.requireNonNull(operator);
                E[] a = this.a;
                for (int i = 0; i < a.length; i++) {
                    a[i] = operator.apply(a[i]);
                }
            }
    
            @Override
            public void sort(Comparator<? super E> c) {
                Arrays.sort(a, c);
            }
        }
    
     }

在asList方法中,鼠标移到返回的

public static <T> List<T> asList(T... a) {
            return new ArrayList<>(a);

上显示是这个包

#####  #####

java. util. Arrays. ArrayList.ArrayList< T>(  T\[\] array)

说明返回的是Arrays类的内部的ArrayList对象,不同于其他的ArrayList对象