Java Arrays.asList()需要注意的坑(返回对象不支持add()和remove()方法)

我不是女神ヾ 2023-01-13 09:50 105阅读 0赞

由于Arrays.asList()返回的类型是java.util.Arrays.ArrayList，而不是java.util.ArrayList，所以不支持add()和remove()方法。

以下是java.util.Arrays.ArrayList的源码：

/**
         * @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);
            }
        }

如果需要使用java.util.ArrayList的add()和remove()方法，需要使用new ArrayList(Arrays.asList())将返回类型变为java.util.ArrayList。

List<String> strList=new ArrayList(Arrays.asList(new String[]{"1","2"}));