Arrays.asList()

将数组转换成List集合

    /*** Returns a fixed-size list backed by the specified array.  (Changes to* the returned list "write through" to the array.)  This method acts* as bridge between array-based and collection-based APIs, in* combination with {@link Collection#toArray}.  The returned list is* serializable and implements {@link RandomAccess}.** <p>This method also provides a convenient way to create a fixed-size* list initialized to contain several elements:* <pre>*     List&lt;String&gt; stooges = Arrays.asList("Larry", "Moe", "Curly");* </pre>** @param <T> the class of the objects in the array* @param a the array by which the list will be backed* @return a list view of the specified array*/@SafeVarargs@SuppressWarnings("varargs")public static <T> List<T> asList(T... a) {return new ArrayList<>(a);}

Arrays.ArrayList

    /*** @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);}@Overridepublic int size() {return a.length;}@Overridepublic 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;}@Overridepublic E get(int index) {return a[index];}@Overridepublic E set(int index, E element) {E oldValue = a[index];a[index] = element;return oldValue;}@Overridepublic 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;}@Overridepublic boolean contains(Object o) {return indexOf(o) != -1;}@Overridepublic Spliterator<E> spliterator() {return Spliterators.spliterator(a, Spliterator.ORDERED);}@Overridepublic void forEach(Consumer<? super E> action) {Objects.requireNonNull(action);for (E e : a) {action.accept(e);}}@Overridepublic 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]);}}@Overridepublic void sort(Comparator<? super E> c) {Arrays.sort(a, c);}}

UnsupportedOperationException

Arrays.asList创建list，当向这个List添加或删除元素时，会报java.lang.UnsupportedOperationException

从源码中可知，Arrays.asList创建的ArrayList是Arrays的一个静态内部类，其中add、remove、clear方法都是没有实现的。

那么子类没有实现这些方法，肯定是调用了父类的方法

AbstractList.java

 AbstractList.java/*** {@inheritDoc}** <p>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();}