Collections.EMPTY_LIST 和 Collections.emptyList()的区别

本文主要是介绍Collections.EMPTY_LIST 和 Collections.emptyList()的区别，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

Collections中的EMPTY_LIST 和 emptyList 其实通过源码查看，他们最终都是同一个final的不变的实例对象

public static final List EMPTY_LIST = new EmptyList<>();

public static final <T> List<T> emptyList() {

    return (List<T>) EMPTY_LIST;
}

在Collections中自定义了一个内部类EmptyList，该内部类继承了AbstractList的抽象类，拥有了list的数据结构

并重写了get方法

private static class EmptyList<E>  extends AbstractList<E>

    implements RandomAccess, Serializable {private static final long serialVersionUID = 8842843931221139166L;public Iterator<E> iterator() {return emptyIterator();}public ListIterator<E> listIterator() {return emptyListIterator();}public int size() {return 0;}public boolean isEmpty() {return true;}public boolean contains(Object obj) {return false;}public boolean containsAll(Collection<?> c) { return c.isEmpty(); }public Object[] toArray() { return new Object[0]; }public <T> T[] toArray(T[] a) {if (a.length > 0)a[0] = null;return a;}

    //重写该get方法，禁止该方法去获取对象，使用时抛出下标越界public E get(int index) {throw new IndexOutOfBoundsException("Index: "+index);}public boolean equals(Object o) {return (o instanceof List) && ((List<?>)o).isEmpty();}public int hashCode() { return 1; }@Override
    public boolean removeIf(Predicate<? super E> filter) {Objects.requireNonNull(filter);return false;}@Override
    public void replaceAll(UnaryOperator<E> operator) {Objects.requireNonNull(operator);}@Override
    public void sort(Comparator<? super E> c) {}// Override default methods in Collection
    @Override
    public void forEach(Consumer<? super E> action) {Objects.requireNonNull(action);}@Override
    public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); }// Preserves singleton property
    private Object readResolve() {return EMPTY_LIST;}
}