ArrayList 中的 forEachRemaining方法是做什么的？

Question

我正在研究 ArrayList 实现并找到了 forEachRemaining 方法。这个或者什么时候调用这个方法有什么用？public class ArrayList<E> extends AbstractList<E>        implements List<E>, RandomAccess, Cloneable, java.io.Serializable{    //...    //...    private class Itr implements Iterator<E> {        //...        @Override        @SuppressWarnings("unchecked")        public void forEachRemaining(Consumer<? super E> consumer) {            Objects.requireNonNull(consumer);            final int size = ArrayList.this.size;            int i = cursor;            if (i >= size) {                return;            }            final Object[] elementData = ArrayList.this.elementData;            if (i >= elementData.length) {                throw new ConcurrentModificationException();            }            while (i != size && modCount == expectedModCount) {                consumer.accept((E) elementData[i++]);            }            // update once at end of iteration to reduce heap write traffic            cursor = i;            lastRet = i - 1;            checkForComodification();        }    }}

Answer 1

ArrayList没有forEachRemaining，迭代器等它返回做。

从文档中Iterator：

对每个剩余元素执行给定的操作，直到处理完所有元素或操作引发异常。如果指定了该顺序，则操作按迭代顺序执行。动作抛出的异常被转发给调用者。

Answer 2

如果使用迭代器遍历列表，next()则它将返回该列表中的下一个元素。因此，假设您没有遍历完整列表并调用forEachRemaining()它，那么它将列表中未遍历的剩余元素。

演示

List<String> list = new ArrayList<>();

list.add("one");

list.add("two");

list.add("three");

list.add("four");

list.add("five");

//added five element in list

Iterator<String> iterator =  list.iterator();

//visiting two elements by called next()

System.out.println("Printed by next():" + iterator.next());

System.out.println("Printed by next():" + iterator.next());

//remaining un-visited elements can be accessed using forEachRemaining()

iterator.forEachRemaining(s -> {System.out.println( "Printed by forEachRemaining():" + s);});

输出：

Printed by next():one

Printed by next():two

Printed by forEachRemaining():three

Printed by forEachRemaining():four

Printed by forEachRemaining():five