Question

我正在研究ArrayList的实现，并发现了forEachRemaining方法。或当我们调用此方法时有什么用途？

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，迭代器等返回了。

来自the documentation for Iterator：

对每个剩余元素执行给定的操作，直到所有元素都已处理或该操作引发异常。如果指定了顺序，则按照迭代顺序执行操作。该操作引发的异常会中继到调用方。

Answer 2

如果使用next()在列表上遍历，则使用Iterator，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了forEachRemaining()，那么它将保留列表中未遍历的元素。

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

ArrayList中的forEachRemaining（Consumer <！-？super E-> Consumer）方法有什么作用？

2 个答案: