Iterable和Iterator

Iterator中定义的方法
default void forEachRemaining​(Consumer<? super E> action)	Performs the given action for each remaining element until all elements have been processed or the action throws an exception.
boolean hasNext()	Returns true if the iteration has more elements.
E next()	Returns the next element in the iteration.
default void remove()	Removes from the underlying collection the last element returned by this iterator (optional operat

3.调用next()方法时，迭代器九月过下一个元素，并返回刚刚越过的那个元素的引用。
4.remove()方法将会删除上次调用next方法返回的元素。调用remove()方法之前必须调用next()方法，二者之间有依赖性。

Iterable接口中定义的方法
default void forEach​(Consumer<? super T> action)	Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception
Iterator iterator()	Returns an iterator over elements of type T
default Spliterator spliterator()	Creates a Spliterator over the elements described by this Iterable

1.iterator方法用于返回一个实现了Iterator接口的对象。可以用这个迭代器对象依次访问集合中的每一个元素。
2.Collection接口扩展了Iterable接口，因此，对于标准类库中的任何集合都可以使用for each循环，也可以通过调用iterator.forEachRemaining方法并提供一个lambda表达式。iterator.forEachRemaining(element -> do somethig with element)
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