为什么迭代器方法同时存在于Iterable和Collection接口中？ [英] Why is the iterator method present in both Iterable and Collection interfaces?

问题描述

Iterable 接口具有以下方法：

 Iterator<T> iterator();

Collection 界面扩展了 Iterable ，并且还声明了相同的方法。

The Collection interface extends Iterable, and it also declares the same method.

我怀疑在设计Java集合时需要两次将相同的方法声明放入两次吗？

I am doubtful what was the need of putting the same method declaration twice while designing Java collections?

推荐答案

主要原因是Java 5。

The main reason is Java 5.

java.util.Collection 与自Java 1.2起就存在它的 iterator（）方法和 java.util.Iterator 。

java.util.Collection with its iterator() method and java.util.Iterator exist since Java 1.2.

当他们想在Java 5中引入增强的for循环（一个 for（String s：...）{} 时，他们需要一个从未实现 java.util.Collection 的类中创建 java.util.Iterator 的方法。引入了一个新接口 java.lang.Iterable ，该接口可以由所有想要支持增强的for循环的类实现。

When they wanted to introduce the enhanced for loop in Java 5 (the one for (String s: ...) {}, they needed a way to create a java.util.Iterator from classes that do not implement java.util.Collection. The decision was made to introduce a new interface java.lang.Iterable that can be implemented by all classes that want to support the enhanced for loop.

为了使现有的 java.util.Collection 及其所有后代接口和类与增强的for循环兼容，他们制作了 java .util.Collection 扩展 java.lang .Iterable 。

To make the existing java.util.Collection and all it's descendent interfaces and classes compatible with the enhanced for loop, they made java.util.Collection extend java.lang.Iterable.

因此，两个接口都有一个方法 iterator（）- java.util.Collection ，因为它是第一个诞生的， java.lang.Iterable 用于支持增强的for循环。

Therefore both interfaces have a method iterator() - java.util.Collection because it was the "first born", java.lang.Iterable for supporting the enhanced for loop.

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