ArrayList.java中List接口的冗余实现 [英] Redundant implementation of List interface in ArrayList.java

问题描述

可能重复：

为什么ArrayList有implements List？

我是新的java我试图看到集合接口的层次结构。我发现 AbstractList.java 的签名类似于

I am new to java I was trying to see the hierarchy of collection interface. I found that the signature of AbstractList.java is like

public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E>

它实现List接口。但是如果你看看子类ArrayList.java的签名，它看起来像

It implements List interface. But if you look at signature of child class ArrayList.java it looks like

public class ArrayList<E> extends AbstractList<E>   implements List<E>, RandomAccess, Cloneable, java.io.Serializable

已经实现的List接口，那么为什么子类再次实现相同的接口（ List ）。

If you look parent class is already implemented List interface then why child class is again implementing same interface (List).

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推荐答案

这

Is there specific reason or requirement behind this

我不这么认为。删除第二个 List< E> 对编译器来说绝对不会改变。

I don't think so. Removing the second List<E> would change absolutely nothing as far as the compiler is concerned.

我的两个假设是：

1. 这是因为历史原因。
   
c $ c> 是-a List< E> （这可能是关于 ArrayList 的唯一最重要的事情）。

1. It's there for historic reasons. However, I can't find any evidence to support this.
2. It's included for documentation purposes, to make it immediately clear than an ArrayList<E> is-a List<E> (this is probably the single most important thing to know about ArrayList).

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