为什么LinkedList 和arraylist 在java 中扩展了AbstractList?

问题描述

为什么LinkedList 和ArrayList 在Java 中扩展了AbstractList?

Why LinkedList and ArrayList extends AbstractList in Java?

当我们想在实现类中指定一个共同的行为时使用抽象类.

Abstract classes are used when we want to specify a common behaviour in implementation classes.

但是 AbstractList 中的所有方法都被 ArrayList 和 LinkedList 覆盖.

But all the methods which are in AbstractList are overridden by ArrayList and LinkedList.

那么扩展这个类有什么用?

So what is the use of extending this class?

推荐答案

subList(int,int) 方法不会被 ArrayList 和 LinkedList，并为此AbstractList提供了一个通用的实现

subList(int,int) method is not overriden by both ArrayList and LinkedList, and for this AbstractList provides a common implementation

来自 Java 源代码

From Java source

public List<E> subList(int fromIndex, int toIndex) {
        return (this instanceof RandomAccess ?
                new RandomAccessSubList<E>(this, fromIndex, toIndex) :
                new SubList<E>(this, fromIndex, toIndex));
    }

此外还有其他没有被覆盖的方法，如 toString() 和 iterator()

In addition there are other methods which are not overriden like toString() and iterator()

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