为什么LinkedList 和arraylist 在java 中扩展了AbstractList? [英] Why LinkedList and arraylist extends AbstractList in java?

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<覆盖/code>，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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