如何修复LinkedHashSet的大小？ [英] How to fix size of LinkedHashSet?

问题描述

我需要一个固定大小为n的LinkedHashSet，这样当我们插入第n + 1个元素时，第一个元素会自动删除，并在结尾处插入新元素。

I need a LinkedHashSet with a fixed size n so that when we insert the n+1th element , the first element is automatically removed and new element is inserted at the end.

LinkedHashSet <Integer> = new LinkedHashSet <Integer> () ;

我应该如何实现构造函数来修复大小？

How should I implement the constructor to fix the size ?

推荐答案

默认情况下，LinkedHashSet对此无能为力。您可以在此阅读有关原因： https://stackoverflow.com/a/7632240/9337345

By default LinkedHashSet is not capable for this. You can read about the reasons here: https://stackoverflow.com/a/7632240/9337345

您可以做的唯一事情就是创建一个继承的LinkedHashSet，它可以根据您的需要负责固定大小。

The only thing what you can do is to create an inherited LinkedHashSet which is responsible for the fixed size as you desire.

例如：

For example:

import java.util.Iterator;
import java.util.LinkedHashSet;

public class MyLinkedHashSet<T> extends LinkedHashSet<T> {
    private long maxSize;

    public MyLinkedHashSet(long maxSize) {
        this.maxSize = maxSize;
    }

    @Override
    public boolean add(T item) {
        if(size() == maxSize) {
            removeFirst();
        }
        return super.add(item);
    }

    private void removeFirst() {
        if(size() > 0) {
            Iterator<T> iterator = iterator();
            T item = iterator.next();
            remove(item);
        }
    }

    public static void main(String[] args) {
        LinkedHashSet<Integer> set = new MyLinkedHashSet<>(3);
        set.add(1);
        set.add(2);
        set.add(3);
        set.add(4);
        System.out.println(set);    // [2, 3, 4]
        set.clear();
        System.out.println(set);    // []
        set.addAll(Arrays.asList(1, 2, 3, 4, 5));
        System.out.println(set);    // [3, 4, 5]
    }
}

我希望这就是你的意思。

I hope this is what you meant.

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