JAVA容器Set的三种子类的比较

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Set 概述

1.包含三个具体子类：HashSet、LinkedHashSet、TreeSet（还有一个  AbstractSet的抽象类）2.Set及其子类的实例不能含有重复元素

三个子类的区别

1. HashSet:打印结果与插入顺序无关

import java.util.*public class TestHashSet{    public static void main(String[] args){        //Creat HashSet        Set<String> set = new HashSet<String>();        //Add elements to HashSet        set.add("London");        set.add("Paris");        set.add("New York");        set.add("San Francisco");        set.add("Beijing");        set.add("New York");        System.out.println(set);    }}

Output：

[San Francisco, New York, Paris, Beijing, London]

2. LinkedHashSet:打印结果与插入顺序一致

import java.util.*public class TestHashSet{    public static void main(String[] args){        //Creat HashSet (polymorphism)        Set<String> set = new LinkedHashSet<String>();        //Add elements to HashSet        set.add("London");        set.add("Paris");        set.add("New York");        set.add("San Francisco");        set.add("Beijing");        set.add("New York");        System.out.println(set);    }}

Output：

[London, Paris, New York, San Francisco, Beijing]

3. TreeSet:按升序/降序排列

import java.util.*public class TestHashSet{    public static void main(String[] args){        //Creat HashSet        Set<String> set = new HashSet<String>();        //Add elements to HashSet        set.add("London");        set.add("Paris");        set.add("New York");        set.add("San Francisco");        set.add("Beijing");        set.add("New York");        //construct an instant and sort one time         TreeSet<String> treeSet = new TreeSet<String>(set);        System.out.println(treeSet);    }}

output:

[Beijing, London, New York, Paris, San Francisco]

Reference: 《Introduction to Java Programming》

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