特点:

　　无序,不重复

HashSet和TreeSet

 

HashSet

HashSet扩展AbstractSet并且实现Set接口,底层使用HashSet

HashSet的内部操作的底层数据是HashMap,只是我们操作的是HashMap的key

区分可以采用重写equals()和hashCode()方法

package com.Set;import java.util.HashSet;public class HahSetDemo {  public static void main(String[] args) {    HashSet
     
       data=new HashSet
      
       ();    //不允许重复,实际操作的是hashmap里面的键  键只允许唯一    data.add("张三");    data.add("李四");    data.add("王五");    System.out.println(data.add("张三"));    System.out.println(data);    //没有重复   对象都是new出来的    HashSet
       
         data2=new HashSet
        
         ();    data2.add(new Student1("张三", 20));    data2.add(new Student1("李四", 30));    System.out.println(data2.add(new Student1("张三", 20)));}}class Student1{    private String name;    private int age;    public Student1(String name, int age) {                this.name = name;        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    @Override    public int hashCode() {        final int prime = 31;        int result = 1;        result = prime * result + age;        result = prime * result + ((name == null) ? 0 : name.hashCode());        return result;    }    @Override    public boolean equals(Object obj) {        if (this == obj)            return true;        if (obj == null)            return false;        if (getClass() != obj.getClass())            return false;        Student1 other = (Student1) obj;        if (age != other.age)            return false;        if (name == null) {            if (other.name != null)                return false;        } else if (!name.equals(other.name))            return false;        return true;    };        }