java set集合

set集合的学习

set集合可以去重，不能重复添加

package com.tedu.study01;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class Study_Set {
    public static void main(String[] args) {
        Set<String> s1 = new HashSet<>();
        s1.add("赵玉梅");
        s1.add("张飞");
        s1.add("关羽");
        s1.add("关心");
        System.out.println(s1.size());
        System.out.println(s1.isEmpty());
        System.out.println(s1.contains("关羽"));
        Iterator<String> iterator = s1.iterator();
        for (String s : s1) {
            System.out.println(s);
        }
    }
}

新创建的对象必须重写hashcode和equals方法才能够去重

package com.tedu.study01;

import java.util.HashSet;
import java.util.List;
import java.util.Objects;
import java.util.Set;

public class Demo {
    public static void main(String[] args) {
        Set<Student> li = new HashSet<>();
        Student s1 = new Student("赵云",19,"北京");
        Student s2 = new Student("关羽",33,"南京");
        Student s3 = new Student("赵云",19,"北京");
        Student s4 = new Student("关羽",33,"南京");
        li.add(s1);
        li.add(s2);
        li.add(s3);
        li.add(s4);
        System.out.println(li);
    }
}
class Student{
    private String name;
    private int age;
    private String addr;
    public Student(){

    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return age == student.age &&
                Objects.equals(name, student.name) &&
                Objects.equals(addr, student.addr);
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", addr='" + addr + '\'' +
                '}';
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age, addr);
    }

    public Student(String name, int age, String addr) {
        this.name = name;
        this.age = age;
        this.addr = addr;
    }

    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;
    }

    public String getAddr() {
        return addr;
    }

    public void setAddr(String addr) {
        this.addr = addr;
    }
}