set里的面试题

package set;

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

/**
 * @auto dh
 * @create 2020-04-30-15:41
 */
class User {
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    private String name;
    private int age;

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

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

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

public class HashSet003 {
    public static void main(String[] args) {
        Set<User> set = new HashSet<>();
        User u1 = new User("zhangsan", 20);
        User u2 = new User("lisi", 30);
        set.add(u1);
        set.add(u2);
//在 u1的hashCode 位置上age=22，
        u1.setAge(22);
//删除是通过 new User("zhangsan",22)计算出的hashCode值去删除，此处不存在值，所以删除失败
        set.remove(u1); //false
        System.out.println(set);//[User{name='zhangsan', age=22}, User{name='lisi', age=30}]
//通过new User("zhangsan",22)计算出的hashCode值,在此hashCode位置上存值

        set.add(new User("zhangsan",22));
        System.out.println(set);//[User{name='zhangsan', age=22}, User{name='zhangsan', age=22}, User{name='lisi', age=30}]

//通过new User("zhangsan",20)计算出的hashCode值存值，虽然此处索引已存值，但是通过equals()比较出来的结果不相等，所以可以存入

        set.add(new User("zhangsan",20));
        System.out.println(set);//[User{name='zhangsan', age=22}, User{name='zhangsan', age=20}, User{name='zhangsan', age=22}, User{name='lisi', age=30}]



    }
}