Java重写equals方法和hashCode方法

package com.ddy;

public class User {
    private Integer id;

    private String name;

    private String address;

    private String phone;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name == null ? null : name.trim();
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address == null ? null : address.trim();
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone == null ? null : phone.trim();
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.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;
        User other = (User) obj;
        if (id == null) {
            if (other.id != null)
                return false;
        } else if (!id.equals(other.id))
            return false;
        return true;
    }

    public User(Integer id) {
        super();
        this.id = id;
    }

}

Person根据id重写了equals和hashCode方法；这样HashSet添加people的时候会将id重复的people对象视为同一个people对象。

package com.ddy;

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

public class Test {
    public static void main(String[] args) {
        User user1 = new User(1);
        User user2 = new User(1);
        Set<User> users = new HashSet<>();
        users.add(user2);
        users.add(user1);
        System.out.println(users);
    }
}

输出结果：[com.ddy.User@20]