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]