java中的==和equals()

package com.company;

public class Main {

    public static void main(String[] args) {

        Integer a1 = 1;
        Integer a2 = 1;
        System.out.println(a1 == a2);//trye
        System.out.println(a1.equals(a2));//true

        Integer a3 = 1;
        Integer a4 = 2;
        System.out.println(a3 == a4);//false
        System.out.println(a3.equals(a4));//false

        Integer a5 = new Integer(1);
        Integer a6 = new Integer(1);
        System.out.println(a5 == a6);//false
        System.out.println(a5.equals(a6));//true

        User user1 = new User("yanguobin", 22);
        User user2 = new User("yanguobin", 22);
        System.out.println(user1);//com.company.User@7a46a697
        System.out.println(user2);//com.company.User@5f205aa
        System.out.println(user1 == user2);//false
        System.out.println(user1.equals(user2));//false

        User user3 = new User("yanguobin", 22);
        User user4 = user3;
        System.out.println(user3);//com.company.User@6d86b085
        System.out.println(user4);//com.company.User@6d86b085
        System.out.println(user3 == user4);//true
        System.out.println(user3.equals(user4));//true
    }
}