重写equals方法

前言：

重写equals方法能够学习到多态、instanceof

代码实现：

public class Super{
    public static void main(String[] args) {
        Super.User1 user1 = new Super.User1();
        Super.User2 user2 = new Super.User2();
        System.out.println(user2.equals(user1));
    }
    interface IUser{
        int number = 0;
        String name = "里斯";
        public void doing();
        public void toDo();
    }
    static class User1 extends User2{
        private int studentId = 1342432423;
        private String studentClass = "二班";

        public int getStudentId() {
            return studentId;
        }

        public void setStudentId(int studentId) {
            this.studentId = studentId;
        }

        public String getStudentClass() {
            return studentClass;
        }

        public void setStudentClass(String studentClass) {
            this.studentClass = studentClass;
        }

        public void doing(){
            System.out.println("User1类正在做");
        }
        public void toDo(){
            System.out.println("User1类已经做过");
        }
    }

    static class User2 implements IUser{
        private int studentId = 1342432423;
        private String studentClass = "二班";

        public int getStudentId() {
            return studentId;
        }

        public void setStudentId(int studentId) {
            this.studentId = studentId;
        }

        public String getStudentClass() {
            return studentClass;
        }

        public void setStudentClass(String studentClass) {
            this.studentClass = studentClass;
        }

        public void doing(){
            System.out.println("User2类正在做");
        }
        public void toDo(){
            System.out.println("User2类已经做过");
        }
        //使用Object的原因是它是所有类的父类,于是有了Obejct obj = new User1();把User1类向上转型为obj对象
        public  boolean equals(Object obj){
            //如果比较的是自己本身
            if(obj == this){
                return true;
            }
            //考虑到程序的健壮性，在方法的形参是引用类型的时候，建议做非null处理
            if(obj == null){
                return false;
            }
            // 两个对象的类型都不一致，对象肯定不一致
            if (getClass() != obj.getClass())
                return false;

            if(obj instanceof User2){
                //将obj对象向下转型为User2类
                User2 user = (User2) obj;
                //这里添加我们想要判断的条件
                if(this.getStudentClass().equals(user.getStudentClass()) && this.getStudentId() == user.getStudentId()){
                    //studentClass和studentId都相等的情况下
                    return true;
                }
            }
            return false;
        }

    }

}

总结：

instanceof左边必须是右边的类或者是子类的实现对象