Understanding of object

One 、object Class summary
1.object Feature 1 ：
object It can solve the problem of parameter unification , in other words object Parameters of all data types can be accepted .

 Object o=new Person1();// Upward transformation 
  /** * instanceof  see o Is it right? Person1 Instantiation  */
 if(o instanceof Person1){
    
            Person1 per=(Person1)o;
            System.out.println("Person The downward transformation was successful ");
        }
class Person1 extends Object{
    }
// result ：Person The downward transformation was successful  

2.object Two commonly used functions of
(1)toString
toString yes ptintln The method that will be called by default , So we usually export toString Omit
toString stay Object Generally, the address value of the object is directly different , The name of the output class [email protected]+16 Hexadecimal hash code, such as ：

Person1 pa=new Person1(" Fu Jiayue ",23);
System.out.println(pa);
cn.tedu.exercise.Person1@2519ca98

So if we want to output the attributes of the object directly , We need to rewrite in the corresponding class toString Methods （ stay idea Can be directly Generate->toString), But if we want to be in Person1 Rewriting in toString The method is also very simple ：

public String toString(){
    
        return "name"+name+"age"+age;
    }

(2)equals
equals stay Object By default == The way ：
== Generally, there are two types , If there are data classes before and after , Our comparison is numerical , If it's an object , Our comparison is the address value . Data types are left aside , Let's take the object as an example ：

 Person1 pa=new Person1(" Fu Jiayue ",23);
 Person1 pb=new Person1(" Fu Jiayue ",23);
 System.out.println(pa.equals(pb));

The result is ：

false

If we want to judge whether the properties of two objects are equal , We must rewrite equals Method （ stay idea Can be directly Generate->equals() and hashcode() Generate equals Method ）, If we want to rewrite equals Methods can refer to the following methods , Of course, the method is not just one .

class Person1 extends Object{
    
    String name;
    int age;
    @override
    public boolean equals(Object obj){
    
       /** *  Judge whether the two are the same class , such as pa.equals(" Dog ") */
     	 if(!(obj instanceof Person1)){
    
            return false;
        }
        /** *  Judge whether the incoming object is empty, that is null, In this case, a null pointer error will occur  */
        if(obj==null){
    
            return false;
        }
        /** *  Judge whether they are the same object  */
        if(this==obj){
    
            return true;
        }
        Person1 per = (Person1) obj;//obj There's no person Properties of , In order to obtain person Properties of 
        return this.name.equals(per.name)&&this.age==per.age;
    }