When using polymorphism, two ideas to judge whether it can be transformed downward

When using polymorphism , Two ways to judge whether it can be transformed downward

1 Use instanceof keyword

1.1 The core idea

Determine whether the object is an instance of a class ( Such as animal01 Whether it is Dog Generated by instantiation )

1.2 Sample code

Animal class

package Work;
public class Animal {
    
    private String name;
    // full name 
    private int age;
    // Age 

    public Animal() {
    
    }

    public Animal(String name, int age) {
    
        this.name = name;
        this.age = age;
    }

    public String getName() {
    
        return name;
    }

    public void setName(String name) {
    
        this.name = name;
    }

    public int getAge() {
    
        return age;
    }

    public void setAge(int age) {
    
        this.age = age;
    }
}

Dog class

package Work;
public class Dog extends Animal{
    
    public Dog() {
    
    }

    public Dog(String name, int age) {
    
        super(name, age);
    }
    public void guardDoor(){
    
        System.out.println(" The dog is watching the door ");
    }
}

Test class

package Work;
public class Test {
    
    public static void main(String[] args) {
    
       Animal animal01=new Dog(" Wangcai ",10);
       if (animal01 instanceof Dog){
    
           ((Dog) animal01).guardDoor();
       }
    }
}

1.3 Screenshot of sample code operation

2 Use getclass() Method

2.1 The core idea

Judge whether the class that generates the object is a class ( Such as animal01 Whether it is Dog Generated by instantiation )

2.2 Sample code

Animal class

package Work;
public class Animal {
    
    private String name;
    // full name 
    private int age;
    // Age 

    public Animal() {
    
    }

    public Animal(String name, int age) {
    
        this.name = name;
        this.age = age;
    }

    public String getName() {
    
        return name;
    }

    public void setName(String name) {
    
        this.name = name;
    }

    public int getAge() {
    
        return age;
    }

    public void setAge(int age) {
    
        this.age = age;
    }
}

Dog class

package Work;
public class Dog extends Animal{
    
    public Dog() {
    
    }

    public Dog(String name, int age) {
    
        super(name, age);
    }
    public void guardDoor(){
    
        System.out.println(" The dog is watching the door ");
    }
}

Test class

package Work;
public class Test {
    
    public static void main(String[] args) {
    
       Animal animal01=new Dog(" Wangcai ",10);
       if (animal01.getClass()==new Dog().getClass()){
    
           ((Dog) animal01).guardDoor();
       }
    }
}

2.3 Screenshot of sample code operation