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Java OOP: how to use subclass object from superclass (this method has been overridden)

I have this example:

public class Inheritance {

    public static class Animal {        
        public void Scream() {
            System.out.println("I'm an animal");
        }       
    }

    public  static class Mammal extends Animal{
        public void Scream(){
            System.out.println("I'm a mammal");
        }       
    }

    public  static class Tiger extends Mammal{
        public void Scream(){
            System.out.println("I'm a tiger");
        }       
    }

    public static void main (String[] args){

        Animal tiger = new Tiger();
        tiger.Scream();
    }

}

Of course I will get: "I am a tiger". But I don't know how to type "I am a mammal" or "I am an animal".

@: and please answer my question: in the case of a class Tiger

What is a superclass from Tiger

. Mammal

or Animal

?

Please help me:)

Thank::)

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5 answers


When overriding a method, java always checks whose object was created at runtime. If you want to print "I am a mammal":

Animal m = new Mammal();
m.Scream();

this will print "I am a mammal".



And if you want to print "I am an animal":

Animal a = new Animal();
a.Scream();
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Here's some sample code:



public class Inheritance {

  public static class Animal {        
      public void Scream() {
          System.out.println("I'm an animal");
      }       
  }

  public  static class Mammal extends Animal{
      public void Scream(){
          super.Scream();
          System.out.println("I'm a mammal");
      }       
  }

  public  static class Tiger extends Mammal{
      public void Scream(){
          super.Scream();
          System.out.println("I'm a tiger");
      }       
  }

  public static void main (String[] args){
      Animal tiger = new Tiger();
      tiger.Scream();
  }

}
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Java is not like C ++ where possible.

You can call super.scream () on each scream method, but it will display both:

"I am a mammal" and "I am an animal".

I'm not sure why you would like to do this.

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To print "I am a mammal", you must make an object of the mammalian class.

 public static void main (String[] args){ 

    Animal mammal = new Mammal(); 
    mammal.Scream(); 
}

To print "I am an animal", you must make an object of class Animal.

 public static void main (String[] args){ 

    Animal animal = new Animal(); 
    animal.Scream(); 
}

NOTE. In both of these cases, the control variable remains Animal.

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1) As the other guys already said, call super.Scream()

if you want to call overridden method from superclass. You will have the following output:

I'm an animal
I'm a mammal
I'm a tiger

2) Tiger implements Mammal, so Mammal is a superclass of Tiger, and since Animal is a superclass of Mammal, Tiger also implements Animal. In other words: the tiger's super heads are tiger and animal.

// all of this is valid:
Tiger tiger = new Tiger();
Mammal mammal = tiger;
Animal animal = tiger;

If you call animal.Scream()

, the virtual machine knows that it anmial

is of type Tiger and calls the yell method declared in the Tiger class. See Polymorphism .

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