CODEWITHSUNDEEP
javainheritance
Raghu Veer
Raghu Veer

Reputation: 3

why can't we access parent class instance variables inside the class outside the method in child class in java?

class Demo1{
  int age=12;
  public void display(){
   System.out.println("InDemo1");
  }
}

class Demo2 extends Demo1{
    age=19;   **//------------------->getting error here**
    @Override
    public void display(){
        
        System.out.println("InDemo2"+age);
    }
    public Demo2(){
      System.out.println("Inside the constructor");
    }
}


public class SuperKeyword {
    public static void main(String[] args){
        Demo2 demo2=new Demo2();
        demo2.display();
    }
}

I getting compile time error in class Demo2 by using super.age (or) creating a object of Demo1 and acessing the age variable is also giving me compile time error like unidentified token.

I tried to modify the inherited age variable from Demo1 inside the method or constructor in Demo2 class, it is working but, I can't understand we can't we accessed outside the method or constructor in demo2 class

public class SuperKeyword {
    public static void main(String[] args){
        Demo2 demo2=new Demo2();
        demo2.display();
    }
}
class Demo1{
    int age=12;
    public void display(){
        System.out.println("InDemo1");
    }
}

class Demo2 extends Demo1{
    public void display(){
        super.age=19;  //---------->not getting error
        System.out.println("InDemo2"+age);
    }

Upvotes: 0

Views: 286

Answers (1)

Thomas
Thomas

Reputation: 88707

That age=19; is outside of any method or initializer block and thus would need to be a variable declaration like int age=12;. Note that during variable declaration you may define an initial value but you don't have to, i.e. int age; would be fine too.

What you want to do is set a new value when the instance is initialized which is what initializer blocks are for:

class Demo2 extends Demo1 {
  //this is an instance initializer block      
  {
    age=19;
  }

  //rest of your code
}

Initializer blocks are executed before the constructor for the respective class in the hierarchy, i.e. in the case above the order would be:

  • Demo1() constructor
  • { age=19; } block
  • Demo2() constructor

Also note that you can add the static keyword to an initializer block in which case it is executed once when the class is loaded.

Upvotes: 2

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