Question

I think I’m misunderstanding something, and if so, I need help..

Let’s say I have the following two classes:

public abstract class Abstraction() {
   protected int number = 0;
   public void printNumber() {
       System.out.println(this.number);
       System.out.println(getNumber());
   }
   public int getNumber() {
       return this.number();
   }
}

public class Reality extends Abstraction {
   int number = 1;
   public Reality() {
       this.printNumber();
   }
}

// some other class
new Reality();

What should the output be? I’m getting 0, 0 (the code here is a bit more complicated but still the same issue).
How can I get the output to be 1,1?

Answer 1

The number in the Reality class doesn’t overwrite the number in the Abstraction class. Therefore, the Abstraction class still sees his own number value as 0.

A solution would be:

public class Reality extends Abstraction {
   public Reality() {
       number = 1;
       this.printNumber();
   }
}

Because your number in Abstraction is protected, you can access it in your Reality class.

---

Another example is a parameter in a method:

private int number;

public void myMethod(int number){
    number = 2;
}

Your private int number field won’t be set, instead, the parameter number will be set as 2.

---

Finally, a word on the this and super keywords, see an edit of your classes:

public abstract class Abstraction() {
   protected int number = 0;
   public void printNumber() {
       System.out.println(this.number);
       System.out.println(getNumber());
   }
   public int getNumber() {
       return this.number();
   }
}

public class Reality extends Abstraction {
   int number = 1;
   public Reality() {
       System.out.println(number); //Will print 1
       System.out.println(this.number); //Will print 1
       System.out.println(super.number); //Will print 0
   }
}