confusion in the output

[jayalakshmi charugundla]

Hi,

The following program's output is 40 but as I know the answer would be 30. Why it's giving 40 instead of 30?
Please explain this

 

class Base{
        int value = 0;
        Base(){
        addValue();
        }
        void addValue(){
        value += 10;
        }
       int getValue(){
         return value;
       }
     }
    class Derived extends Base{
      Derived(){
       addValue();
      }
     void addValue(){
     value +=  20;
      }
    }
    public class Test {
      public static void main(String[] args){
          Base b = new Derived();
          System.out.println(b.getValue());
      }
    }

   

Thanks in advance
jaya

[Vijitha Kumara]

How many times the "addValue()" method being invoked upon creating a "Derived" instance ?

[Nathan Warner]

The reason the value is 40 instead of 30 is because it uses the Derived class version of the addValue method in both calls so it is 20+20 which is 40 instead of the 20+10. This deals with the method being overridden in the subclass.

[Ankur kothari]

   

class Base{
        int value = 0;
        Base(){
			System.out.println("1");
        addValue();
		System.out.println("2");
        }
        void addValue(){
			System.out.println("3");
        value += 10;
        }
       int getValue(){
         return value;
       }
     }
    class Derived extends Base{
		int value=10;
      Derived(){
		  System.out.println("4");
       addValue();
	   System.out.println("5");
      }
     void addValue(){
		 System.out.println("6");
     value +=  20;
      }
	  int getValue(){
         return value;
       }
    }
    public class Test22 {
      public static void main(String[] args){
          Derived b = new Derived();
          System.out.println(b.getValue());
      }
    }

     

why is the output in this case 30 and not 50? isnt addValue() called two times?

[Ankur kothari]

when a class is loaded all its instance variables are given their default values like int will get 0 etc....

[Ankur kothari]

   

class Base{
        int value = 20;
	{
		System.out.println("7");
	}
        Base(){
			System.out.println("1");
        addValue();
		System.out.println("2");
        }
        void addValue(){
			System.out.println("3");
        value += 10;
		System.out.println(value);
        }
       int getValue(){
         return value;
       }
     }
    class Derived extends Base{
		int value=10;
		{
		System.out.println("8");
	}
      Derived(){
		  System.out.println("4");
       addValue();
	   System.out.println("5");
      }
     void addValue(){
		 System.out.println("6");
		  System.out.println(value);
     value +=  20;
	 System.out.println(value);
      }
	   int getValue(){
         return value;
       }
	 
    }
    public class Test22 {
      public static void main(String[] args){
          Derived b = new Derived();
          System.out.println(b.getValue());
      }
    }

     

study this example which will clear all your doubts.......

[jayalakshmi charugundla]

Thank you Ankur. You have explained it very well.