Java Inheritance super keyword use

chima
chima used Ask the Experts™
on
Hello,
Without showing the entire code, I hope to explain what I'm expecting to get answered.
I have initialized a and b, in the parent class.  In the sub class "classB" it is extended by classA.
In classB, as shown below, I can re-initialize a and b (at least I think it is the a and b from classA), if they are from classA.
 I would not want to re-initialize a and b in classB, but I have no choice (error occurs if I do not initialize them).  what I would like to see from super.m3(), in the println statement; are the values given to a and b within the parent class (classA).
Might you know how to do this;
class classB extends classA{
	
		public int c;  public int d;
		public void m3(){
			super.b=4;
			super.m3();
			super.a=5;
			
			System.out.println("This is classB super m3" +  " " + "a & b are initilized in ca: " + a + b + c + d + "\n");		
		}

Open in new window


thanks
Comment
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
Top Expert 2015

Commented:
U need to share the m3 method in the superclass.

Author

Commented:
Parent class is;
class classA{	
		public int a; 	public int b;  
		public void m1(){
			System.out.println("This is classA m1" +  " " + a + b + "\n");
		}
		
		public void m3(){
			//super.m3();
			System.out.println("This is classA m3:" + " " + a + " " + b + "\n");			
		}
	}

Open in new window

If you don't initialize them you should be fine to still call m3() and they will print out as having value 0 - which is the default value for an int that you have not explicitly set.

		public void m3() {
                        // Don't initialize
			//super.b = 4;
			//super.a = 5;

			super.m3();

			System.out.println("This is classB super m3" + " " + "a & b are initilized in ca: " + a + b + c + d + "\n");
		}

Open in new window


You should get:

This is classA m3: 0 0

This is classB super m3 a & b are initilized in ca: 0000

As the output.

Doug
Ensure you’re charging the right price for your IT

Do you wonder if your IT business is truly profitable or if you should raise your prices? Learn how to calculate your overhead burden using our free interactive tool and use it to determine the right price for your IT services. Start calculating Now!

Author

Commented:
Doug, correct, if I do not initialize a & b, I do get 0 0.  The situation is that I do initialize a & b, and when I get to classB extended by cla
classA, I want to display a & b of the parent class; which should be a=1, and b=2;

	class classB extends classA{
	
		public int c;  public int d;
		public void m3(){
			//super.a=8;			
			//super.b=9;
			super.m3();

The code below is after public static void main(String args[])
                         ca.a=1;
			ca.b=2;
			ca.m1(); // 1 2
			ca.m3(); // 1 2
			
			cb.c=3;
			cb.d=4;
			cb.m3();

Open in new window

You need to give us an example of the problem and a clear statement of what you're expecting to happen.  I'm still a bit confused.

E.g. Here is a full working example that you can run:

public class ClassTest {
	public static void main(String[] args) {
		classB ca = new classB() ;
		ca.a = 1 ;
		ca.b = 2 ;
		ca.m3();
	}

	public static class classA{
		public int a; 	public int b;
		public void m1(){
			System.out.println("This is classA m1" +  " " + a + b + "\n");
		}

		public void m3(){
			//super.m3();
			System.out.println("This is classA m3:" + " " + a + " " + b + "\n");
		}
	}

	public static class classB extends classA {

		public int c;
		public int d;

		public void m3() {
			//super.b = 4;
			//super.a = 5;
			super.m3();

			System.out.println("This is classB super m3" + " " + "a & b are initilized in ca: " + a + b + c + d + "\n");
		}
	}
}

Open in new window


This code outputs:

This is classA m3: 1 2

This is classB super m3 a & b are initilized in ca: 1200

Is this the code you want to run?  Is this the output you expect?

Please modify this code (i.e. a full working example) and explain what part of this isn't what you're looking for and we can probably help explain it to you.

Doug

Author

Commented:
Doug, I apologize.  Here is what I just figured out, and it is probably what you have been telling me.
This is the entire code.  What I learned is that public  int a, b, c, and b declared within the Class but not inside the method, cannot be displayed from the super.method.  They can be displayed within its own method.  To display the variable from a super.method, the variable has to be initialized within the method.  The super.method can be overloaded.
Let me know if I did not explain this to your understanding;

	class classA{	
		public int a; 	public int b;  // Can't get to these variables
		public void m1(){
			a=14; b=15; 
			System.out.println("This is classA m1: " +  " " + a + " "+ b + "\n");
		}
		
		public void m3(){
			a=12; b=13;
			//classA.this.a;
			//System.out.println("This is classA m3:" + " " + a + " " + b + "\n");			
		}
		
		// Overloading
		public void m3(int aa, int bb){
			a=aa; b=bb;
			System.out.println("This is classA m3:" + " " + a + " " + b + "\n");			
		}
	}

	class classB extends classA{	
		public int c;  public int d;
		public void m3(){
			//super.a=8;			
			//super.b=9;
			//this.a;
			
			super.m3();
			System.out.println("This is classB super m3" +  " " + "a & b are initilized in ca: " + this.a + " " + b + " " + c +" "+ d + "\n");		
		}

		public void m4(){
			//super.m3();
			//System.out.println("This is classB m4 SUPER m3" + " " + a + " " + b + "\n");	

		}
	}
	
	// Multi Inheritance
	class classTest extends classB{
		public void m1(){
			super.m1();
			//System.out.println("This is classTest m1,m2,m3,m4" + " " + super.a + this.b + this.c + this.d + "\n");
		}
		
		public void m5(){
			//System.out.println("This is classTest m5" + " " + classTest.this.a + b + c + d + "\n");
		}
	}
	
	public class Inheritance {	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
			classA ca=new classA();
			classB cb=new classB();
			classTest ct=new classTest();
			
			ca.a=1;
			ca.b=2;
			ca.m1(); // 1 2
			ca.m3(); // 1 2
			ca.m3(20,30);
			
			cb.c=3;
			cb.d=4;
			cb.m3();
			
			ct.m1();
			//ct.clasTest();			
	}

}

Open in new window

Yes it sounds like you've figured this out for yourself.

Author

Commented:
thanks

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial