How can I access methods or attributes from a subclass

[joshmo]

Hey all. Iam new to java and I have been trying to do something that has played me abit. I want to use an attribute or a method from a subclass and accesing it from the super class. Something like this

class A{
//some code
}

class B extends A{
public String a;

public String getMeth()
{
//
return something;
}

}

The above is just a sketch for illustration purposes. But what I want to do is to use the method or the attribute in the "class b" in A. Thanx for any help

[javaAddict]

You cannot use what you declare in B inside A.
Only the other way around since it is B that extends A, so B can access what you declare in A

[jbennet]

make the methods and fields public in the master class?

[stultuske]

make the methods and fields public in the master class?

making the superclass containing all the possible variables and methods of the classes that inherit it?

[joshmo]

You cannot use what you declare in B inside A. Only the other way around since it is B that extends A, so B can access what you declare in A

I know the other way round can be done. What about accesing the methods? I dont want to use overridding i dont know if there is a way using casting or polymorphism because that stuff is alittle confusing to me at the moment. Thanx

[javaAddict]

public class A {
   public void someMethod_A1() {

   }

   public void someMethod_A2() {

   }
}

public class B extends A {
   public void newMethod_B1() {
        //BOTH are the same:

         someMethod_A1(); //calls the method from super class
         super.someMethod_A1(); //exactly the same as the above
   }


// BUT if you also declare this:
    public void someMethod_A2() {

   }

//AND

    public void newMethod_B2() {
         this.someMethod_A2(); //calls the method from the class B (this class)

         super.someMethod_A2(); //calls the method from the class A (super class)
   }
}

I didn't quite understand what you are asking in your final post so I posted this example.
Let us know if you have any comments on it.

[joshmo]

I get that kind of calling. What i want to do is the other way round. I want to access the method in the subclass from the superclass. Is there any way this is possible?

[stultuske]

I get that kind of calling. What i want to do is the other way round. I want to access the method in the subclass from the superclass. Is there any way this is possible?

if I understand this correctly, you have (for instance) a class A (superclass) and a class B (subclass) which extends A, and you want B to be able to use a method in A?

just call it, you inherit the data and methods from A, so they're accessible for B

[joshmo]

if I understand this correctly, you have (for instance) a class A (superclass) and a class B (subclass) which extends A, and you want B to be able to use a method in A?

just call it, you inherit the data and methods from A, so they're accessible for B

That is not it. I want A to be able to use a method in B..Is that possible

[javaAddict]

You mean this? :

public class A {
   public void method_A1 {
      
        //calling method from B
        newMethod_B1(); 
   }
}

public class B extends A {
   public void newMethod_B1() {
       
   }
}

No it cannot be done. What I wrote above is wrong. Although however you can do this, but has nothing to do with inheritance:

public class A {
   public void method_A1 {
      
        B b1 = new B();
        b1.newMethod_B1(); 
   }
}

You can create and call any class from anywhere, but like I said it has nothing to do with one class extending the other

[stultuske]

you propably could code a way to do that, but what would be the use of that?

[joshmo]

Yep. That is what I was looking for. Thanks alot

[joshmo]

you propably could code a way to do that, but what would be the use of that?

well like I said am just tryna learn and satisfy my ego.

[Alex Edwards]

That is not it. I want A to be able to use a method in B..Is that possible

I think Object creation might shed some light on this issue...

If you create an Object of type A, A is at least of its class and additionally any other class it inherits from.

A cannot, at runtime, extend its static capabilities. Inheritance is resolved at compile time, so when A is defined and its super classes are known, objects of type A will not be able to do magical things like call methods (within the scope of A) that exist in a subclass that A isn't even aware of.

B on the other hand is at least of type B and additionally any other class it inherits from. B inherits from A so B can call methods that exist within the A class it is derived from.

If you want dynamic behavior where A can call B-like methods, you shouldn't rely on inheritance to do the trick and instead use a Pattern to solve the problem--

public class BaseClass{

	public void doSomething(){
		System.out.println("Do Something! O_O");
	}

}

public class DerivedClass extends BaseClass{

	public void moreWorkToDo(){
		System.out.println("Whoo! More work >_<");
	}

}

public class ModularClass extends BaseClass{

	public BaseClass myDynamicA = new BaseClass();

	@Override public void doSomething(){
		myDynamicA.doSomething();
	}

	public void setRef(BaseClass theRef){
		myDynamicA = theRef;
	}

	// I know this is sloppy, but it is an effective panacea for the situation
	public void callDerivedMethod(){
		if(myDynamicA instanceof DerivedClass){
			((DerivedClass)myDynamicA).moreWorkToDo();
		}
	}
}

Now you can treat ModularClass like 'A' with variable behavior, though the design can be much better such that this wouldn't be necessary.