CODEWITHSUNDEEP
javaclassparentmember
Xperiaz X
Xperiaz X

Reputation: 226

Data in Parent class

I have two classes A and B. in class A i create an object of B. From within the object x, I would like to access values of datamembers one and two. Is the only solution for that, passing it as parameter like

b=new B(one,two)

?. I donot want to extend, because class A is a frame and class B is a panel.

class A
{
    private int one;
    private String two;
    private myMethod()
    {
        B x=new B();
    }
}

Upvotes: 0

Views: 62

Answers (6)

Vincent van der Weele
Vincent van der Weele

Reputation: 13187

There are several ways you can go (I'll discuss each below)

  1. Pass the parameters one by one
  2. Pass the whole frame
  3. Extract an interface and pass that

Ad 1. This is the easiest approach, simply use a constructor like

public B(int one, String two) {
    ...
}

As you already mentioned, this is cumbersome if the number of parameters is large.

Ad 2. This is not a good idea. Does the panel really need to have access to all the properties of the frame? No, it doesn't. For instance you could:

public B(MyFrame a) {
    ...
    a.setVisible(false);
}

which is absolutely undesired. Besides, the problem with circular references is that you cannot make changes in isolation: changes to your frame can cause changes in the panel and vise versa.

Ad 3. This would be my preferred approach. You create an interface that provides exactly the functionality you need:

public interface MyInterface {
    public int getOne();
    public String getTwo();
}

Then you let your class A implement that interface:

public class A implements MyInterface {
    ...

    public int getOne() {
        return one;
    }

    public String getTwo() {
        return two;
    }
}

You know change the constructor of B to

public B(MyInterface a) {
    // use a.getOne() and a.getTwo() to get your data
}

And you can still create B from A as

B b = new B(this);

The three main advantages are:

  1. You need to pass only one parameter that contains all required data
  2. You don't expose more of class A than needed
  3. Class B does not explicitly depend on class A (only on interface MyInterface)

Upvotes: 1

c.s.
c.s.

Reputation: 4826

If classes A and B are separate components than I am afraid you don't have another choice.

If on the other hand class B belongs to class A in a functionality-wise manner you could make class B an inner class of A:

public class A {

    int one;

    class B {

        private void doSomething() {
            one = one + 1;   // inside B you can access memebers of A
        }
    }
}

Upvotes: 1

Santosh
Santosh

Reputation: 17923

Another way would be as follows: 

class B
{
   A a;
   public B(A a){
   this.a = a;
}
}

This will require that you have public accessor methods for the attributes of class A

Upvotes: 0

Prabhaker A
Prabhaker A

Reputation: 8483

You can delcare like this

    class B
   {
        private int one;
        private String two;

     // getter setters methods
   }

and call form Class A 's myMethod() should like thid

private myMethod()
{
    A a = new A();
    B b = new B();
    b.setOne(A.one);
    b.setTwo(A.two);
}

Upvotes: 0

Vadim
Vadim

Reputation: 2865

If you want one and two to be accessible outside of the class you can -

  1. Make them public
  2. Wrap them with a public property (a public get and a private set)

Then you can pass an instance of a (for example by using the this keyword) to the constructor of b;

Upvotes: 1

Ruchira Gayan Ranaweera
Ruchira Gayan Ranaweera

Reputation: 35587

class B
{
    private int one;
    private String two;
    public B(int one,String two) //constructor of B
    {
       this.one=one;
       this.two=two; 
    }

  // getter setters
}

If you create class B as above you can call B b=new B(one, two);

Upvotes: 1

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