Re: object interaction

From:

Andy Flowers <no.way@hose.com>

Newsgroups:

comp.lang.java.help

Date:

Fri, 19 May 2006 09:10:34 GMT

Message-ID:

<eYfbg.15074$z%.14314@newsfe5-win.ntli.net>

linuxnooby@yahoo.com.au wrote:

Hi

I need some help with this one.

I instantiate an object "a", of class A.
Within that object another object "gui", of class GUI, is instantiated.

object "a" can access the methods of object "gui", but I cannot get
object "gui" to access the methods of object "a"

For example user input might trigger an event that requires "gui" to
call a method from the main application . In the example below i have
put message(a); in to trigger the event to keep it simple. But I
cannot figure out how to give "gui " a handle on "a"

cheers Dave

class Gui{

    Gui(){

        message(a);
    }
    public void message(A a){

    a.doessomething();
    }
}

public class A {
    public A() {

        Gui gui = new Gui();
    }

    public void doessomething(){
    System.out.println("hello world");
    }

    public static void main(String[] args) {
        A a = new A();
    }
}

Pass the instance of A you want to be worked on to the instance of Gui

You need a constructor in Gui that takes and instance of A as a parameter and
[maybe] a place to store this in Gui.

i.e.

class Gui
{
    private A myLocalA = null; // this is needed if we want to keep a
                                // relationship

    Gui(A a)
    {
      myLocalA = a;

      message(a);
    }
}

public class A {
     public A() {
         // instantiate a Gui with me
         Gui gui = new Gui(this);
     }

     public void doessomething(){
     System.out.println("hello world");
     }

     public static void main(String[] args) {
         A a = new A();
     }
}

You need to be very careful with this as calling methods on A from the
constructor of Gui, which is created in the constructor of A may mean that the
instance of A is not fully initialised as per your application logic etc.