How to call methods from other classes not having an instance?

Question

How can I call a method from a class that is not an object within another class, and has nothing in common with this other class?

In my case:

class GridUI {
    com.google.gwt.user.cellview.client.DataGrid grid;

    public void refresh() {
         dataGrid.redraw();
    }
}

class SomeBackendService() {
   public foo() {
      //have to trigger refresh of a specific grid
   }
}

One possibility might be to make the refresh() and grid static . But that's bad design, and I cannot use this approach as I want to use several implementations of GridUI .

So, how can I refresh a certain gridclass in my app from any service that does not contain this grid as an object??

Answer 1

Just create and fire an Event for it in your service and make your grid register for that Event . It's probably best to use an EventBus .

Using a static Map<String, Grid> as was suggested in the accepted answer will work but it's not proper. You risk making mistakes and it's not as easy to manage when the number of grids increases.

The EventBus approach is more work upfront but in the end it's a better approach. You'll be able to reuse the EventBus throughout your application. It really helps keep your coupling down. You'll also easily be able to get different objects act on the same Event with little effort.

Answer 2

Alternatively create a components registry (basically a Map<String,Grid> ), then fetch the grid from SomeBackendService using its id as key in the registry. (I guess you know which grid you want to refresh, right?)

Be careful with registries though:

• make sure they are thread safe if need be (probably true in an UI app)
• they tend to fill up and leak memory if not properly handled

Answer 3

Sorry for not answering that long time, i was in vacation.

Interfaces are some kind of classes. But they do not implement any method, they have empty method bodies.

Each class, which implements an interface usually MUST implement its methods.

In C# You would Do :

enter code here

    interface IMyInterface
    {
       void PleaseImplementMe();
    }


    class clMyInterface :IMyInterface
    {

        void  IMyInterface.PleaseImplementMe()
        {
            MessageBox.Show("One implementation");
        }    
    }





end

Please let me know, whether this is what can help You or not.