Question

I am trying to create a custom event which listens and responses to the clicks of a button. The button is represented as an oval, drawn in a paintComponent method on shown in a JFrame. When it is clicked, it is supposed to change colour, then return to a previous colour when clicked again – like an ON / OFF button.

I have created an interface for it:

public interface gListener {
    public void gActionPerformed(GooEvent e);
}

An event listener:

public class gEvent extends java.util.EventObject
{
    private int x, y;
    private int value;
    private gComponent source;
    final static int ON = 1;
    final static int OFF = 0;

public gEvent(int x, int y, int val, gComponent source)
{
    super(source);
    this.x = x;
    this.y = y;
    value = val;
    this.source = source;
}
}

A component class to represent the button:

public abstract class gComponent {

    //Link an arraylist to the gListener interface.
    ArrayList <gListener> listeners = new ArrayList<gListener>();
    int x, y, w, h;

    public gComponent(int x, int y, int w, int h) {
        this.x = x; this.y = y; this.w = w; this.h = h;
    }

//Add listener to arraylist
    public void addListener(gListener gl)
    {
        listeners.add(gl);
    }

    // Dispatches the gEvent e to all registered listeners.
    protected void send (gEvent e){
        e = new gEvent(x, y, w, this);
        Iterator<GooListener> i = listeners.iterator();
        while (i.hasNext())  
        {
            ((gListener) i.next()).gActionPerformed(e);
        }
    }
}

The gComponent class is extended in a button class (gButton), which is where the paintComponent and mouseClicked methods are called. And lastly… I have the test class which extends a JPanel and implements the gListener interface. The main method looks like the following:

public static void main(String[] args) {
        // JFrame code goes here....


        gButton button = new gButton(20,20,20,20); //Click oval shape

          //Using addListener method from gComponent superclass.
          //The 'this' code is throwing error: cannot use this in a static context.
        button.addListener(this); 
}

  //Cause something to happen - stop/start animation.
    public void gooActionPerformed(GooEvent e){


    }

The event is suppose to trigger from a click of the button, in this particular format of how I have written the code.
Any advice to the error I received as stated in my test class, or anything else would be much appreciated. Many thanks.

Answer 1

This is simply… breathtaking.

But in any case, there’s no this in a static method like main(). If you want an object with a gooActionPerformed() method, then you need to create an instance of whatever class main() appears in, and use that instance in place of this.