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Scrollbars AND Buttons

Dirk Schreckmann
Sheriff

Joined: Dec 10, 2001
Posts: 7023
How do I 'implement' both the ActionListener and the AdjustmentListener in one class? I'm trying to simply have a Scrollbar and a Button in one class, but I only know to program for one or the other type per class.
Yes, I am a beginner.
Thank you for your help.

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matt hooker
Ranch Hand

Joined: Jul 26, 2001
Posts: 46
Classes can implement multiple interfaces/listeners. just do like Class blah() implements listenerA, listenerB {


Its not what you do, its the way you say you've done it.
Dirk Schreckmann
Sheriff

Joined: Dec 10, 2001
Posts: 7023
Thank You
rom chatterjee
Ranch Hand

Joined: Dec 11, 2001
Posts: 46
Previous answer perfectly correct. To complete the contract you have to implement the actionPerformed and adjustmentListener methods (as I am sure you are aware).
However if you have lots of buttons (you're not likely to have many scrollbars), you're actionPerformed method will have to identify which button was pressed and then take action. The problem with tihs is 2 fold:
1. The actionPerformed part of your code can be far removed from your button implementation.
2. Your actionPerfromed method can be quite large.
This is just awkward in terms of your code being easy to read and knowing what happens when an event occurs.
Another approach is to use an anonymous class. This is easier than it sounds. The code would look something like this:
Button okButton = new Button("OK");
okButton.addActionListener(/*anonymous inner class*/);
The next bit is to add the anonymous inner class. The code for the class is:
new ActionListener(){
public static void actionPerformed(ActionEvent e){
//...do something when okButton pressed
}
}
This has 2 parts. First create a new object - new ActionListeneter(), followed by the implementation of the actionPerformed method
okButton.addActionListener(new ActionListener(){
public static void actionPerformed(ActionEvent e){
//... do something here
}//end actionPerformed efinition
}//end anonymous class definition
);//end addActionListener method call
Your code doesnt need this kind of spacing or comments but I just did it this way to help make it easy to see what bracket is closing which part of code.
This approach mena you can add a whole range of event handlers at point of use
Rom


Rom Chatterjee<BR>Sun Certified Java Programmer
 
With a little knowledge, a cast iron skillet is non-stick and lasts a lifetime.
 
subject: Scrollbars AND Buttons