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Tip of the Day
Language: Java
Expertise: Intermediate
Mar 19, 2001

Catching Events


If you are looking for a way to catch events every time a Swing text field changes, there is an easier way than listening for regular document events. It's pretty simple to define a subclass of the PlainDocument class (the standard data class for text fields) that can run your event code directly:
 
import javax.swing.text.*;
import javax.swing.event.*;
 
public class TriggerDocument extends PlainDocument {
    private Runnable runable = null;
 
    public TriggerDocument(Runnable run) {
        super( );
        runnable = run;
    }
 
    protected void fireEvent( ) {
        if (runnable != null)
            runnable.run( );
    }
    protected void fireChangedUpdate(DocumentEvent e) {
        super.fireChangedUpdate(e);
        fireEvent( );
    }
    protected void fireInsertUpdate(DocumentEvent e) { 
        super.fireInsertUpdate(e);
        fireEvent( );
    }
    protected void fireRemoveUpdate(DocumentEvent e) { 
        super.fireRemoveUpdate(e);
        fireEvent( );
    }
}

So, when you create your text field, set the document to the trigger document passing the code you need to be executed every time the user adds, replaces or removes data in the text field:
 
    JTextField txt = new JTextField( );
    txt.setDocument(new TriggerDocument(new Runnable( ) {
        public void run( ) {
            someMethodInYourMainClass( );
        } } ) );
Andy Brundell
 
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