Question

I have a JList component which should be emptied and repopulated. The following code (based on my original code) shows a simple window with a JList and a JButton:

import java.awt.BorderLayout;
import javax.swing.*;

public class JListTest extends javax.swing.JFrame{
    JList jList;
    JButton button;
    DefaultListModel model;

    public JListTest() {
        jList = new JList();
        model = new DefaultListModel();
        jList.setModel( model );
        button = new JButton();

        getContentPane().add(jList, java.awt.BorderLayout.CENTER);

        button.setText("add 10000 items");
        button.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                model.clear();
                for( int i=0; i<10000; ++i ) {
                    model.addElement( "aaaa");
                }
            }
        });
        getContentPane().add(button, BorderLayout.PAGE_START);        
        pack();        
    }

    public static void main(String args[]) {
        JListTest jlt =new JListTest();
        jlt.setSize(300, 300);
        jlt.setVisible( true );
    }
}

If I press the button the insertion (10000 items) is very fast. If I press it again and again it is still very fast.

If I select the third item and press the button, the result is the same, the insertion is very fast.

If I select the first item and press the button, the program becomes very slow (actually I have to stop it).

Why the selection of the first item slows down the execution?

I’ve tested it using JDK 1.5 and 1.6.

Answer 1

I’d suggest to write your own model which allows to add a bunch of values at once. I guess it’s not the addition to the model but the GUI things triggered by this that kill the performance.