Ready to test your coding knowledge?

In this article, I challenge you to examine two Java Swing examples, specifically using threads. Each are wrong, in a subtle but painful way.

See if you can identify the problem before I show you the best way to correct the offending code.

Let's start with a thread blocking example.

I created a simple Swing class file. I am sure this is extremely common. On the surface, it looks perfectly acceptable. In this class, I extend from a JFrame and add a simple button to the frame.

Take a look at the code, and see if you can spot the issues:

package com.zarrastudios.example;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class FrameExample1 extends JFrame {
  private JButton btnActivate;

  public FrameExample1() {
    super("Frame Example 1");
    initAndLayoutComponents();
    initListeners();
    pack();
  }

  private void initListeners() {
    btnActivate.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent event) {
        //Simulate database access
        try {
          Thread.sleep(100000);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
      }
    });
  }

  private void initAndLayoutComponents() {
    btnActivate = new JButton("Activate");

    JPanel main = new JPanel(new BorderLayout());
    JPanel north = new JPanel(new FlowLayout());
    JPanel center = new JPanel();

    center.setBackground(Color.pink);

    north.add(btnActivate);

    main.add(north, BorderLayout.NORTH);
    main.add(center, BorderLayout.CENTER);

    setContentPane(main);
  }

  public static void main(String args[]) {
    FrameExample1 fe1 = new FrameExample1();
    fe1.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent event) {
        System.exit(0);
      }
    });
    fe1.setVisible(true);
  }
}

I'll give you the answers on the next page. But before you move forward, do your best to identify the problem.