🚀 go-pugleaf

Hello Michael,

I try your example within Jbuilder3 Field Test3 without the pb you
encountered.

Hope this help !

Michael Boyle wrote:

> I have been unsuccessfully attempting to implement the singleton
> pattern in my project.  A short example demonstrating the problem
> appears below.  My environment is JBuilder 2.01 with
> JDK1.1.6_Borland.
>
> I have a class (see "TestApp") below, which stores a reference
> to its sole instance as a private static data member.
>
> The main() function causes this static member to be initialized,
> and its constructor creates and displays a window with a
> small menu.
>
> After hitting the menu buttons a few times, you will see (I hope)
> that THE FINALIZE METHOD FOR TestApp IS CALLED!!!!
>
> Now, I realize that no object is storing a reference to my
> TestApp instance, but surely any static member object of a
> class should not be garbage collected.
>
> What's going on here?  Is this a JBuilder problem, a JDK problem,
> or a "feature" of Java?  If in fact static class members can
> be arbitrarily garbage collected, then how can the Singleton
> pattern be implemented in Java?
>
> I'd be interested to know if this occurs with other versions
> of JBuilder or the JDK.
>
> //-----------------------------------------------------
> // file TestApp.java
>
> import java.awt.event.*;
> import com.sun.java.swing.*;
>
> public class TestApp {
>
>   private static TestApp app = null;
>
>   private TestApp() {
>     TestWin w = new TestWin();
>   }
>
>   protected void finalize() {
>     JOptionPane.showMessageDialog(null, "TestApp finalized");
>   }
>
>   public static TestApp getInstance() {
>     if (app == null) {
>       app = new TestApp();
>     }
>     return app;
>   }
>
>   public static void main(String[] args) {
>     TestApp.getInstance();
>   }
> }
>
> //-----------------------------------------------------
> // file TestWin.java
>
> import java.awt.*;
> import java.awt.event.*;
> import com.sun.java.swing.*;
>
> public class TestWin extends JFrame {
>
>   public TestWin() {
>     enableEvents(AWTEvent.WINDOW_EVENT_MASK);
>     this.getContentPane().setLayout(new BorderLayout());
>     this.setSize(new Dimension(400, 300));
>     this.setTitle("Singleton Test");
>
>     JMenu menu = new JMenu("File");
>     menu.add(new JMenuItem("Button 1"));
>     menu.add(new JMenuItem("Button 2"));
>
>     JMenuBar mb = new JMenuBar();
>     mb.add(menu);
>     this.setJMenuBar(mb);
>
>     validate();
>     setVisible(true);
>   }
>
>   protected void processWindowEvent(WindowEvent e) {
>     super.processWindowEvent(e);
>     if (e.getID() == WindowEvent.WINDOW_CLOSING) {
>       System.exit(0);
>     }
>   }
> }