import javax.swing.JFrame;
import javax.swing.JLabel;
import java.awt.EventQueue; 

public final class HelloWorld implements Runnable {

    public static void main(String[] args) {

        // Swing has its own dispatch thread, which is 
        // distinct from the main JVM (launcher) thread.  
        // This means that even if the (launcher) thread exited 
        // (this) main method, the Swing GUI thread would
        // still be running, waiting to respond to user input, etc.
        // and if the user closes the window, then the program would
        // continue to run (due to the live gui thread). As of Java 6, the
        // GUI thread will automatically stop if all Components are hidden and
        // disposed.
        //
        // Execute all GUI code on the event dispatch thread, even initialization:

        EventQueue.invokeLater (new HelloWorld());
    } 

    public void run() {

        // Create frame with title "Hello, World!"

        JFrame f = new JFrame ("Hello, World!");

        // Previously we typically attached a window listener to our main JFrame
        // and on windowClosing() event notification callback, we would
        // explicitly call System.exit(stat) or some other such nastiness.
        // The following is the new (clean) way of defining default close behavior
        // for a JFrame.  The following will merely dispose the JFrame but it will not
        // stop the application unless *all* Windows are disposed.

        f.setDefaultCloseOperation (JFrame.DISPOSE_ON_CLOSE);

        // this stops the app on window close
        // (it is commented out.)
        //            f.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        // JFrame, which is the 'window' component of Swing, has an interesting feature:
        // it has a layered content architecture which (conceptually) allows for placement
        // of a component of the JFrame in a designated layer.  The layers can be conceptually
        // viewed as a series of transparencies placed one above another in an overhead 
        // projector.
        // Swing typically places user components (such as buttons, etc.) in what it calls its
        // 'content pane'.  This pane is layer that is below most of the other (transparent)
        // layers.  What are the layers for?  Think of when you right-click on a control and it 
        // 'pops' a contextual menu 'over' the original control; or, when you press 'help' for 
        // a control or hover the mouse for a 'tool tip' and the information is 'placed over 
        // the control'.  How is that done?  By rendering the information in a layer 'above' 
        // the lower level 'content' pane.
        // So:
        // The standard way of adding a component to a 'multi-pane' container such as JFrame is
        // by first establishing a reference to its 'content pane' (which is, by default just a 
        // JPanel with BorderLayout and adding the components the JFrame to the content pane 
        // and NOT directly to the JFrame.  (The latest Swing release however alters the         
        // semantics of the JFrame.add(..) to assume convenient addition to the content pane).
 
        f.getContentPane().add (new JButton("<html>hello<br>world"));
 
        // Remember the relative layouts of Swing?  
        // pack() tells the receiving container (here 'this' JFrame)
        // for it to optimally pack its components according to its layout.

        f.pack();
        f.setVisible(true);
    }
}