appletbutton.java

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/*
 * Swing version.
 * XXX: This should probably use a SwingWorker instead of a custom thread.
 */

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

public class AppletButton extends JApplet
                          implements Runnable, 
                                     ActionListener {
    int frameNumber = 1;
    String windowClass;
    String buttonText;
    String windowTitle;
    int requestedWidth = 0;
    int requestedHeight = 0;
    JButton button;
    Thread windowThread;
    JLabel label;
    boolean pleaseShow = false;
    boolean shouldInitialize = true;
    Class windowClassObject;

    public void init() {
        //Look up the parameters we need right away.
        windowClass = getParameter("WINDOWCLASS");
        if (windowClass == null) {
            windowClass = "TestWindow";
        }
        buttonText = getParameter("BUTTONTEXT");
        if (buttonText == null) {
            buttonText = "Click here to bring up a " + windowClass;
        }

        //Set up the button and label this applet displays.
        button = new JButton(buttonText);
        button.addActionListener(this);
        label = new JLabel("", JLabel.CENTER);

        //Add the button and label to this applet.
        Container contentPane = getContentPane();
        contentPane.setLayout(new GridLayout(2,0));
        contentPane.add(button);
        contentPane.add(label);
    }

    public void start() {
        if (windowThread == null) {
            windowThread = new Thread(this, "Bringing Up " + windowClass);
            windowThread.start();
        }
    }

    public void stop() {
        windowThread = null;
    }

    public synchronized void run() {
        Object object = null;
        JFrame window = null;
        String name = null;
        
        if (shouldInitialize) {
            //Look up the rest of the parameters.
            windowTitle = getParameter("WINDOWTITLE");
            if (windowTitle == null) {
                windowTitle = windowClass;
            }
            String windowWidthString = getParameter("WINDOWWIDTH");
            if (windowWidthString != null) {
                try {
                    requestedWidth = Integer.parseInt(windowWidthString);
                } catch (NumberFormatException e) {
                    //Use default width.
                }
            }
            String windowHeightString = getParameter("WINDOWHEIGHT");
            if (windowHeightString != null) {
                try {
                    requestedHeight = Integer.parseInt(windowHeightString);
                } catch (NumberFormatException e) {
                    //Use default height.
                }
            }
 
            //Make sure the window class exists.
            try {
                windowClassObject = Class.forName(windowClass);
            } catch (Exception e) {
                //The specified class isn't anywhere that we can find.
                label.setText("Bad parameter: Couldn't find class "
                              + windowClass);
                button.setEnabled(false);
                return;
            }
    
            //Create an invisible instance.
            window = createWindow(windowTitle);
            if (window == null) {
                return;
            }

            shouldInitialize = false;
        }

        Thread currentThread = Thread.currentThread();
        while (currentThread == windowThread) {

            //Wait until we're asked to show a window.
            while (pleaseShow == false) {
                try {
                    wait();
                } catch (InterruptedException e) {
                }
            }

            //We've been asked to bring up a window.
            pleaseShow = false;

            //Create another window if necessary.
            if (window == null) { 
                window = createWindow(windowTitle + ": " 
                                      + ++frameNumber);
            } 

            window.setVisible(true);
            label.setText("");
            window = null;
        } //end thread loop
    }

    private JFrame createWindow(String title) {
        Object object = null;
        JFrame window = null;

        //Instantiate the window class.
        try {
            object = windowClassObject.newInstance(); 
        } catch (Exception e) {
            label.setText("Bad parameter: Can't instantiate "
                          + windowClassObject);
            button.setEnabled(false);
            return null;
        }

        //Make sure it's a frame.
        try {
            window = (JFrame)object;
        } catch (Exception e) {
            label.setText("Bad parameter: "
                          + windowClassObject +
                          " isn't a JFrame subclass.");
            button.setEnabled(false);
            return null;
        }

        window.setTitle(title);

        //Set its size.
        window.pack();
        if ((requestedWidth > 0) 
          | (requestedHeight > 0)) {
            window.setSize(Math.max(requestedWidth,
                                    window.getSize().width),
                           Math.max(requestedHeight,
                                    window.getSize().height));
        }

        return window;
    }
                
    /* Signal the window thread to build a window. */
    public synchronized void actionPerformed(ActionEvent event) {
        label.setText("Please wait while the window comes up...");
        pleaseShow = true;
        notify();
    }
}

class TestWindow extends JFrame {
    public TestWindow() {
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    }
}