I'm completely new to java and am trying to get some experience with programming java applets that can be opened from a browser. I was able to successfully open a simple "hello world" applet from a browser using the below javascript:
<script src="http://www.java.com/js/deployJava.js"></script>
<script>
var attributes = { code:'HelloWorld.class'} ;
var parameters = {codebase_lookup:'true'};
deployJava.runApplet(attributes, parameters, '1.6');
</script>And java class:
import javax.swing.JApplet;
import javax.swing.SwingUtilities;
import javax.swing.JLabel;
public class HelloWorld extends JApplet {
//Called when this applet is loaded into the browser.
public void init() {
//Execute a job on the event-dispatching thread; creating this applet's GUI.
try {
SwingUtilities.invokeAndWait(new Runnable() {
public void run() {
JLabel lbl = new JLabel("Hello World");
add(lbl);
}
});
} catch (Exception e) {
System.err.println("createGUI didn't complete successfully");
}
}
}This all worked fine. I tried another tutorial where I used the Swing designer in NetBeans to create a Celsius to Farenheit conversion GUI. I want to make this same GUI appear in an applet thats opened from a browser. To do that I tried instantiating it within an applet class. Both classes are embedded in a larger class so I assume that they have access to each other's methods (http://java.sun.com/docs/books/tutorial/java/javaOO/nested.html).
/*
* webApp.java
*
* Created on December 29, 2009, 1:25 PM
*/
//package learn;
/**
*
* @author jake
*/
import javax.swing.JApplet;
import javax.swing.SwingUtilities;
import javax.swing.JLabel;
public class webApp {
class applet extends JApplet {
//Called when this applet is loaded into the browser.
public void init() {
//Execute a job on the event-dispatching thread; creating this applet's GUI.
try {
SwingUtilities.invokeAndWait(new Runnable() {
public void run() {
new CelsiusConverterGUI().setVisible(true);
}
});
}
catch (Exception e) {
System.err.println("createGUI didn't complete successfully");
}
}
}
class CelsiusConverterGUI extends javax.swing.JFrame {
/** Creates new form CelsiusConverterGUI */
public CelsiusConverterGUI() {
initComponents();
}
/** This method is called from within the constructor to
* initialize the form.
* WARNING: Do NOT modify this code. The content of this method is
* always regenerated by the Form Editor.
*/
// <editor-fold defaultstate="collapsed" desc="Generated Code">//GEN-BEGIN:initComponents
private void initComponents() {
tempTextField = new javax.swing.JTextField();
celsiusLabel = new javax.swing.JLabel();
convertButton = new javax.swing.JButton();
fahrenheitLabel = new javax.swing.JLabel();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
setTitle("Celsius Converter");
tempTextField.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
tempTextFieldActionPerformed(evt);
}
});
celsiusLabel.setText("Celsius");
convertButton.setText("Convert");
convertButton.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
convertButtonActionPerformed(evt);
}
});
fahrenheitLabel.setText("Fahrenheit");
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(convertButton)
.addComponent(tempTextField, javax.swing.GroupLayout.PREFERRED_SIZE, 141, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(63, 63, 63)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(celsiusLabel)
.addComponent(fahrenheitLabel))
.addContainerGap(56, Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(tempTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(celsiusLabel))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(convertButton)
.addComponent(fahrenheitLabel))
.addContainerGap(21, Short.MAX_VALUE))
);
layout.linkSize(javax.swing.SwingConstants.VERTICAL, new java.awt.Component[] {convertButton, tempTextField});
pack();
}// </editor-fold>//GEN-END:initComponents
private void tempTextFieldActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_tempTextFieldActionPerformed
// TODO add your handling code here:
}//GEN-LAST:event_tempTextFieldActionPerformed
private void convertButtonActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_convertButtonActionPerformed
//Parse degrees Celsius as a double and convert to Fahrenheit.
int tempFahr = (int)((Double.parseDouble(tempTextField.getText())) * 1.8 + 32);
fahrenheitLabel.setText(tempFahr + " Fahrenheit");
}//GEN-LAST:event_convertButtonActionPerformed
/**
* @param args the command line arguments
*/
// Variables declaration - do not modify//GEN-BEGIN:variables
private javax.swing.JLabel celsiusLabel;
private javax.swing.JButton convertButton;
private javax.swing.JLabel fahrenheitLabel;
private javax.swing.JTextField tempTextField;
// End of variables declaration//GEN-END:variables
}
}I compile this without errors and then use the same javascript described above with "webApp.class" replacing "HelloWorld.class". When I open the html file with the javascript, the applet says theres an error. Heres the details:
Java Plug-in 1.6.0_16
Using JRE version 1.6.0_16-b01 Java HotSpot(TM) Client VM
User home directory = /home/jake
----------------------------------------------------
c: clear console window
f: finalize objects on finalization queue
g: garbage collect
h: display this help message
l: dump classloader list
m: print memory usage
o: trigger logging
q: hide console
r: reload policy configuration
s: dump system and deployment properties
t: dump thread list
v: dump thread stack
x: clear classloader cache
0-5: set trace level to <n>
----------------------------------------------------
java.lang.reflect.InvocationTargetException
at com.sun.deploy.util.DeployAWTUtil.invokeAndWait(DeployAWTUtil.java:116)
at sun.plugin2.applet.Plugin2Manager.runOnEDT(Plugin2Manager.java:3336)
at sun.plugin2.applet.Plugin2Manager.createApplet(Plugin2Manager.java:2905)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Plugin2Manager.java:1397)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.ClassCastException: webApp cannot be cast to java.applet.Applet
at sun.plugin2.applet.Plugin2Manager$12.run(Plugin2Manager.java:2895)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:199)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Exception: java.lang.reflect.InvocationTargetException
java.lang.NullPointerException
at sun.plugin2.applet.Plugin2Manager.findAppletJDKLevel(Plugin2Manager.java:2996)
at sun.plugin2.applet.Plugin2Manager.createApplet(Plugin2Manager.java:2947)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Plugin2Manager.java:1397)
at java.lang.Thread.run(Thread.java:619)
Exception: java.lang.NullPointerExceptionIf anyone has any idea what I'm doing wrong here or how I can fix this, a response would be greatly appreciated!!!