JApplet : Java Glossary

JApplet

Allows java programs to run in browsers. It is the swing version of Applet and it behaves the same.

Switch Hitter

By adding the following method to your Applet, you can allow it be run either as an Applet or as an application. If your Applet were called MyApplet, here is the code to add to the MyApplet class to make it also into an application:

Your Applet can get hold of the parameters in the HTML (Hypertext Markup Language).
That code is quite crude. It will not do such things as:

Simulate the getParameter method to get at the JApplet parameters.
Adjust the coordinate system so part of the JApplet is not hidden under the JFrame menu bar. Layout managers deal with this automtically, but if you do absolute positioning, you have to compensate manually.

The easiest way to deal with these problems is to use two JApplet constructors, one the usual default constructor and one that passes the param information in. Inside you can keep track of which mode you are running in with a boolean you set in the constructor. getParameter( favouriteColour ) will return the String orange. When you write an Applet often you will override some of the following methods: init(), start(), stop(), destroy() and paint(Graphics g). There is equivalent code for Applet.

Converting an Applet to a JApplet

Here is how I convert an Applet to a JApplet.

Change extends Applet to extends JApplet.
Change component types from Button to JButton, Label to JLabel (Label. LEFT to JLabel. LEFT etc.), TextField to JTextField, TextArea to JTextArea, Frame to JFrame. You won’t get compiler errors if you erroreously leave some old AWT (Advanced Windowing Toolkit) components in there.
Convert Choice to JComboxBox. Rename the Choice. select method to JComboxBox. setSelectedItem or JComboxBox.setSelectedIndex. You can often simplify the logic by feeding the JComboBox composite objects for the choices with a toString method for the string to display.
Insert Container contentPane = getContentPane(); then use contentPane. setLayout, contentPane. setBackground and contentPane.add instead of using the JApplet methods. You won’t get compile-time error messages if you fail to do this. If you screw up, your code may work under Java version 1.6 but not older JDKs (Java Development Kits).
For numeric fields, consider using a JSpinner.

Learning More

Oracle’s Javadoc on JApplet class : available:

on the web at Oracle.com
in the current JDK 1.7.0_17 or in the old JDK 1.6.0_45 on your local Windows J: drive.

Oracle’s tutorial on Applet

Gotchas

JApplet is not a JComponent. Its ancestry is Applet, Panel, Container, Component. This means it has no paintComponent method for example.

Applet
AWT
browsershots
Choice
copy/paste
JavaScript
JButton
JComboBox
JFrame
JLabel
JSpinner
JTextArea
JTextField
pane
Swing
window differences

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