- An applet is a
derived class
of
Panel
(See:
click here
- A Panel is similar to
JPanel:
- Use the add(..) method
to add/stick graphical components
on an applet
- Do NOT
use:
getContentPane.add(...)because there is no contentPane in an applet (a contentPane is part of a Frame)
- Use the add(..) method
to add/stick graphical components
on an applet
- An applet does
NOT have a
constructor:
-
The applet's init() method
is invoked by
the web browser
when an applet is loaded
- GUI application -> Applet conversion Algorithm:
- Delete the
class that contains
the main function
-
This class is used to invoke the
constructor
of the
derived JFrame class.
This class is no longer necessary, since the browser invokes the void init() method
Example:
public class CopyText2 { public static void main(String[] args) { TextFrame frame = new TextFrame(500, 500); frame.setTitle("TextTest"); frame.setVisible(true); } }
- Import the class
Applet
Make the GUI class public
And make the GUI class extend Applet
Example:
import java.applet.Applet; public class CopyText2 extends Applet
- Rename
the constructor of the
GUI class
to
void init()
Delete any super(...) call (init() is not a constructor)
Delete any setSize(...) calls (the applet has been given a size by the browser)
Example:
public class TextFrame extends Applet <-------- !!! {TextFrame(int width, int height)void init() {super(Title); setSize(width, height);// Set frame size .... .... } }
- Change
all calls to:
getContentPane.add(...);
into:
add(...);
Example:
public class TextFrame extends Applet { void init() { .... ....contentPane.add(buttonPanel, "South");add(buttonPanel, "South"); } }
- Delete the
class that contains
the main function
- Graphical Application:
import java.awt.*; import java.awt.event.*; import javax.swing.*; import java.util.StringTokenizer; public class TextTest { public static void main(String[] args) { TextFrame frame = new TextFrame("TextTest"); frame.setVisible(true); } } class TextFrame extends JFrame { private JTextArea inputArea; // Text area for input private JTextField resultField; // Text area for output private JButton calcButton; // Button to trigger calculation public TextFrame(String Title) { super(Title); setSize(500, 500); // Set frame size inputArea = new JTextArea(); // Default is editable... resultField = new JTextField(20); resultField.setEditable(false); // No editing allowed here.... calcButton = new JButton("Calculate"); getContentPane().setLayout( new BorderLayout() ); getContentPane().add(inputArea, "Center"); JPanel resultPanel = new JPanel(); // JPanel for sexy effect resultPanel.add(new JLabel("Average: ")); // Add label first resultPanel.add(resultField); // Then add output text area JPanel buttonPanel = new JPanel(); // Make a panel buttonPanel.add(calcButton); // Add Calculate button JPanel southPanel = new JPanel(); // Make a panel southPanel.setLayout(new GridLayout(2, 1)); // We need a Grid layout... southPanel.add(resultPanel); // Add first panel southPanel.add(buttonPanel); // Stack second panel getContentPane().add(southPanel, "South"); calcButton.addActionListener(new ButtonListener()); // Press to calculate! } /* ============================================================= Listener class for the Calculate button ============================================================= */ private class ButtonListener implements ActionListener { public void actionPerformed(ActionEvent event) { String input; double sum; int i, N; // get user input from text area input = inputArea.getText(); // Get input // Tokenize the string StringTokenizer tokenizer = new StringTokenizer(input); N = tokenizer.countTokens(); sum = 0; for ( i = 0; i < N; i++ ) sum += Double.parseDouble(tokenizer.nextToken()); // display in result field resultField.setText("" + sum/N); } } }
- Applet:
import java.awt.*; import java.awt.event.*; import javax.swing.*; import java.util.StringTokenizer; import java.applet.Applet; <-------- !!! // public class TextTest // { public static void main(String[] args) // { // TextFrame frame = new TextFrame("TextTest"); // frame.setVisible(true); // } // } // class TextFrame extends JFrame class TextFrame extends Applet <-------- !!! { private JTextArea inputArea; // Text area for input private JTextField resultField; // Text area for output private JButton calcButton; // Button to trigger calculation public TextFrame(String Title) { // super(Title); // setSize(500, 500); // Set frame size inputArea = new JTextArea(); // Default is editable... resultField = new JTextField(20); resultField.setEditable(false); // No editing allowed here.... calcButton = new JButton("Calculate");getContentPane().setLayout( new BorderLayout() );getContentPane().add(inputArea, "Center"); JPanel resultPanel = new JPanel(); // JPanel for sexy effect resultPanel.add(new JLabel("Average: ")); // Add label first resultPanel.add(resultField); // Then add output text area JPanel buttonPanel = new JPanel(); // Make a panel buttonPanel.add(calcButton); // Add Calculate button JPanel southPanel = new JPanel(); // Make a panel southPanel.setLayout(new GridLayout(2, 1)); // We need a Grid layout... southPanel.add(resultPanel); // Add first panel southPanel.add(buttonPanel); // Stack second panelgetContentPane().add(southPanel, "South"); calcButton.addActionListener(new ButtonListener()); // Press to calculate! } /* ============================================================= Listener class for the Calculate button ============================================================= */ private class ButtonListener implements ActionListener { public void actionPerformed(ActionEvent event) { String input; double sum; int i, N; // get user input from text area input = inputArea.getText(); // Get input // Tokenize the string StringTokenizer tokenizer = new StringTokenizer(input); N = tokenizer.countTokens(); sum = 0; for ( i = 0; i < N; i++ ) sum += Double.parseDouble(tokenizer.nextToken()); // display in result field resultField.setText("" + sum/N); } } }
- Example Program:
(Demo above code)
- Applet Prog file: click here
- The original Grpahical Application Prog file is here: click here
How to run an applet:
1. Compile: javac TextFrame.java 2. Make a webpage that loads the applet (see below) 3a. Testing: use appletviewer webpage 3b. For real: point browser to the webpage
- Pre-requisite:
- You need to get a copy of the Java plugin classes12.zip in the directory where your applet is found
A copy of the Java plugin classes12.zip can be found here: RIGHT click and save
- The
EMBED
tag is used to
load
applets
Example:
<EMBED type="application/x-java-applet;version=1.2" archive="classes12.zip" code="TextFrame.class" WIDTH=400 HEIGHT=400> </EMBED>
- Here is a webpage to load the applet:
click here
Click on the link to load applet in browser
Load the webpage with appletviewer:
1. Save webpage 2. Save applet code 3. Compile applet code 4. Run: appletviewer Load-TextFrame.html