Test1.java

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Class Test1 is an example of a simple Java program that provides the starting-point for demonstrating graphics applications. The class provides a JFrame application with a custom client window derived from JPanel.

In this example, the custom JPanel displays the width and height of the client area, centered in the screen. It illustrates the use of FontMetrics to obtain the graphical extent of a text string in Java.

This version initializes the user interface in the event dispatch thread. It used to be perfectly acceptable to carry out the intialization in the main thread. Sadly, as Swing components have gotten more complex, it is not possible to guarantee the safety of that approach. The probability of an error is extremely low, but at least you know how to do the right thing.

01: // Test1.java
02: import java.awt.EventQueue;
03: import java.awt.Graphics;
04: import java.awt.FontMetrics;
05: import java.awt.geom.Rectangle2D;
06: import javax.swing.JPanel;
07: import javax.swing.JFrame;
08: 
09: public class Test1 extends JPanel
10: {
11:     public void paintComponent(Graphics g)
12:     {
13:         super.paintComponent( g );
14:         int width = getWidth();
15:         int height = getHeight();
16:         String str = String.format("width %d height %d",width,height);
17:         FontMetrics fm = g.getFontMetrics();
18:         Rectangle2D rect = fm.getStringBounds(str,g);
19:         width -= rect.getWidth();
20:         height -= rect.getHeight();
21:         g.drawString(str,width/2,height/2);
22:     }
23: 
24:     public static void main( String args[] )
25:     {
26:         EventQueue.invokeLater(new Runnable()
27:         {
28:             public void run()
29:             {
30:                 Test1 panel = new Test1();
31:                 JFrame application = new JFrame("Test1");
32:                 application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
33:                 application.add(panel);
34:                 application.setSize(200,200);
35:                 application.setVisible(true);
36:             }
37:         });
38:     }
39: }

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Maintained by John Loomis, updated Wed Mar 12 10:37:27 2008