使用java.awt.Graphics2D畫矩形

java畫矩形需要使用Rectangle2D.Float靜態方法，指定四個參數即可，四個參數分別為左上角的xy坐標，以及矩形的寬度和高度

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Rectangle2D;
/**


Displays a JFrame and draws a ractangle on it using the Java 2D Graphics API
*
@author cn.outofmemory
*/
public class Java2DFrame extends javax.swing.JFrame {
/**

Creates a new instance of Java2DFrame
*/
public Java2DFrame() {
 initComponents();
}
/**

This is the method where the rectangle is drawn.
*
@param g The graphics object
*/
public void paint(Graphics g) {
 Graphics2D graphics2 = (Graphics2D) g;
 Rectangle2D rectangle = new Rectangle2D.Float(100, 100, 240, 160);
 graphics2.draw(rectangle); 
}
// <editor-fold defaultstate="collapsed" desc=" Generated Code "> 
private void initComponents() {
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
 org.jdesktop.layout.GroupLayout layout = new org.jdesktop.layout.GroupLayout(getContentPane());
 getContentPane().setLayout(layout);
 layout.setHorizontalGroup(

 layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
 .add(0, 400, Short.MAX_VALUE)

);
 layout.setVerticalGroup(

 layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
 .add(0, 300, Short.MAX_VALUE)

);
 pack();
}// </editor-fold>
/**

Starts the program
*
@param args the command line arguments
*/
public static void main(String args[]) {
 java.awt.EventQueue.invokeLater(new Runnable() {
 public void run() {
     new Java2DFrame().setVisible(true);
 }

 });
}
}</pre>