注意额外的注释。
import java.awt.*;import java.awt.event.*;import javax.swing.*;import javax.swing.border.*;class JavaPaintUI extends Jframe { private int tool = 1; int currentX, currentY, oldX, oldY; public JavaPaintUI() { initComponents(); } private void initComponents() { // we want a custom Panel2, not a generic JPanel! jPanel2 = new Panel2(); jPanel2.setBackground(new java.awt.Color(255, 255, 255)); jPanel2.setBorder(BorderFactory.createBevelBorder(BevelBorder.RAISED)); jPanel2.addMouseListener(new MouseAdapter() { public void mousePressed(MouseEvent evt) { jPanel2MousePressed(evt); } public void mouseReleased(MouseEvent evt) { jPanel2MouseReleased(evt); } }); jPanel2.addMouseMotionListener(new MouseMotionAdapter() { public void mouseDragged(MouseEvent evt) { jPanel2MouseDragged(evt); } }); // add the component to the frame to see it! this.setContentPane(jPanel2); // be nice to testers.. this.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE); pack(); }// </editor-fold> private void jPanel2MouseDragged(MouseEvent evt) { if (tool == 1) { currentX = evt.getX(); currentY = evt.getY(); oldX = currentX; oldY = currentY; System.out.println(currentX + " " + currentY); System.out.println("PEN!!!!"); } } private void jPanel2MousePressed(MouseEvent evt) { oldX = evt.getX(); oldY = evt.getY(); System.out.println(oldX + " " + oldY); } //mouse released// private void jPanel2MouseReleased(MouseEvent evt) { if (tool == 2) { currentX = evt.getX(); currentY = evt.getY(); System.out.println("line!!!! from" + oldX + "to" + currentX); } } //set ui visible// public static void main(String args[]) { EventQueue.invokeLater(new Runnable() { public void run() { new JavaPaintUI().setVisible(true); } }); } // Variables declaration - do not modify private JPanel jPanel2; // End of variables declaration // This class name is very confusing, since it is also used as the // name of an attribute! //class jPanel2 extends JPanel { class Panel2 extends JPanel { Panel2() { // set a preferred size for the custom panel. setPreferredSize(new Dimension(420,420)); } @Override public void paintComponent(Graphics g) { super.paintComponent(g); g.drawString("BLAH", 20, 20); g.drawRect(200, 200, 200, 200); } }}
