hellojava2.java

learning java的源代码。书中每个实例都有相关的代码example。

//file: HelloJava2.java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class HelloJava2
    extends JComponent implements MouseMotionListener {

  // Coordinates for the message
  int messageX = 125, messageY = 95;
  String theMessage;

  public HelloJava2(String message) {
    theMessage = message;
    addMouseMotionListener(this);
  }

  public void paintComponent(Graphics g) {
    g.drawString(theMessage, messageX, messageY);
  }

  public void mouseDragged(MouseEvent e) {
    // Save the mouse coordinates and paint the message.
    messageX = e.getX(  );
    messageY = e.getY(  );
    repaint(  );
  }

  public void mouseMoved(MouseEvent e) {}

  public static void main(String[] args) {
    JFrame f = new JFrame("HelloJava2");
    // Make the application exit when the window is closed.
    f.addWindowListener(new WindowAdapter(  ) {
      public void windowClosing(WindowEvent we) { System.exit(0); }
    });
    f.setSize(300, 300);
    f.getContentPane(  ).add(new HelloJava2("Hello, Java!"));
    f.setVisible(true);
  }
}