2.7怎样将这些面向对象的概念转换为代码
2.7.1ClickMe的源代码和Applet标签
为了编译这个applet你需要两个源文件:ClickMe.java和Spot.java。为了运行这个applet你需要利用这个applet标签来创建一个html文件:
<applet code="ClickMe.class" width="300px" height="150px"></applet> 其中ClickMe.java的源代码为: import java.applet.Applet; import java.awt.*; import java.awt.event.*; public class ClickMe extends Applet implements MouseListener { private Spot spot = null; private static final int RADIUS = 7; public void init() { addMouseListener(this); } public void paint(Graphics g) { //画一个黑边框和白背景 g.setColor(Color.white); g.fillRect(0, 0, getSize().width - 1, getSize().height - 1); g.setColor(Color.black); g.drawRect(0, 0, getSize().width - 1, getSize().height - 1); //画红点 g.setColor(Color.red); if (spot != null) { g.fillOval(spot.x - RADIUS, spot.y - RADIUS, RADIUS * 2, RADIUS * 2); } } public void mousePressed(MouseEvent event) { if (spot == null) { spot = new Spot(RADIUS); } spot.x = event.getX(); spot.y = event.getY(); repaint(); } public void mouseClicked(MouseEvent event) {} public void mouseReleased(MouseEvent event) {} public void mouseEntered(MouseEvent event) {} public void mouseExited(MouseEvent event) {} } 而Spot.java的源代码为: public class Spot { public int size; public int x, y; public Spot(int intSize) { size = intSize; x = -1; y = -1; } }
然后装载网页到浏览器或者appletviewer工具。并且确保所有必要的文件都在相同的目录中。 如图11所示:
(图11)
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