问答题

下面是一个Applet程序,其功能是将完整的图像显示于Applet的区块中,然后可以通过拖动鼠标让图像随着鼠标拖动的轨迹而移动。请改正程序中的错误(有下划线的语句),使程序能输出正确的结果。注意:不改动程序的结构,不得增行或删行。 源程序文件代码清单如下: import java.applet.*; import java.awt.*; /* <applet code="ex7_3.class" width=800 height=400 > </applet> */ public class ex7_3 extends Applet { private Image iImg; private int xPos,yPos; public void init() { xPos = yPos = 0; iImg = getImage("ex7_3.jpg"); } public void paint(Graphics g) { g.drawImage(iImg,xPos,yPos); } public boolean mouseDrag(Event e,int x, int y) { xPos = x; yPos = y; paint(); return true; } } ex7_3.html <HTML> <HEAD> <TITLE>ex7_3</TITLE> </HEAD> <BODY> <applet code="ex7_3.class" width=800 height=400 > </applet> </BODY> </HTML>

【参考答案】

iImg=getImage(getDocumentBase(),"ex7_3.jpg") g.drawImaSe(iIm......

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以下程序中,当用户单击“移动”按钮以后,就可以使用方向键控制屏幕上句子的移动,单击“停止”按钮,则句子不再随着方向键移动。运行结果如下图所示注意:请勿改动其他已有语句内容,仅在横线处填入适当语句。import java.applet.*;import java.awt.*;import java.awt.event.*;public class Example2_8 extends Applet implements KeyListener{public void keyTyped(KeyEvent e) {}public void keyReleased(KeyEvent e) {}Button button;Button stopButton;Label out;int x,y;public void _______ (){button = new Button( 移动 );button.addActionListener(new AddMoveListener(this));stopButton = new Button( 停止移动 );stopButton.addActionListener(new RemoveListener(this));stopButton.setEnabled(false);out = new nabel( 按下按钮以后我可以随方向键移动 );add(button);add(stopButton);add (out);}public void start(){super, start ();}public void keyPressed(KeyEvent e){x=out.getBounds().x;y=out.getBounds().y;if(e.getKeyCode()==KeyEvent.VK_UP){y=y-2;if(y<=0) y=0;out. setLocation (x, y);} else if(e.getKeyCode()==KeyEvent.VK_DOWN){ y=y+2;if (y>=300) y=300;out. setLocation (x, y);}else if(e.getKeyCode()==KeyEvent.VK_LEFT){x=x-2;if(x<=0) x=0;out. setLocation (x, y);}else if(e.getKeyCode()==KeyEvent.VK_RiGHT){x=x+2;if(x>=300) x=300;out. setLocation (x, y);}}class AddMoveListener implements ActionListener{Example2_8 lis;public AddMoveListener(Example2_8 lis){this.lis = lis;}public void actionPerformed(ActionEvent e){button. _________(lis);stopButton, setEnabled (true);}}class RemoveListener implements ActionListener{Example2_8 lis;public RemoveListener(Example2_8 lis){this.lis = lis;}public void actionPerformed(ActionEvent e){button, removeKeyListener (lis);stopButton.setEnabled(false);}}}Example2_8. html<HTML><HEAD><TITLE> Example2_8< TITLE>< HEAD><BODY><APPLET CODE= Example2_8.class WIDTH=400 HEIGHT=500>< APPLET>< BODY>< HTML>