问答题

综合应用题 下面是一个Applet程序，实现实心或者空心矩形的绘制。要求鼠标在Applet窗口中拖动实现矩形的绘制，可以选择填充或者空心，有按钮用来清空窗口中的图像。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。 程序运行结果如下：
import java.awt.*; import java.applet.*; /* */ public class ex13_3 extends Applet{ private Button btnClear; private CheckboxGroup cbg; private Checkbox chk1, chk2; private int upX, upY; private int downX, downY; private boolean bDraw, bClear, bStyle; public void init(){ bDraw = false; bClear = false; bStyle = false; setLayout(null); cbg = new CheckboxGroup(); chk1 = new Checkbox("Hollow", cbg, true); chk2 = new Checkbox("Filled", cbg, false); chk1.reshape(80,getSize().height-80,80,25); chk2.reshape(160,getSize().height-80,80,25); add(chk1); add(chk2); btnClear = new Button("clear"); btnClear.reshape(240,getSize().height-80,80,25); add(btnClear); } public void paint(Graphics g){ if(bDraw){ if(upX > downX && upY > downY){ if(bStyle) g.fillRect(downX, downY, upX - downX, upY - downY); else g.drawRect(downX, downY, upX - downX, upY - downY); } else if(upX > downX && upY < downY){ if(bStyle) g.fillRect(downX, upY, upX - downX, downY - upY); else g.drawRect(downX, upY, upX - downX, downY - upY); } else if(upX < downX && upY > downY){ if(bStyle) g.fillRect(upX, downY, downX - upX, upY - downY); else g.drawRect(upX, downY, downX - upX, upY - downY); } else if(upX < downX && upY < downY){ if(bStyle) g.fillRect(upX, upY, downX - upX, downY - upY); else g.drawRect(upX, upY, downX - upX, downY - upY); } bDraw = false; } if(bClear){ g.clearRect(0,0, getSize().height, getSize().width); bClear = false; } } public void update(Graphics g){ paint(g); } public boolean mouseUp(Event e, int x, int y){ upX = x; upY = y; bDraw = true; repaint(); return true; } public boolean mouseDown(Event e, int x, int y){ downX = x; downY = y; return true; } public boolean action(Event e, Object o){ if(e.target == btnClear){ bClear = true; repaint(); } if(chk1.getState() == true){ bStyle = true; } if(chk2.getState() == true){ bStyle = false; } return true; } } ex13_3.html