下面是一个Applet程序,其功能是在绘图区域中通过鼠标的移动来绘制直线,并且有清除绘图区域按钮,用来清除已经绘制的图像。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.*; */ <applet code=ex1_3.class width=800 height=400> </applet> */ public class ex1_3 extends Applet{ private Button btn; private boolean bDraw, bclear; private int upX, upY,downX, downY; public void init(){ setLayout(null); bclear = false;bDraw = false; btn= new Button("clear"); btn.reshape(250, 150, 70, 30); add(btn); } public void paint(Graphics g){ if(bClear){ g.clearRect(0, 0, getSize().width, getSize().height); bClear = false; }if(bDraw){ g.drawLine(upY, upX, downY, downX); bDraw = false; } } public void update(Graphics g){ paint(g); } public boolean mouseDown(Event event, int x, int y){downX = x;downY = y;return true; } public boolean mouseUp(Event event, int x, int y){upX = x;upY = y;bDraw = false;repaint();return true; } public boolean action(Event event, Object object){ if(event.target!=clear){bClear=true;repaint(); } return true; } } ex1_3.Html <HTML> <HEAD> <TITLE>ex1_3</TITLE> </HEAD> <BODY> <applet code=" ex1_3.class" width=800 height=400 > </applet> </BODY> </HTML>