drawRect()的小问题！

Question

startPoint.x=endPoint.x-startPoint.x；
endPoint.y-startPoint.y=startPoint.y

Answer 1

沒有問題吧
是不是因為有endPoint.x<startPoint.x這樣的情況

Answer 2

首先：调试程序是否运行到该case里
其次：看看两个点的坐标有没有问题

Answer 3

全部程序在这里了！
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import java.applet.*;
import java.awt.*;
import java.awt.event.*;
public class MyApplet extends Applet implements MouseListener,MouseMotionListener,ActionListener{ private Point startPoint,endPoint;
 private final int line=1;
 private final int rectangle=2;
 private final int circle=3; private int shape=0;
 private boolean blClear=false; private CheckboxGroup groupTypes,groupColors,groupFill;
 private Checkbox typeLine,typeRectangle,typeCircle;
 private Checkbox colorRed,colorGreen,colorBlue,colorPink,colorYellow;
 private Checkbox fill,notfill; private Button btnClear; public MyApplet()
{
 super();
}
 public void init(){
  addMouseListener(this);
  addMouseMotionListener(this);  btnClear=new Button("Clear");  groupTypes=new CheckboxGroup();
  groupColors=new CheckboxGroup();
  groupFill=new CheckboxGroup();  typeLine=new Checkbox("Line");
  typeRectangle=new Checkbox("Recangle");
  typeCircle=new Checkbox("Circle");
  typeLine.setCheckboxGroup(groupTypes);
  typeRectangle.setCheckboxGroup(groupTypes);
  typeCircle.setCheckboxGroup(groupTypes);  colorRed=new Checkbox("Red");
  colorGreen=new Checkbox("Green");
  colorBlue=new Checkbox("Blue");
  colorPink=new Checkbox("Pink");
  colorYellow=new Checkbox("Yellow");
  colorRed.setCheckboxGroup(groupColors);
  colorGreen.setCheckboxGroup(groupColors);
  colorBlue.setCheckboxGroup(groupColors);
  colorPink.setCheckboxGroup(groupColors);
  colorYellow.setCheckboxGroup(groupColors);  fill=new Checkbox("Fill");
  notfill=new Checkbox("Not fill");
  fill.setCheckboxGroup(groupFill);
  notfill.setCheckboxGroup(groupFill);  groupTypes.setSelectedCheckbox(typeLine);
  groupTypes.setSelectedCheckbox(colorBlue);
  groupTypes.setSelectedCheckbox(notfill);  typeLine.addMouseListener(this);
  typeRectangle.addMouseListener(this);
  typeCircle.addMouseListener(this);
  btnClear.addActionListener(this);
  colorRed.addMouseListener(this);
  colorGreen.addMouseListener(this);
  colorPink.addMouseListener(this);
  colorYellow.addMouseListener(this);
  fill.addMouseListener(this);  add(typeLine);
  add(typeRectangle);
  add(typeCircle);
  add(btnClear);
  add(fill);
  add(notfill);
  add(colorRed);
  add(colorGreen);
  add(colorBlue);
  add(colorPink);
  add(colorYellow);
 }
  public void paint(Graphics g){
  g.setColor(getCurrentColor());
  int currentType=getCurrentType();
  if(startPoint!=null && endPoint!=null && blClear==false){
   switch(currentType){
     case line:
      g.drawLine(startPoint.x,startPoint.y,endPoint.x,endPoint.y) ;
      break;
     case rectangle:
      checkPoints();
      if (!getFillStatus()){
        g.drawRect(startPoint.x,startPoint.y,endPoint.x-startPoint.x,endPoint.y-startPoint.y);
       }
       else{
        g.fillRect(startPoint.x,startPoint.y,endPoint.x-startPoint.x,endPoint.y-startPoint.y);
      }
       break;
      case circle:
       checkPoints();
       if(!getFillStatus()){
         g.drawArc(startPoint.x,startPoint.y,endPoint.x-startPoint.x,endPoint.y-startPoint.y,0,360);
           }
        else{
          g.fillArc(startPoint.x,startPoint.y,endPoint.x-startPoint.x,endPoint.y-startPoint.y,0,360);
       }
         break;
       }
 }
   blClear=false;
 }
  private void checkPoints(){
   Point temp;
   if(startPoint.x>endPoint.x){
     temp=startPoint;
     startPoint=endPoint;
     endPoint=temp;
     temp=null;
   }
 }private Color getCurrentColor(){
 Color currentColor=Color.blue;
 Checkbox selectedColor=groupColors.getSelectedCheckbox();
 if(selectedColor!=null){
   String lblColor=selectedColor.getLabel();
   if(lblColor.equals("Red")){
     currentColor=Color.red;
   }
   else if(lblColor.equals("Green")){
     currentColor=Color.green;
   }
   else if(lblColor.equals("Blue")){
     currentColor=Color.blue;
   }
   else if(lblColor.equals("Pink")){
     currentColor=Color.pink;
   }
   else if(lblColor.equals("Yellow")){
     currentColor=Color.yellow;
  }
 }
  return currentColor;
  }  public boolean getFillStatus(){
    boolean blFill=false;
    Checkbox selectedFill=groupFill.getSelectedCheckbox();
    if(selectedFill!=null){
     String lblColor=selectedFill.getLabel();
     if(lblColor.equals("Fill")){
      blFill=true;
     }
    }
    return blFill;
  }  private int getCurrentType(){
  int currentType=line;
  Checkbox selectedType=groupTypes.getSelectedCheckbox();
  if(selectedType!=null){
    String lblType=selectedType.getLabel();
    if(lblType.equals("Line")){
     currentType=line;
   }
    else if(lblType.equals("Circle")){
     currentType=circle;
    }
    else{
     currentType=line;
    }
  }
    return currentType;
  }
  public void mousePressed(MouseEvent e){
   startPoint=e.getPoint();
  }  public void mouseReleased(MouseEvent e){
   endPoint=e.getPoint();
   paint(this.getGraphics());
  }  public void mouseClicked(MouseEvent e){
  }  public void mouseDragged(MouseEvent e){
  }  public void mouseMoved(MouseEvent e)  {
  }  public void mouseEntered(MouseEvent e){
  }  public void mouseExited(MouseEvent e){
  }  public void actionPerformed(ActionEvent e){
   blClear=true;
   repaint();
  }
}

Answer 4

if(lblType.equals("Line")){
     currentType=line;
   }
    else if(lblType.equals("Circle")){
     currentType=circle;
    }
    else{
     currentType=line;
    }
  }
    return currentType;
  }
這一段里,你並沒有返回rectangle
是不是   else{
     currentType=line;
    }
要改為
   else{
     currentType=rectangle;
    }