10.5（简单的绘图程序）...

创建一个简单的绘图程序，可以绘制矩形，椭圆和直线。

1.先生成程序界面：

创一个添加显示图片按钮的方法：

1 privateJButton addButton(String str){2 ImageIcon icon = new ImageIcon(str);//按钮图标

3 JButton button = newJButton(icon);4 button.setContentAreaFilled(false);//按钮透明；

5 returnbutton;6 }

初始化界面：

1 public voidinit(){2 setLayout(new BorderLayout(5,1)); //设置布局；

3 JButton rectFilled = addButton("rectfilled.gif");4 rectFilled.setActionCommand("rectFilled");5 JButton rect = addButton("rect.gif");6 rect.setActionCommand("rect");7 JButton ovalFilled = addButton("ovalfilled.gif");8 ovalFilled.setActionCommand("ovalFilled");9 JButton oval = addButton("oval.gif");10 oval.setActionCommand("oval");11 JButton line = addButton("line.gif");12 line.setActionCommand("line");13 add(rectFilled, BorderLayout.WEST);14 add(rect, BorderLayout.WEST);15 add(ovalFilled, BorderLayout.WEST);16 add(oval, BorderLayout.WEST);17 add(line, BorderLayout.WEST);18 }

2.创建按钮事件

点击按钮分别执行的事件；为了点击按钮画出相应的图形，我设置了5个boolean变量；

private boolean isDrawRectFilled = false, isDrawRect = false, isDrawOvalFilled = false, isDrawOval = false, isDrawLine = false;

按钮事件代码：

1 public voidactionPerformed(ActionEvent e){2 String cmd =e.getActionCommand();3 if(cmd.equals("rectFilled")){4 isDrawRectFilled = true;5 isDrawRect = false;6 isDrawOval = false;7 isDrawOvalFilled = false;8 isDrawLine = false;9 } else if (cmd.equals("rect")){10 isDrawRect = true;11 isDrawRectFilled = false;12 isDrawOval = false;13 isDrawOvalFilled = false;14 isDrawLine = false;15 } else if (cmd.equals("ovalFilled")){16 isDrawRectFilled = false;17 isDrawRect = false;18 isDrawOval = false;19 isDrawOvalFilled = true;20 isDrawLine = false;21 } else if (cmd.equals("oval")){22 isDrawRectFilled = false;23 isDrawRect = false;24 isDrawOval = true;25 isDrawOvalFilled = false;26 isDrawLine = false;27 } else if (cmd.equals("line")){28 isDrawRectFilled = false;29 isDrawRect = false;30 isDrawOval = false;31 isDrawOvalFilled = false;32 isDrawLine = true;33 }34 }

分别将所需要画出的图形设为true，将其他设置为false；

3.主要的部分：鼠标点击和拖拽，画出相应的图形：

(1)先定义一个GPiont 变量用于储存鼠标按下的位置：

private GPoint press; //记录鼠标按下的点；

(2)分别创建储存相应图形的变量；

private GLine line;

private GRect rect;

private GOval oval;

(3)画矩形和画椭圆的代码类似；

分别设置他们的坐标和宽和高：

double x = press.getX();

double y = press.getY();

double width = e.getX() - press.getX();

double height = e.getY() - press.getY();

同时位置确保在每个方向都能画出图形，需要设置

//确保向左下方拖拽也能画出图形；

if(width < 0 ){

x = e.getX();

width = -width;

}

//确保向上方拖拽也能画出图形；

if(height < 0){

y = e.getY();

height = -height;

}

(4)画直线比较简单：

鼠标点击事件中加入一个：

line = new GLine(e.getX(), e.getY(),e.getX(), e.getY());

在鼠标拖拽事件中设置终点：

line.setEndPoint(e.getX(),e.getY());

4.同时要允许可以拖动画出的图形：

设置一个GObject 变量，储存鼠标按下点的图形，如果不是null则拖动当前图形不是绘画。

1 if(gobj != null){2 gobj.move(e.getX() - press.getX(), e.getY() -press.getY());3 press = newGPoint(e.getPoint());4 }

5.鼠标点击图形将其移动到最前

if(gobj != null){

gobj.sendToFront();

}

最后的效果：

完整代码：

1 import acm.graphics.*;2 import acm.program.*;3

4 import java.awt.*;5 import java.awt.event.*;6

7 import acm.gui.*;8 import javax.swing.*;9

10 public class SimpleDraw extendsGraphicsProgram {11 //初始化界面

12 public voidinit(){13 setLayout(new BorderLayout(5,1)); //设置布局；

14 JButton rectFilled = addButton("rectfilled.gif");15 rectFilled.setActionCommand("rectFilled");16 JButton rect = addButton("rect.gif");17 rect.setActionCommand("rect");18 JButton ovalFilled = addButton("ovalfilled.gif");19 ovalFilled.setActionCommand("ovalFilled");20 JButton oval = addButton("oval.gif");21 oval.setActionCommand("oval");22 JButton line = addButton("line.gif");23 line.setActionCommand("line");24 add(rectFilled, BorderLayout.WEST);25 add(rect, BorderLayout.WEST);26 add(ovalFilled, BorderLayout.WEST);27 add(oval, BorderLayout.WEST);28 add(line, BorderLayout.WEST);29 addActionListeners();30 addMouseListeners();31 }32 /*

33 * 添加按钮方法，str 是显示的图片的路径；34 */

35 privateJButton addButton(String str){36 ImageIcon icon = new ImageIcon(str);//按钮图标

37 JButton button = newJButton(icon);38 button.setContentAreaFilled(false);//按钮透明；

39 returnbutton;40 }41 /*侦听的按钮事件*/

42 public voidactionPerformed(ActionEvent e){43 String cmd =e.getActionCommand();44 if(cmd.equals("rectFilled")){45 isDrawRectFilled = true;46 isDrawRect = false;47 isDrawOval = false;48 isDrawOvalFilled = false;49 isDrawLine = false;50 } else if (cmd.equals("rect")){51 isDrawRect = true;52 isDrawRectFilled = false;53 isDrawOval = false;54 isDrawOvalFilled = false;55 isDrawLine = false;56 } else if (cmd.equals("ovalFilled")){57 isDrawRectFilled = false;58 isDrawRect = false;59 isDrawOval = false;60 isDrawOvalFilled = true;61 isDrawLine = false;62 } else if (cmd.equals("oval")){63 isDrawRectFilled = false;64 isDrawRect = false;65 isDrawOval = true;66 isDrawOvalFilled = false;67 isDrawLine = false;68 } else if (cmd.equals("line")){69 isDrawRectFilled = false;70 isDrawRect = false;71 isDrawOval = false;72 isDrawOvalFilled = false;73 isDrawLine = true;74 }75 }76 public voidmousePressed(MouseEvent e){77 press = newGPoint(e.getPoint());78 gobj =getElementAt(press);79 if(gobj != null){80 gobj.sendToFront();81 }82 line = newGLine(e.getX(), e.getY(),e.getX(), e.getY());83 rect = new GRect(0,0);84 oval = new GOval(0,0);85 }86 //鼠标拖拽事件

87 public voidmouseDragged(MouseEvent e){88 double x =press.getX();89 double y =press.getY();90 double width = e.getX() -press.getX();91 double height = e.getY() -press.getY();92 line.setEndPoint(e.getX(),e.getY());93 //确保向左下方拖拽也能画出图形；

94 if(width < 0){95 x =e.getX();96 width = -width;97 }98 //确保向上方拖拽也能画出图形；

99 if(height < 0){100 y =e.getY();101 height = -height;102 }103 rect.setSize(width, height);104 oval.setSize(width, height);105 if(gobj != null){106 gobj.move(e.getX() - press.getX(), e.getY() -press.getY());107 press = newGPoint(e.getPoint());108 } else{109 if(isDrawRectFilled == true){110 rect.setFilled(true);111 add(rect, x, y);112 }113 if(isDrawRect == true){114 add(rect, x, y);115 }116 if(isDrawOval == true){117 add(oval, x, y);118 }119 if(isDrawOvalFilled == true){120 oval.setFilled(true);121 add(oval, x, y);122 }123 if(isDrawLine == true){124 add(line);125 }126 }127 }128

129 private boolean isDrawRectFilled = false, isDrawRect = false, isDrawOvalFilled = false, isDrawOval = false, isDrawLine = false;130 privateGLine line;131 privateGRect rect;132 privateGOval oval;133 private GPoint press; //记录鼠标按下的点；

134 private GObject gobj; //记录鼠标按下点的图形；

135 }