app18.java

本程序实现了在一个窗口内用鼠标键拖曳自由绘图

//app18,拖曳鼠标绘图
import java.awt.*;
import java.awt.event.*;

public class app18 extends Frame implements MouseMotionListener,MouseListener
{
    static app18 frm=new app18();
    int x1,x2,y1,y2;
   public static void main(String arg[])
  {  
    frm.setTitle("Free drawing");
    frm.setSize(200,150);
    frm.addMouseListener(frm);//设置MouseListener
    frm.addMouseMotionListener(frm);//设置MouseMotionListener
    frm.setVisible(true);
  }
   public void mousePressed(MouseEvent e)
  {
    x1=e.getX();//取得按下鼠标时的X坐标（绘图起始点的X坐标）
    y1=e.getY();//取得按下鼠标时的Y坐标（绘图起始点的Y坐标）
  }
   public void mouseDragged(MouseEvent e)
  { 
   Graphics g=getGraphics();
   x2=e.getX();//取得拖曳鼠标时的X坐标
   y2=e.getY();//取得拖曳鼠标时的Y坐标
   paint(g);
  }
   public void paint(Graphics g)
  {
   g.drawLine(x1,y1,x2,y2);//绘出(x1,y1)到(x2,y2)的联机
   x1=x2;//更新绘图起始点的x坐标
   y1=y2;//更新绘图起始点的y坐标
  }
public void mouseMoved(MouseEvent e){}
public void mouseReleased(MouseEvent e) {}  
public void mouseEntered(MouseEvent e){}
public void mouseExited(MouseEvent e){}
public void mouseClicked(MouseEvent e){}

}