Question

java 在已有图形上用鼠标画图

如何不让界面在 鼠标第一次点击时自动刷新 以至于第一次点击所画的的图形被清掉！
原题：使用画直线，我已部分实现，关键是图形处理！
代码太长，发不了，完整代码找我
代码：
//Units.unit是一固定值！
public class selfpanel extends JPanel{
private int x1,y1,x2,y2;
public int Xaa,Xbb,Yaa,Ybb;
private JLabel status;
private JPanel p1 ;
private JPanel p2 ;
private JPanel p3 ;
private JButton clearpane;
private JTextArea JTextArea1;
Color color;
private int mark;
public selfpanel()
{
color=Color.blue;
x1=50;y1=50;x2=300;y2=300;
mark=1;

p1 = new JPanel();
p2 = new JPanel();
p3 = new JPanel();
status = new JLabel();
clearpane = new JButton("clear");
JTextArea1 = new JTextArea(10,15);

p1.setLayout(new FlowLayout());
p2.setLayout(new FlowLayout(FlowLayout.LEFT ));
p2.add(status);
p3.setLayout(new BorderLayout());
p3.add(clearpane,BorderLayout.NORTH);
p3.add(JTextArea1,BorderLayout.CENTER);

this.setLayout(new BorderLayout());
this.add(p1, BorderLayout.NORTH);
this.add(p2, BorderLayout.SOUTH);
this.add(p3, BorderLayout.EAST);

addMouseMotionListener(
new MouseMotionAdapter()
{
public void mouseMoved(MouseEvent event)
{
int i=event.getX()/Units.unit-1;
int j=event.getY()/Units.unit-1;
if(event.getX()<25||event.getY()<25||event.getX()>300||event.getY()>300)
{ i=0;j=0;}
status.setText(" "+ i + "," + j );
}
}
);

addMouseListener(
new MouseAdapter()
{
public void mousePressed(MouseEvent event)
{

if(event.getX()>=50&&event.getY()>=50&&event.getX()<=300&&event.getY()<=300&&mark<4)
{
drawfangkuai(event.getX(),event.getY());
mark = mark +1;
if(mark==3)
{
Xaa = event.getX(); Yaa = event.getY();
}
if(mark==4)
{
Xbb = event.getX(); Ybb = event.getY();
drawpoint();
mark = 2;
}
}

}
}
);

public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
g2.setColor(color);
drawLine(g2,x1,y1,x2,y2);

}
void drawLine(Graphics2D g,int x11,int y11,int x22,int y22)
{//画10*10网格 }
public void repaint()
{
Graphics g = getGraphics();
paint(g);
mark = 2;
}

public void drawpoint()
{
//根据Bresenham算法找到坐标，调用drawfangkuai画方块
}
void drawfangkuai(int startX,int startY)
{
//根据坐标画方块
}
出新问题了，每次触发点击鼠标事件后整个面板会刷新，这样，就不能在网格上连续画几条直线了。
问题：怎样让刷新不把以前画的图形清掉？（区域小方格的刷新，我已经知道了，有没有更高级的点的方法？）

Answer 1

这段代码给你参考下，实现功能：不让界面在 鼠标第一次点击时自动刷新 以至于第一次点击所画的的图形被清掉！至于画直线的，就需要你自己修改下代码，这个不难。

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;

public class freedraw1 extends Applet implements MouseMotionListener
{
int x,y;
public void init()
{
setBackground(Color.cyan);
setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));
addMouseMotionListener(this);
}

public void paint(Graphics g)
{
Graphics2D g2d=(Graphics2D)g;
g2d.setColor(Color.red);
BasicStroke bs1=new BasicStroke(4);
g2d.setStroke(bs1);
Line2D obj1=new Line2D.Double(x,y,x,y);
g2d.draw(obj1);
}

public void mouseDragged(MouseEvent e)
{
x=(int)e.getX();
y=(int)e.getY();
repaint();
}

public void update(Graphics g)
{
paint(g);
}

public void mouseMoved(MouseEvent e)
{
}

}