一个画图程序paint问题

Question

恩，估计你是通过在JPanel上getGraphics来得到Graphics对象然后进行画图的吧
建议你扩展JPanel类，直接重写paint(Graphics g)方法就能够解决这个问题了

Answer 1

只是在JPanel绘图的,主类继承了jpanel。是直接重写paint函数的,paint函数如下:
public void paint(Graphics g){
    super.paint(g);
    Graphics2D g2D=(Graphics2D)g;
    g2D.setColor(Color.red);
    g2D.setStroke(new BasicStroke(1.2f));
    g2D.setFont(new Font("宋体",0,15));
    g2D.drawString("My draw program!",0,-10);
    for(int i=0;i<trace.size()-1;i++){
      g2D.drawLine((int)((Point2D.Double)trace.elementAt(i)).getX(),
                   -(int)((Point2D.Double)trace.elementAt(i)).getY(),
                   (int)((Point2D.Double)trace.elementAt(i+1)).getX(),
                   -(int)((Point2D.Double)trace.elementAt(i+1)).getY());
    }
    g2D.setStroke(new BasicStroke(1.0f));
    g2D.setColor(Color.blue);
    g2D.drawLine(0,0,30,-220);
  }

Answer 2

在适当的时候使用repaint重画，如何？

Answer 3

不知道这个帖子对你有没有帮助
http://expert.csdn.net/Expert/topic/1682/1682278.xml?temp=.8472864

Answer 4

你必须在弹对话框之后显示的调repaint()

Answer 5

你应该覆写paintComponent方法，而不是paint方法public void paintComponent(Graphics g){
    super.paintComponent(g);
    Graphics2D g2D=(Graphics2D)g;
    g2D.setColor(Color.red);
    g2D.setStroke(new BasicStroke(1.2f));
    g2D.setFont(new Font("宋体",0,15));
    g2D.drawString("My draw program!",0,-10);
    for(int i=0;i<trace.size()-1;i++){
      g2D.drawLine((int)((Point2D.Double)trace.elementAt(i)).getX(),
                   -(int)((Point2D.Double)trace.elementAt(i)).getY(),
                   (int)((Point2D.Double)trace.elementAt(i+1)).getX(),
                   -(int)((Point2D.Double)trace.elementAt(i+1)).getY());
    }
    g2D.setStroke(new BasicStroke(1.0f));
    g2D.setColor(Color.blue);
    g2D.drawLine(0,0,30,-220);
  }