import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;
import java.awt.event.*;

public class Dda extends JFrame //主类

{
   JButton refresh=new JButton("refresh");

    PanelControl panelControl;
    Draw draws;

   public Dda( )
  {
     super("DDA");
    setSize(400,350);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JPanel pane = new JPanel();
    BorderLayout grid = new BorderLayout();
    pane.setLayout(grid);
    String[] coordinate={"x0","y0","x1","y1"};
    panelControl = new PanelControl(this,coordinate);
    draws = new Draw();

    pane.add(panelControl,"North");
    ane.add(draws,"Center");
    setContentPane(pane);

    setVisible(true);
   }
    public static void main(String[] arguments)
    {
     Dda frame=new Dda();
     }
//

   public static int x0,y0,x1,y1;
   void draw (PanelControl control)//传入的参数
   { 
      int[] value = new int[4];
      for (int i=0;i<4;i++)
      value[i] = Integer.parseInt(control.setting[i].getText());
      x0=value[0];y0=value[1];x1=value[2];y1=value[3];
      draws.repaint();

   }

}
//class PanelControl从文本框输入参数

class PanelControl extends JPanel implements ActionListener,FocusListener
{

    Dda frame;
    JTextField[] setting = new JTextField[4];
    PanelControl(Dda parent,String[] label)
   {
       Dda frame=parent;
       GridLayout cGrid = new GridLayout(4,2,10,10);
       setLayout(cGrid);
       for(int i=0;i<4;i++)
      {
         setting[i] = new JTextField("1");
         setting[i].addFocusListener(this);
         setting[i].addActionListener(this);
         JLabel settingLabel = new JLabel(label[i]);
         add(settingLabel);
         add(setting[i]);
       }
         setVisible(true);
    }

     public void actionPerformed(ActionEvent evt)//事件处理
   {
      if (evt.getSource() instanceof JTextField)
      frame.draw(this);
    }
      public void focusLost(FocusEvent evt) 
    {
      frame.draw(this);
    }

     public void focusGained(FocusEvent evt) { } 

}

class Draw extends JPanel //画图类
{
     public void paintComponent(Graphics comp)
     {
         Graphics2D comp2D=(Graphics2D)comp;
         comp2D.setColor(Color.white);
         Rectangle2D.Float background=new Rectangle2D.Float(0F,0F,50F,50F);//以矩形为底版
         comp2D.fill(background); 
         comp2D.setColor(Color.black);
         GeneralPath line=new GeneralPath();//多边形类

         line.moveTo(Dda.x0,Dda.y0);

        int k=(Dda.y1-Dda.x1)/(Dda.y0-Dda.x0),y=Dda.y0;

          for(int x=Dda.x0;x<=Dda.x1;x+=1)
         {
            line.lineTo((int)x,(int)(y+0.5));
            y=y+k; 
          }
        comp2D.draw(line);

     }
}