paintpanel.java

金旭亮的java教案

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Vector;

//绘图区
public class PaintPanel extends JPanel
                        implements MouseListener, MouseMotionListener,
                                   ActionListener {
   private Vector shapes;   // 图形集合
   private Shape currentShape;
   private String currentShapeType = "Line";   // default
   private Color currentColor = Color.black;
   Timer timer = new Timer( 40, this );

   public PaintPanel()
   {
      shapes = new Vector();   // creates empty Vector
      addMouseListener( this );
      addMouseMotionListener( this );
      setBackground( Color.white );
      timer.start();
   }
   
//重绘整个屏幕，由Repaint方法调用
   public void paintComponent( Graphics g )
   {
      super.paintComponent( g );

      Shape current;

      for ( int i = 0; i < shapes.size(); i++ ) {
         current = ( Shape ) shapes.elementAt( i );
         current.draw( g );
      }
   }

   public void actionPerformed( ActionEvent e )
   {
      repaint();//自动调用paintComponent（）
   }

   /*
      In the following method, we use features that have not been covered in
      the text. We could have used an if/else structure to choose which shape
      to create. Instead,

         Class c = Class.forName( currentShapeType );

      loads the class definition for the class with the String name stored in
      currentShapeType. The statement

         currentShape = (Shape) c.newInstance();

      creates a new instance of the class that was loaded. The next line adds
      the new shape to the Vector (at the end).

      The try/catch syntax is covered in chapter 14. It is required here
      because both the Class.forName method call and the c.newInstance method
      call can cause runtime exceptions (problems). In this case we are
      saying "if a runtime problem occurs, ignore it."
   */
   public void mousePressed( MouseEvent e )
   {
      try {        
      //注意创建实例的方法,CurrentShapeType是一个类型的变量
      //这种技术称为"反射"
       
         Class c = Class.forName( currentShapeType );
         currentShape = (Shape) c.newInstance();
         currentShape.setX1( e.getX() );
         currentShape.setY1( e.getY() );
         currentShape.setX2( e.getX() );
         currentShape.setY2( e.getY() );
         currentShape.setColor( currentColor );
         //加入到图形集合中
         shapes.addElement( currentShape );
      }
      catch (Exception ex) { ex.printStackTrace(); }
   }

   public void mouseReleased( MouseEvent e )
   {
      currentShape.setX2( e.getX() );
      currentShape.setY2( e.getY() );

      // NOTE: We should store these for termination later.
      MovingShape mover =
         new MovingShape( currentShape, this,
                          (int)(Math.random() * 5 + 1),
                          (int)(Math.random() * 5 + 1) );
      //启用多线程执行，调用Run方法，生成图形的坐标
      mover.start();

      repaint();
   }

   public void mouseClicked( MouseEvent e )
   {

   }

   public void mouseEntered( MouseEvent e )
   {

   }

   public void mouseExited( MouseEvent e )
   {

   }

   public void mouseMoved( MouseEvent e )
   {

   }

//当鼠标拖动时，重绘图形
   public void mouseDragged( MouseEvent e )
   {
      currentShape.setX2( e.getX() );
      currentShape.setY2( e.getY() );
      repaint();
   }

   public void setCurrentShapeType( String s )
   {
      currentShapeType = s;
   }

   public void setCurrentColor( Color c )
   {
      currentColor = c;
   }
}