drawjpanel.java

金旭亮的java教案

// DrawJPanel.java
//此类用于提供绘图表面
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

//从JPanel中派生出一个绘图面板
public class DrawJPanel extends JPanel
{
   // 鼠标的当前座标
   private Point currentPoint;

   // 绘制图形的颜色
   private final Color DRAW_COLOR = Color.BLUE;
   private final int DRAW_DIAMETER = 8;//绘制线条宽度

   // 用于擦除图形的背景色
   private final Color ERASE_COLOR = getBackground();
   private final int ERASE_DIAMETER = 8;

   // 用于绘制圆的颜色和线宽
   private Color drawColor;
   private int drawDiameter;
   
   // 构造函数
   public DrawJPanel()
   {
      addMouseListener(

         new MouseListener() // 匿名内部类，对鼠标点击进行响应
         {
            // 单击
            public void mouseClicked( MouseEvent event )
            {
            }

            // 鼠标进入
            public void mouseEntered( MouseEvent event )
            {
            }

            // 鼠标离开
            public void mouseExited( MouseEvent event )
            {
            }

            // 按下鼠标按钮
            public void mousePressed( MouseEvent event )
            {
               drawJPanelMousePressed( event );
            }

            // 松开鼠标按钮
            public void mouseReleased( MouseEvent event )
            {
            }

         } // end anonymous inner class

      ); // end call to addMouseListener

	  //响应鼠标移动
      addMouseMotionListener(

         new MouseMotionListener() 
         {
            // 拖动鼠标
            public void mouseDragged( MouseEvent event )
            {
               drawJPanelMouseDragged( event );
            }

            // 鼠标移动,必须写，这是由接口规定的
            public void mouseMoved( MouseEvent event )
            {
            }

         } // end anonymous inner class

      ); // end call to addMouseMotionListener

   }  // end constructor

   // 当鼠标按下时画一个小圆
   private void drawJPanelMousePressed( MouseEvent event )
   {
      // 获取鼠标当前所在位置
      currentPoint = event.getPoint();

      if ( event.isMetaDown() ) // 按下右键
      {
      	//准备清除画面
         drawColor = ERASE_COLOR;
         drawDiameter = ERASE_DIAMETER;
      }
      else // 按下左键，准备绘图
      {
         drawColor = DRAW_COLOR;
         drawDiameter = DRAW_DIAMETER;
      }

      repaint(); // 重绘屏幕，将会导致paintComponent（）方法被调用

   } // end method drawJPanelMousePressed

   // 在鼠标当前位置画一个小圆，覆盖了JComponent的同名方法
   public void paintComponent( Graphics g )
   {
      g.setColor( drawColor ); // set the color

      if ( currentPoint != null )
      {
         // 画圆
         g.fillOval( currentPoint.x, currentPoint.y, 
            drawDiameter, drawDiameter );
      }

   } // end method paintComponent

   // 鼠标拖动
   private void drawJPanelMouseDragged( MouseEvent event )
   {
      // store the location of the mouse
      currentPoint = event.getPoint();

      repaint(); //重绘屏幕
   } // end method drawJPanelMouseDragged

} // end class DrawJPanel

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