drawjpanel.java

来自「32个java程序源代码」· Java 代码 · 共 96 行

// Exercise 21.13: DrawJPanel.java
// This class defines the DrawJPanel class.
import java.awt.*;
import java.awt.event.*;
import java.util.Random;
import javax.swing.*;

public class DrawJPanel extends JPanel
{
	// Random object to create random numbers
	private Random generator = new Random();

	int x;        // x position of circle
	int y;        // y position of circle
	int diameter; // diameter of circle

	// no-argument constructor
	public DrawJPanel()
	{
      // add MouseListener to DrawJPanel
		addMouseListener(

   		new MouseListener() // anonymous inner class
   		{
   			// event handler called when mouse button is pressed
   			public void mousePressed( MouseEvent event )
   			{
   				drawJPanelMousePressed( event );
   			}

            // event handler must exist to implement interface
            public void mouseReleased( MouseEvent event )
            {
            }

            // event handler must exist to implement interface
            public void mouseClicked( MouseEvent event )
            {
            }

            // event handler must exist to implement interface
            public void mouseEntered( MouseEvent event )
            {
            }

            // event handler must exist to implement interface
            public void mouseExited( MouseEvent event )
            {
            }
   
   		} // end anonymous inner class

		); // end call to new MouseListener

	} // end constructor

	// set dimensions of circle and call repaint
	private void drawJPanelMousePressed( MouseEvent event )
	{
      x = event.getX(); // get x position of mouse
      y = event.getY(); // get y position of mouse

      // set width to random int from 5 to 199
      diameter = 5 + generator.nextInt( 194 );

      repaint(); // repaint DrawJPanel

	} // end method drawJPanelMousePressed

	// draw circle
	public void paintComponent( Graphics g )
	{
      super.paintComponent( g );

      // draw circle
      g.setColor( Color.BLUE );
      g.drawOval( x, y, diameter, diameter );

	} // end method paintComponent

} // end class DrawJPanel

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