// DrawingFrameDemo.java
//howto do Graphics drawing in a JFrame by subclassing JPanel:
//define a customized subclass of JPanel that can do graphical drawing.

//widgets' event handler is 'this'.
//

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

public class DrawingFrameDemo  implements ActionListener {

    private JFrame outputFrame;
    private Container container;
    private DrawingPanel myDrawingPanel;   //***DrawingPanel is user-defined below
    private JButton drawButton;

    public static void main( String [] args ) {
  
	DrawingFrameDemo myDemo = new DrawingFrameDemo();
    }


    public DrawingFrameDemo() {
	outputFrame = new JFrame();
	outputFrame.setSize(600,500);
	outputFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	
	container = outputFrame.getContentPane();  
	container.setLayout( new BorderLayout() );  //for this demo

	//***create object of the customized subclass of JPanel
	myDrawingPanel = new DrawingPanel();  

	drawButton = new JButton( "Draw some random lines (click me)" );
	drawButton.addActionListener(this);

	container.add( myDrawingPanel, BorderLayout.CENTER );  
	container.add( drawButton, BorderLayout.SOUTH );

	outputFrame.setVisible(true);
    } 


    public void actionPerformed( ActionEvent event )
    {
	//***call of some method of the custom subclass of JPanel that calls repaint()
	myDrawingPanel.drawRandomLines();   
    }
    
}

//*** define a subclass (of whatever name) of JPanel.
class DrawingPanel extends JPanel {

    //***must be this signature.
    //***called explicitly by the repaint method and 
    //implicitly whenever the area is resized or uncovered.
    //analogous to the paint method of an applet.
    //all the Graphics drawing methods can be used:
    //drawLine, drawOval, fillOval, drawRect, fillRect, drawString, setColor, setFont...
    public void paintComponent( Graphics g )
    {
	super.paintComponent( g );     //clears the drawing area.
	int w=getWidth();     //***width of drawing area.
	int h=getHeight();    //***  Try resizing the frame window.
	//draw some random lines for demo purposes:
	for (int i=1; i<100; i++) {
	    g.setColor(new Color((int)(Math.random()*256),      //random color
				 (int)(Math.random()*256),
				 (int)(Math.random()*256)));
	    g.drawLine((int)(Math.random()*w),    //random start and end points
		       (int)(Math.random()*h),
		       (int)(Math.random()*w),
		       (int)(Math.random()*h));
	}
	
    }
    
    //***a method that calls repaint()
    public void drawRandomLines()
    {
	repaint();    //repaint() has paintComponent() called
    }
    
}