// VariablesDemo2Panel.java
// Custom panel which demonstrates paint method and
// exemplifies difference between static and instance
// variables.
//
// Intended to be used with VariablesDemo2.java

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

/**
 * Custom panel which, whenever it is painted,
 * talks to two separate text fields (not
 * necessarily attached to this panel) to
 * display up-to-date counts of (1) the
 * number of objects of this class and
 * (2) the number of times this panel has
 * been painted.  It also talks to the
 * window's title bar to display count
 * of panels of this class when this
 * panel is created.
 *
 * @author D. Nixon
 */
public class VariablesDemo2Panel extends JPanel
{
   /**
    * Window which displays this panel
    */
   private VariablesDemo2 window;

   /**
    * Count of times this panel has been painted
    */
   private int paintCount = 0;

   /**
    * Count of objects of this class
    */
   private static int objectCount = 0;

   /**
    * Creates a custom panel that can talk to
    * the specified GUI components.
    *
    * @param window frame whose title bar will
    *         display count of objects of this
    *         class when this panel is created
    * @param objectCountField text field that will
    *         display count of objects of this
    *         class when this panel is painted
    * @param paintCountField text field that will
    *         display count of times this panel
    *         has been painted
    */
   public VariablesDemo2Panel(VariablesDemo2 window)
   {
      // Enable this panel to talk to its window:
      this.window = window;

      // This panel hasn't been painted yet
      paintCount = 0;

      // Increment count of objects created
      // via calls to this constructor.
      VariablesDemo2Panel.objectCount++;

      // Use window's title bar to display how many
      // panels of this class have been created so far:
      window.setTitle("Window #" + objectCount);
   }  // constructor

   /**
    * The paint method is called automatically
    * whenever this panel is painted.
    *
    * @param g an object that can draw on this panel
    */
   public void paint( Graphics g )
   {
      // Distances in pixels from top left corner of this panel
      int pixelsFromLeft = 20;
      int pixelsFromTop = 20;

      // Dimensions, in pixels, of a big fat X to
      // be drawn on this panel:
      int width = 280;
      int height = 130;

      // Draw a red line from top left to bottom right
      // of this panel:
      g.setColor(Color.red);
      g.drawLine(pixelsFromLeft, pixelsFromTop,
                 pixelsFromLeft + width, pixelsFromTop + height);

      // Draw a blue line from top right to bottom left
      // of this panel:
      g.setColor(Color.blue);
      g.drawLine(pixelsFromLeft + width, pixelsFromTop,
                 pixelsFromLeft, pixelsFromTop + height);

      // Increment count of times this paint function
      // has been called:
      paintCount++;

      // Display up-to-date messages in text fields:
      window.setTopText("There are "
                        + VariablesDemo2Panel.objectCount
                        + " of us.");
      window.setBottomText("I've been painted "
                           + paintCount + " time"
                           + ((paintCount==1)?"":"s")
                           + ".");
   }  // method paint(Graphics)
}  // class VariablesDemo2Panel