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Slider Graph

This applet that draws the graph of a function that can include
references to the "constants" a, b, and c. The values of these
constants can be adjusted using the sliders at the bottom of the
applet. The applet responds to the mouse actions click, shift-click,
click-and-drag, and right-click-and-drag. I've added another
buttons to the limit control panel. The "Equalize Axes" button
adjusts the x- and y-limits so that the scales on the two axes
are the same.

The following source code shows how the applet is built from
JCM components. Most of the comments are for features that were
not already covered in previous examples.

import java.awt.*;
import edu.hws.jcm.data.*;
import edu.hws.jcm.draw.*;
import edu.hws.jcm.awt.*;

public class SliderGraph extends java.applet.Applet {

   private DisplayCanvas canvas;
   public void stop() {
   JCMPanel makeSliderPanel(VariableSlider v) {
         // A small utility routing that makes a JCMPanel that contains
         // a VariableSlider and a DisplayLabel that shows the value
         // of the variable associated with that slider.
      JCMPanel p = new JCMPanel();
      p.add(v, BorderLayout.CENTER);
      p.add( new DisplayLabel(v.getName() + " = #", new Value[] { v } ), BorderLayout.EAST);
      return p;

   public void init() {
      Parser parser = new Parser();
      Variable x = new Variable("x");
        // Create the three VariableSliders.  In this case, the sliders have
        //   names.  There is also a Variable associated with each slider, 
        //   which has the same name.  This variable is added to the parser
        //   which is passed as the fourth parameter to the constructor, making
        //   it possible to use "a", "b", and "c" in expressions parsed by the
        //   parser.  Adjusting the value on a slider changes the value of the
        //   associated variable, and therefore changes the value of any
        //   expression that refers to that variable.  The second and third
        //   parameters to the constructor give the minimum and maximum Values
        //   on the slider.  Passing "null,null" uses the defaults, namely
        //   new Constant(-5) and new Constant(5).
      VariableSlider a = new VariableSlider("a",null,null,parser);
      VariableSlider b = new VariableSlider("b",null,null,parser);
      VariableSlider c = new VariableSlider("c",null,null,parser);

      canvas = new DisplayCanvas();
      canvas.add(new Panner());
      LimitControlPanel limits =
           new LimitControlPanel( LimitControlPanel.SET_LIMITS | LimitControlPanel.RESTORE
                                    | LimitControlPanel.EQUALIZE,  false);
      ExpressionInput input = new ExpressionInput("a*x^2 + b*x + c", parser);
      Graph1D graph = new Graph1D(input.getFunction(x));
      ComputeButton button = new ComputeButton("Graph it!");
      canvas.add(new Axes());
      canvas.add(new DrawBorder(Color.darkGray, 2));
      JCMPanel main = new JCMPanel();  // Build interface out of JCMPanels!
      main.add(canvas, BorderLayout.CENTER);
      main.add(limits, BorderLayout.EAST);
      JCMPanel bot = new JCMPanel(5,1);
      main.add(bot, BorderLayout.SOUTH);
      bot.add(new Label("Enter a function f(x), which can use the constants a, b, and c:"));
      JCMPanel inputPanel = new JCMPanel();
      inputPanel.add(input, BorderLayout.CENTER);
      inputPanel.add(button, BorderLayout.EAST);
      bot.add( makeSliderPanel(a) );  // Create and add the sliders.
      bot.add( makeSliderPanel(b) );
      bot.add( makeSliderPanel(c) );
      Controller controller = main.getController();  // Set up error reporting.

      main.gatherInputs();  // Set up main panel to respond to changes in input objects.
                            // This works since the interface is built of JCMPanels.  For
                            // the same reason, I don't have to add the objects the the
                            // controller.
      button.setOnUserAction(controller);  // Set controller to respond to button.

      setLayout(new BorderLayout());

   } // end init()
} // end class SliderGraph

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