Developing Java Beans

A Sample Simulator Applet

Let’s create a sample applet class called SimulatorSample that uses the Beans we created for the simulator. The applet will create instances of Temperature, Thermostat, Boiler, and Cooler, and make the required connections so that they work together. This is a pretty simple process. All of the work is done in the applet’s init() method. Everything else is handled by the objects themselves.

import java.applet.*;
import java.awt.*;
import BeansBook.Simulator.*;
import java.beans.*;

// the SimulatorSample applet class
public class SimulatorSample extends Applet
{
   // the applet init method
   public void init()
   {

The applet uses a simple flow layout, which is set up by calling the setLayout() method. Next, the simulator Beans are created by calling their default constructors. The three visual Beans are then added to the applet by passing each as a parameter to the applet’s add() method.

// use a flow layout, with components centered, and a 20 pixel 
      // separation between components
      setLayout(new FlowLayout(FlowLayout.CENTER, 20, 20));

      // create a temperature
      Temperature t = new Temperature(); 
      
      // create a thermostat     
      Thermostat th = new Thermostat();

      // create a cooler
      Cooler c = new Cooler();
      
      // create a boiler
      Boiler b = new Boiler();

      // add the thermostat, cooler, and boiler to the applet      
      add(th);
      add(c);
      add(b);

Now that all of the objects have been created, we need to wire them up. The Thermostat monitors changes to the Temperature object’s Temperature property ...