Aquarium Maintanance System - Java Help

Question

Hi,
I am not sure if this if this is the correct forum, however I need some advice on a project that I am doing.
I am creating a Aquarium Maintanance System, programming it in Java, however some problems arise for instance I do not have the sufficient hardware (thermometer, heater, filter etc.) to use with the Java so I can not demostrate to the person marking that it works correctly. The only thing that I can show is a an example of some of the functionality of the system by creating simulations in certain areas of the system.
What I need advice is, how do I tackle creating the system in Java without having the actual hardware to use, because it seems to me that it would be a system with a bunch of methods but hardly no code in them.
Thanks

Answer 1

This is where good design, division of responsibility, and the notion of layers becomes very handy.
Define a layer that interacts with the thermometer, etc. The layers above it don't know or care where that hardware interface layer gets its input from, or where it sends its output. For testing without the actual hardware, you create a ThermometerSimulator class that you control, and that feeds its data "upward" just like a real thermometer would.
package aquarium.io;
public interface Thermometer {
  int getTemperature();
package aquarium.sim;
public class ThermometerSimulator implements Thermometer {
  private int temp;
  public int getTemperature() {
    return temp;
  public int setTemperature(int temp) {
    this.temp = temp;
package aquarium.hardware;
public class RealThermometer imlements Thermometer {
  public int getTemperature() {
    // code to read from the hardware and return it
}During testing, you can have a controller that sets the temp on your thermometer simulator, and then your real code will read that temp, call heater.turnOn if it's too low, etc. The HeaterSimulator then can, for example, sleep for 10 seconds, call ThermometerSimulator.incrementTemp(1), sleep for 10, increment, etc. to simulate the heater warming up the water. The real Heater of course won't interact directly with the water thermometer, it will just send on/off signals to your heater hardware, which will warm the real water, which will affect that values that the real hardware thermometer returns in its get() call.
Note that your application that sits above that io layer will only ever care about the interfaces for Thermometer, Heater, etc., not the Simulator or Real classes.
Also note that I deliberately gave the Thermometer interface only a getTemp() method, not a set. The reason is that the user of a thermometer can only read the temp. You can't just set it to 85°. The various implementations will of course have ways to control what they return from get, for example the Simulator having a direct setter and a member variable. The real class that interacts with the hardware might just have its get method do something like
public int getTemp() {
  return vendorsHardwareInteractionLibrary.readTempFromDevice();
}Edited by: jverd on Oct 6, 2010 12:48 PM