Java

OOP GUIDE / WORK

LAMP CLASS

Topics

• Instance variable of type Boolean
• Using encapsulation

TASK – PART 1 – LAMP CLASS WITHOUT ENCAPSULATION

Create the class named Lamp that will represent a lamp object. It has the following specification:

INSTANCE VARIABLES

• public boolean isOn;
  
  When isOn is true, the lamp is on. When isOn is false, the lamp is off.

• public int onCounter;
  
  OnCounter will be used to count the number of times that the lamp is switched on.

CONSTRUCTOR

• There is a constructor that gets no parameters. It creates a lamp that is off with an onCounter set to zero.

INSTANCE METHODS

• A toString() method that returns a String in the following form: "The lamp is ON. It has been switched on 8 times".
  
  

TASK – PART 2 – TESTING THE LAMP CLASS

Create a LampTester class. Inside main, create a lamp object.

Update the instance variables and use the toString() method to output the lamp’s state.

Notice that we have to be careful to always update onCounter when we turn on the lamp. The current code setup means that we are responsible for keeping the onCounter’s value accurate. This is not good design! We want to object to do this automatically for us.

The solution to this problem is to use Encapsulation. We will do this in the next steps.

TASK – PART 3 – SETUP

We will be changing the Lamp class and the LampTester class. So we will make copies so that you can later compare the initial class with the encapsulated one.

• Create a package named lamp01.
• Move your Lamp and LampTester classes into package lamp01.
• Create a package names lamp02.
• Make copies of the Lamp and LampTester classes and paste them into package lamp02.
• Close all your open files and open the classes in lamp02.

TASK – PART 4 – ENCAPSULATED LAMP CLASS

We want the instance variable onCounter to automatically update when the lamp is turned on. We do this by making the instance variables private and providing needed access with instance methods.

INSIDE LAMP.JAVA

• Make the instance variables onCounter and isOn private.
  
  
• Add a switchOn() method. It makes isOn become true. It should also update onCounter.
  
  
• Add a switchOff() method. It makes isOff become false.

INSIDE LAMPTESTER.JAVA

• Notice that the LampTester class contains errors now because the old code is trying to directly access the instance variables which are no longer public. Remove the statements that are errors.

• Test both the switchOn() and switchOff() methods. Be sure to output the lamp’s state to make sure that things are working as expected.

ADDITIONAL CHANGES

• Did you deal with the case where you might switchOn() your lamp several times in a row?

• Notice that you can only see the state of the lamp’s instance variable using toString() at the moment. It would probably be a good idea to have get methods for both isOn and onCounter.

• Provide a getIsOn() method.

• Provide a getOnCounter() method.
  
  
• It might be useful to have a method that simply returns “ON” or “OFF” depending on the state of the lamp. Provide at getState() method that does this.