Dear all,

 

I hope by now all of you have received the result of your first lab. Regarding your third lab, if you still have difficulties, you can ask questions to me through this e-mail. Okay, now I’ll talk a bit about the programming exercise I gave in yesterday’s class. I see some of you managed to do it well and can complete the program in the class but some of you still struggling, especially with the concept of Class in Java. I’ve uploaded the solution of the programming exercise here:

http://www.comp.nus.edu.sg/~johannes/ex1answer.zip

 

Okay, I’ll give some explanations about the solution:

1.       The first class which you need to implement is Jam Class. There are three data members in this class, i.e.: typeOfFruit, cannedDate, and size. Your first task is actually to fill in the default constructor with any default values and then determine whether this class needs another constructor or not. Actually, this class is better if you add another constructor:

  public Jam (String type, String date, int size) {

    this.typeOfFruit = type;

    this.cannedDate = date;

    this.size = size;

  }

If you didn’t add this constructor, when you create an instance of this class, you need to do the following:

Jam j1 = new Jam (); // calling the default constructor

// then you need to change the data members using the mutator

j1.setTypeOfFruit(“Blueberry”);

j1.setCannedDate(“1 September 2007”);

j1.setSize(10);

 

But, if you add the constructor above, your life will be easier. You only need one line to do the above operations:

Jam j1 = new Jam (“Blueberry”, “1 September 2007”, 10);

 

2.       After you implement the constructors, you need to complete all the class’ accessors and mutators:

  public String getTypeOfFruit () {

    return this.typeOfFruit;

  }

 

  public String getCannedDate () {

    return this.cannedDate;

  }

 

  public int getSize () {

    return this.size;

  }

 

  public void setTypeOfFruit (String type) {

    this.typeOfFruit = type;

  }

 

  public void setCannedDate (String date) {

    this.cannedDate = date;

  }

 

  public void setSize (int size) {

    this.size = size;

  }

 

3.       After that, implement the isEmpty() method and spread(int fluidOz) method

For isEmpty() method, this method should return true if size == 0, and false otherwise

For spread(…) method, this method should return true if the amount of jam to be spread is larger or equal with the current amount of jam, and false otherwise:

  public boolean spread ( int fluidOz ) {

    if (!isEmpty()) {

      // if the jam is not empty, we need to check the current amount against the amount to be spread

      if (fluidOz <= size) {

        size = size - fluidOz;

        return true;

      } else {

        // not enough jam to be spread

        return false;

      }

    } else

      // if the jam is empty, of course we can’t do this operation and just return false directly

      return false;

  }

 

4.       Yup, that’s all for Jam Class. After that, your task is to finish the implementation of Pantry Class. Pantry Class will store three jars of jam, therefore inside Pantry class, there are three objects of Jam class.

You first need to implement the second constructor, to set all the jams in the Pantry class:

  public Pantry (Jam jam1, Jam jam2, Jam jam3) {

    this.jam1 = jam1;

    this.jam2 = jam2;

    this.jam3 = jam3;

  }

 

5.       After you’ve finished implementing the constructor, you need to complete all the class’ accessors and mutators, just like the one you did inside Jam class

6.       Then, you need to implement select(int jamNumber) method. Since this class simulates the behavior of real life pantry, before you can spread jams over a bread, you need to select which jam you want to use right? Then you use select (int jamNumber) method to simulate this operation:

  public void select (int jamNumber) {

    switch (jamNumber) {

      // here, you use switch-case statement

      case 1: this.selectedJam = jam1; break;

      case 2: this.selectedJam = jam2; break;

      case 3: this.selectedJam = jam3; break;

      default: this.selectedJam = jam1;

    }

  }

 

7.       Lastly, implement the spread() method. Basically, this method do the spread method in the selected jam:

  public boolean spread (int fluidOz) {

    return selectedJam.spread(fluidOz);

  }

 

8.       After you’ve finished implementing Jam and Pantry classes, implement the main method in Ex1Main.java to run the simulation J

 

Okay, that’s for the programming exercise. If you still have any questions, you can ask me. If you need a special consultation time with me (I mean, meeting face-to-face), you can ask me to arrange one for you. My Wednesday and Friday are free J

 

Now, let’s talk about your upcoming Term Test #1. You can find the information about this here: http://www.comp.nus.edu.sg/~cs1101x/3_ca/termtests.html

Basically, the format should be MCQ, but I don’t know how many questions are there for this semester. In that website as well, you can find the term test questions and answers from previous years. You can try those as an exercise; don’t look at the answer first! If you don’t know why the answer is like that, you can ask me for explanation. In the next discussion (1 October 2007), I’ll go through some of difficult questions in the past years term tests. For your own practice, you can try to do all the questions in your textbook until Chapter 7. Try to do them and then if you are not sure about your answer, you also can ask me. So, ask me as many as you wish since I’m your tutor for this moduleJ.

 

Oh yes, one more thing, for your own self exercise, try to do the second and third exercise in Lab 3 as well.

Yup, that’s all from me. I think I’ve written a very long e-mail this time :p.