ObjectOriented Programming CCIT4023

Assignment 3 – Detailed Answers

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Section A (20 marks)

1. Answer: A) Array of String
   The main method signature is public static void main(String[] args).

2. Answer: C) Constructors
   Constructors are not inherited in Java.

3. Answer: B) Field
   Identifier resolution order: local variable → parameter → field.

4. Answer: D) All of the other answers
   ee.dept is a package, import is a keyword, and Div is a class.

5. Answer: D) this
   Used to call another constructor in the same class.

6. Answer: D) Overriding
   Allows a subclass to reimplement a superclass method.

7. Answer: B) It declares and creates an object of Pet array
   The array is created, elements are initialized to null.

8. Answer: B) "06"
   36 % 6 = 0, then 0 + "6" results in "06".

9. Answer: D) All of the other answers
   All options declare arrays.

10. Answer: A) 412
    doubleA.length = 4, "4" + "12" results in "412".

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Section B (40 marks)

1(a) Three Major OOP Features (6 marks)

• Encapsulation: Bundling data and methods together while restricting access using access modifiers.
• Inheritance: Allowing a subclass to reuse and extend the properties and methods of a superclass.
• Polymorphism: Allowing objects to take multiple forms through method overriding.

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1(b) Operator Evaluation (4 marks)

i. d >= c && e != a - c <= d + b
- First evaluated operator: -
- Last evaluated operator: &&

ii. a == d % b || d < b && c <= b
- First evaluated operator: %
- Last evaluated operator: ||

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2. Class Card (15 marks)

public class Card {
    public String cName;
    protected int cCode;

    Card(String inName, int inCode){
        cName = inName;
        cCode = inCode;
    }
}

2(a) Visibility Modifiers (2 marks)

• public
• protected
• default (package-private)

2(b) Primitive and Reference Types (2 marks)

• Primitive: int
• Reference: String, Card

2(c) UML Class Diagram (5 marks)

-------------------------
|        Card           |
-------------------------
| + cName : String      |
| # cCode : int         |
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| Card(String, int)     |
-------------------------

2(d) getInfo() Method (3 marks)

public String[] getInfo() {
    String[] info = new String[2];
    info[0] = cName;
    info[1] = String.valueOf(cCode);
    return info;
}

String str = "456"; int num = Integer.valueOf(str);

2(e) dspInfo() Method (3 marks)

public void dspInfo() {
    System.out.println("Card Name: " + cName + "; Card Code: " + cCode);
}

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3. Subclass MyCard (15 marks)

public class MyCard extends Card {  // MyCard inherits Card class

    public static final int DEF_CCODE = 23357;
    public String abc;
    public MyCard(String name, int code) {
        super(name, code);
    }

    public MyCard(String name) {
        this(name, DEF_CCODE);  // this.MyCard(name, DEF_CODE);
        this.abc = "sdfsdf";
    }

    public static void main(String[] args) {
        Card[] cards = new Card[4];
        Card newCard = new MyCard("TestCard", 2200);
        newCard.abc = "sfsdfa";

        cards[0] = new Card("cdA", 2134);
        cards[1] = new Card("cdB", 2135);
        cards[2] = new Card("cdC", 2136);
        cards[3] = new MyCard("cdD");

        for (int i = 0; i < cards.length; i++) {
            cards[i].dspInfo();
        }
    }
}

Sample Output

Card Name: cdA; Card Code: 2134
Card Name: cdB; Card Code: 2135
Card Name: cdC; Card Code: 2136
Card Name: cdD; Card Code: 23357

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