Level 6 — Programming — Jul/Aug 2024 — Written

Question 1

Answer

int sum = 0;
for (int x = 0; x <= 5; x++) {
    sum += x;
}
System.out.println("The sum is: " + sum);

Question 2

Answer

• Primitive types hold values such as int, double, boolean and char.
• Reference types refer to objects, including classes such as String, arrays and interfaces. A reference can be null.

Question 3

Answer

• Graphical desktop applications.
• Business/accounting systems.
• Games and simulations.
• Mobile applications and reusable service libraries.

Question 4

Answer

Source code is the programmer-readable text written in a language such as Java. Machine code is processor-specific binary instructions executed by the hardware. Java normally first compiles to JVM bytecode, which the JVM interprets or JIT-compiles.

Question 5

Answer

class Student { String name; }
// Inside a method:
Student learner = new Student();

Student is a class defining structure/behaviour; learner refers to one object created from that class.

Question 6

Answer

class Animal {
    void eat() { System.out.println("Eating"); }
}
class Dog extends Animal {
    void bark() { System.out.println("Barking"); }
}

Animal is the base/superclass. Dog is derived and inherits the accessible eat() method while adding bark().

Question 7

Answer

• Polymorphism allows a common interface/reference to invoke behaviour appropriate to an actual object, for example an overridden draw() method on different Shape subclasses.
• Abstraction exposes necessary operations while hiding implementation details, for example a Shape interface declaring draw() without specifying how every shape is drawn.

Question 8

Answer

• java.lang — core classes such as String and Math; automatically imported.
• java.util — collections, Scanner and other utilities.
• java.io — stream/file I/O classes.

Question 9

Answer

A simple if executes its body only when its condition is true. if…else chooses one branch when true and the other when false.

Question 10

Answer

• Local variables declared within a method/block.
• Instance fields belonging to each object.
• Static/class fields shared by instances of a class.

Question 11

Answer

• Explain why a non-obvious algorithm or decision is necessary.
• Document a method’s purpose, expected inputs or important constraints.

Question 12

Answer

• Reuses accessible superclass behaviour rather than duplicating it.
• Supports extension and substitutability through overridden methods and polymorphic references.

Question 13

Answer

• Source-code editor.
• Projects/files explorer.
• Debugger and output/build console.

Question 14

Answer

1. Planning/feasibility: define scope, cost, resources and viability.
2. Requirements analysis: document users, workflows, records, access and reporting needs.
3. Design: specify data structures, interfaces, components and controls.
4. Implementation: write/configure the system.
5. Testing: verify functions, integration, security and acceptance criteria.
6. Deployment: migrate validated data, train users and release the system.
7. Maintenance: correct defects and improve the system as requirements change.

• JVM bytecode supports portability across compatible platforms.
• Object-oriented classes/interfaces support modular design and reuse.
• Automatic memory management and exception handling assist reliable development; neither removes the need for testing.

Question 15

Answer

Save as AddNumbers.java.

import java.util.Scanner;
public class AddNumbers {
    static double addNumbers(double a, double b) { return a + b; }
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.print("Enter a and b: ");
        double a = in.nextDouble(), b = in.nextDouble();
        System.out.println("Sum = " + addNumbers(a, b));
    }
}

• Arithmetic operators such as +, -, * and / calculate values.
• Relational operators such as = and == compare values.
• Logical operators such as &&, || and ! combine/invert boolean conditions.

int whole = 25;
double widened = whole;    // widening conversion
int narrowed = (int) 25.9; // explicit narrowing; result 25

Widening numeric conversion is generally implicit, though precision can be lost in some conversions. Narrowing needs a cast and can truncate or lose range/precision.

Question 16

Answer

• public: accessible wherever the enclosing type/module permits access.
• protected: accessible in the same package and in subclasses, subject to Java’s cross-package subclass rules.
• Package-private (no access keyword): accessible within the same package.
• private: accessible within the declaring class and its permitted nested/enclosing-class context.

Save as CompareValues.java.

public class CompareValues {
    public static void main(String[] args) {
        int a = 4;
        int b = 9;
        int min = (a < b) ? a : b;
        System.out.println(min);
    }
}

Fix the main method signature, statement semicolons, missing declaration/assignment of min and missing closing braces. Output: 4.

switch (choice) {
    case 1:
        System.out.println("First");
        break;
    case 2:
        System.out.println("Second");
        break;
    default:
        System.out.println("Other");
}

Question 17

Answer

Because the condition is tested after the body, a do…while executes at least once.

Save as Temperature.java.

import java.util.Scanner;
public class Temperature {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.print("Celsius: ");
        double celsius = in.nextDouble();
        double fahrenheit = celsius * (9.0 / 5.0) + 32;
        System.out.printf("Fahrenheit = %.2f%n", fahrenheit);
    }
}

• Single inheritance: one subclass extends one superclass.
• Multilevel inheritance: a subclass extends a class that already extends another class.
• Hierarchical inheritance: several subclasses extend one superclass.
• Multiple interface inheritance/implementation: a class can implement several interfaces. Java does not support extending multiple classes.