Solutions & Answers to Previous University Exam Questions
Question: Model a class 'Rectangle' with 'Length' and 'Breadth' that allows initialization by copying values from an already initialized instance[cite: 3].
class Rectangle {
double length;
double breadth;
// Parameterized Constructor
Rectangle(double length, double breadth) {
this.length = length;
this.breadth = breadth;
}
// Copy Constructor
Rectangle(Rectangle rect) {
this.length = rect.length;
this.breadth = rect.breadth;
}
void display() {
System.out.println("Length: " + length + ", Breadth: " + breadth);
}
}
public class Main {
public static void main(String[] args) {
Rectangle r1 = new Rectangle(10.5, 5.0); // Original
Rectangle r2 = new Rectangle(r1); // Copying instance
System.out.print("r1: "); r1.display();
System.out.print("r2: "); r2.display();
}
}Question: Create a 'Complex' class that uses constructor overloading to initialize complex numbers[cite: 3].
class Complex {
double real;
double imag;
// Default Constructor (0 + 0i)
Complex() {
this.real = 0.0;
this.imag = 0.0;
}
// Single Parameter (real number: real + 0i)
Complex(double real) {
this.real = real;
this.imag = 0.0;
}
// Two Parameters (real + imag i)
Complex(double real, double imag) {
this.real = real;
this.imag = imag;
}
void display() {
System.out.println(real + " + " + imag + "i");
}
}
public class Main {
public static void main(String[] args) {
Complex c1 = new Complex(); // 0.0 + 0.0i
Complex c2 = new Complex(5.5); // 5.5 + 0.0i
Complex c3 = new Complex(3.0, 4.2); // 3.0 + 4.2i
c1.display();
c2.display();
c3.display();
}
}Question: Explain the argument passing mechanism used in Java when an instance of a class is passed as an argument[cite: 3].
class Box {
int size = 10;
}
public class Main {
static void modifyBox(Box b) {
b.size = 50; // Modifies original object in heap memory
}
public static void main(String[] args) {
Box myBox = new Box();
System.out.println("Before: " + myBox.size); // Output: 10
modifyBox(myBox);
System.out.println("After: " + myBox.size); // Output: 50
}
}Question: What is a constructor? What are its uses? Is it possible to create an object using A ob = new A(); if class A contains ONLY parameterized constructors? Justify[cite: 3].
Constructor: A special member function used to initialize objects upon creation[cite: 3].
Uses: Assign initial values to instance attributes and allocate resources during object creation[cite: 3].
Is A ob = new A(); possible? NO[cite: 3].
Justification: The Java compiler automatically generates a default no-argument constructor ONLY if the class defines no constructors at all[cite: 3]. Once a parameterized constructor is defined explicitly, the compiler suppresses the automatic default constructor[cite: 3]. Thus, calling new A() without defining an explicit no-arg constructor causes a compilation error[cite: 3].
class A {
int val;
// ONLY parameterized constructor defined
A(int v) {
this.val = v;
}
}
public class Main {
public static void main(String[] args) {
// A ob = new A(); // COMPILATION ERROR: Constructor A() is undefined
A ob = new A(100); // Correct Usage!
}
}Question: Define a Queue class with a default constructor, parameterized constructor, enqueue, dequeue, and display functions[cite: 3].
class Queue {
private int arr[];
private int front, rear, capacity, count;
// Default Constructor (Default capacity = 5)
Queue() {
this(5);
}
// Parameterized Constructor
Queue(int size) {
arr = new int[size];
capacity = size;
front = 0;
rear = -1;
count = 0;
}
public void enqueue(int item) {
if (count == capacity) {
System.out.println("Queue Overflow!");
return;
}
rear = (rear + 1) % capacity;
arr[rear] = item;
count++;
}
public int dequeue() {
if (count == 0) {
System.out.println("Queue Underflow!");
return -1;
}
int x = arr[front];
front = (front + 1) % capacity;
count--;
return x;
}
public void display() {
if (count == 0) {
System.out.println("Queue is empty!");
return;
}
System.out.print("Queue elements: ");
for (int i = 0; i < count; i++) {
System.out.print(arr[(front + i) % capacity] + " ");
}
System.out.println();
}
}
public class Main {
public static void main(String[] args) {
Queue q = new Queue(3);
q.enqueue(10);
q.enqueue(20);
q.display(); // Output: 10 20
q.dequeue();
q.display(); // Output: 20
}
}Question: Create a class called 'Box' with length, breadth, and height, default and parameterized constructors, and a display volume method[cite: 3].
class Box {
double length, breadth, height;
// Default Constructor
Box() {
length = breadth = height = 1.0;
}
// Parameterized Constructor
Box(double l, double b, double h) {
length = l;
breadth = b;
height = h;
}
double getVolume() {
return length * breadth * height;
}
void displayVolume() {
System.out.println("Box Volume: " + getVolume());
}
}
public class Main {
public static void main(String[] args) {
Box defaultBox = new Box();
Box customBox = new Box(3.0, 4.0, 5.0);
defaultBox.displayVolume(); // Output: 1.0
customBox.displayVolume(); // Output: 60.0
}
}Question: Implement Java classes with suitable instance variables for (1) Bank, (2) Vehicle, and (3) Student[cite: 3].
// 1. Bank Class
class Bank {
String accountHolder;
double balance;
Bank(String accountHolder, double balance) {
this.accountHolder = accountHolder;
this.balance = balance;
}
}
// 2. Vehicle Class
class Vehicle {
String model;
int speed;
Vehicle(String model, int speed) {
this.model = model;
this.speed = speed;
}
}
// 3. Student Class
class Student {
String name;
int rollNo;
Student(String name, int rollNo) {
this.name = name;
this.rollNo = rollNo;
}
}Question: Discuss classes and objects in Java using a 'Student' object in a Student Management Application[cite: 3].
class Student {
// Attributes (State)
int studentId;
String name;
double gpa;
// Constructor
Student(int studentId, String name, double gpa) {
this.studentId = studentId;
this.name = name;
this.gpa = gpa;
}
// Method (Behavior)
char calculateGrade() {
if (gpa >= 3.5) return 'A';
else if (gpa >= 2.5) return 'B';
else return 'C';
}
void printStudentReport() {
System.out.println("ID: " + studentId + " | Name: " + name + " | Grade: " + calculateGrade());
}
}
public class Main {
public static void main(String[] args) {
// Instantiating Student Objects
Student student1 = new Student(101, "Alice", 3.8);
Student student2 = new Student(102, "Bob", 2.9);
student1.printStudentReport();
student2.printStudentReport();
}
}