Q: Explain why Java is Secure, Portable, and Dynamic?

Which concept in Java

ensures these?

1. Java is Secure because:

• Java does not use pointers (which can lead to memory access issues).

• Runs in the Java Virtual Machine (JVM) – avoids direct access to system memory.

• Has Security Manager and bytecode verification.

• Supports exception handling, preventing unexpected crashes.

• Classes from unknown sources are verified before execution.

Concept responsible:

• Bytecode Verification

• JVM (Java Virtual Machine)

• Security Manager

2. Java is Portable because:

• Java code is compiled into Bytecode, not machine code.

• This Bytecode can run on any system with JVM (Windows, Linux, Mac, etc.)

• "Write once, run anywhere" is Java’s motto.

Concept responsible:

• Bytecode

• JVM (Platform independence)

3. Java is Dynamic because:

• Supports dynamic loading of classes at runtime.

• Uses Reflection API to inspect and modify code at runtime.

• Can link code during runtime, not just compile-time.

Concept responsible:

• Class Loader

• Dynamic Linking

• Reflection
 Conclusion:

Java is secure, portable, and dynamic mainly because of the JVM, Bytecode, and class-loading
mechanisms. These features make Java platform-independent, safe, and adaptable.

What are strings in java? Explain following operations of class strings in java with example.
[9] i) ii) iii) To find length of string To compare strings Extraction of characters from string
iv) To search a substring

What are Strings in Java?

• A String is a group of characters enclosed in double quotes.

• In Java, strings are objects of the String class.

• Strings are immutable, meaning their value cannot be changed after creation.

• Java provides many methods to work with strings.

i) To Find Length of String

Theory:

• The .length() method returns the number of characters in the string.

• Spaces are also counted.

Example:

java

CopyEdit

String str = "Java Programming";

int len = str.length();

System.out.println("Length: " + len);

Output:
Length: 16

ii) To Compare Strings

Theory:

• .equals() checks if two strings are exactly same (case-sensitive).

• .compareTo() compares two strings alphabetically.

Example:

java
CopyEdit

String s1 = "Java";

String s2 = "Java";

System.out.println(s1.equals(s2)); // true

Output:
true

iii) Extraction of Characters from String

Theory:

• The .charAt(index) method is used to get a single character from the string.

• Index starts from 0.

Example:

java

CopyEdit

String word = "Hello";

char ch = word.charAt(1);

System.out.println("Character at index 1: " + ch);

Output:
Character at index 1: e

iv) To Search a Substring

Theory:

• The .indexOf("substring") method returns the starting position of a word inside a string.

• Returns -1 if not found.

Example:

java

CopyEdit

String sentence = "Java is fun";

int index = sentence.indexOf("fun");

System.out.println("Position: " + index);

Output:
Position: 8
Question:

What is a constructor? Show with example the use and overloading of default, parameterized, and copy
constructor?

Answer 1: In Simple English Only

What is a Constructor?

• A constructor is a special method used to initialize objects.

• It has the same name as the class and no return type.

• It is called automatically when an object is created.

Types of Constructors:

1. Default Constructor:

• Takes no parameters.

• Sets default values to object properties.

2. Parameterized Constructor:

• Takes parameters to initialize object with given values.

3. Copy Constructor:

• Creates a new object by copying data from an existing object.

Example of Constructor Overloading (All three types):

java

CopyEdit

class Student {

int id;

String name;

// Default constructor

Student() {

id = 0;

name = "Unknown";

}
 // Parameterized constructor

Student(int i, String n) {

id = i;

name = n;

// Copy constructor

Student(Student s) {

id = s.id;

name = s.name;

void display() {

System.out.println("ID: " + id + ", Name: " + name);

public class Main {

public static void main(String[] args) {

Student s1 = new Student(); // default constructor

Student s2 = new Student(101, "Alice"); // parameterized constructor

Student s3 = new Student(s2); // copy constructor

s1.display();

s2.display();

s3.display();

Output:
yaml

CopyEdit

ID: 0, Name: Unknown

ID: 101, Name: Alice

ID: 101, Name: Alice

Question:

What do you mean by method overloading? Demonstrate through a program in Java how method overloading
is used to add two integers and three integers respectively.

Answer 1: In Simple English Only (With Extra Theory Points)

What is Method Overloading?

• Method overloading is a feature that allows more than one method to have the same name but with
different parameters (either in number or type) inside the same class.

• It helps to increase the readability of the program by using the same method name for similar
actions.

• The return type can be the same or different, but the method signature must differ.

• It is a way of compile-time polymorphism or static polymorphism in Java.

• The compiler decides which method to call based on the number or type of arguments passed.

Example: Adding Two and Three Integers Using Method Overloading

java

CopyEdit

class Calculator {

// Method to add two integers

int add(int a, int b) {

return a + b;

// Overloaded method to add three integers

int add(int a, int b, int c) {

return a + b + c;

}
}

public class Main {

public static void main(String[] args) {

Calculator calc = new Calculator();

int sum1 = calc.add(10, 20); // Calls method with 2 parameters

int sum2 = calc.add(10, 20, 30); // Calls method with 3 parameters

System.out.println("Sum of two numbers: " + sum1);

System.out.println("Sum of three numbers: " + sum2);

Output:

yaml

CopyEdit

Sum of two numbers: 30

Sum of three numbers: 60

Question:

Explain following features of Java in detail:

i) Security
ii) Platform Independence
iii) Object-oriented

Answer 1: In Simple English Only

i) Security

• Java provides a secure environment for running applications.

• It has built-in security features like bytecode verification, sandboxing, and no direct access to
memory.

• Java programs run inside a Java Virtual Machine (JVM), which prevents harmful operations.

• It protects the system from viruses and malicious programs.

ii) Platform Independence

• Java is platform-independent because of its “Write Once, Run Anywhere” capability.

• Java code is compiled into bytecode, which can run on any system having JVM.

• JVM acts as a bridge between the bytecode and the operating system, making Java portable.

• This means the same Java program runs without changes on Windows, Linux, Mac, etc.

iii) Object-oriented

• Java follows the Object-Oriented Programming (OOP) concept.

• Everything in Java is based on objects and classes.

• It supports key OOP principles:

o Encapsulation: Hiding data using classes.

o Inheritance: One class inherits properties of another.

o Polymorphism: One method behaves differently based on objects.

o Abstraction: Showing only important details, hiding complexity.

• This makes Java programs modular, reusable, and easy to maintain.

Question:

Write short note on:

i) Garbage Collector
ii) this

Answer 1: In Simple English Only

i) Garbage Collector

• Garbage Collector (GC) in Java automatically removes unused objects from memory.

• It helps to free up memory by deleting objects that are no longer referenced.

• This prevents memory leaks and improves program performance.

• Programmers don’t need to manually free memory like in other languages.

ii) this

• this is a keyword in Java used to refer to the current object.

• It helps to distinguish between instance variables and parameters when they have the same name.
 • It can be used to call another constructor in the same class (this()), or access current object’s fields
and methods.

Question:

Define constructor. Which are the types of constructor used in Java? Explain with example.

Answer 1: In Simple English Only

What is a Constructor?

• A constructor is a special method in Java used to create and initialize objects.

• It has the same name as the class and no return type.

• It is automatically called when an object is created.

Types of Constructors in Java:

1. Default Constructor

o Takes no parameters.

o Sets default values to object fields.

2. Parameterized Constructor

o Takes parameters to initialize the object with user-defined values.

3. Copy Constructor

o Creates a new object by copying values from another object.

Example of All Three Constructors:

java

CopyEdit

class Student {

int id;

String name;

// Default Constructor

Student() {

id = 0;

name = "Unknown";
 }

// Parameterized Constructor

Student(int i, String n) {

id = i;

name = n;

// Copy Constructor

Student(Student s) {

id = s.id;

name = s.name;

void display() {

System.out.println("ID: " + id + ", Name: " + name);

public class Main {

public static void main(String[] args) {

Student s1 = new Student(); // Default constructor

Student s2 = new Student(101, "Ravi"); // Parameterized constructor

Student s3 = new Student(s2); // Copy constructor

s1.display();

s2.display();

s3.display();

}
Output:

yaml

CopyEdit

ID: 0, Name: Unknown

ID: 101, Name: Ravi

ID: 101, Name: Ravi

Question:

Explain following features of Java in detail:

i) Portability
ii) Architecture Neutral
iii) Distributed

Answer 1: In Simple English Only

i) Portability

• Java programs are portable, meaning they can run on any platform without changes.

• Java code is compiled into bytecode, not machine code.

• Bytecode can be run on any machine that has a Java Virtual Machine (JVM).

• This makes Java programs easy to move between Windows, Linux, and other systems.

ii) Architecture Neutral

• Java is architecture neutral, which means it does not depend on hardware or operating system.

• The bytecode generated by Java compiler can be run on any system with a JVM.

• So, Java code behaves the same way on all platforms, whether it's 32-bit or 64-bit system.

iii) Distributed

• Java supports distributed computing, meaning it can work across multiple computers over a network.

• It has built-in support for networking features using packages like java.net.

• Java programs can share data and files easily over the internet.

• It also supports technologies like Remote Method Invocation (RMI) and CORBA

Question:

Write short note on:

i) final
ii) finalize()
 Answer 1: In Simple English Only

i) final

• final is a keyword in Java used to make variables, methods, or classes unchangeable.

• Final variable: Value cannot be changed after initialization.

• Final method: Cannot be overridden by subclasses.

• Final class: Cannot be inherited by other classes.

• It is used to provide safety and control in code.

Example:

java

CopyEdit

final int x = 10;

// x = 20; // Error: cannot change final variable

ii) finalize()

• finalize() is a method in Java that is called by the Garbage Collector before destroying an object.

• It is used to clean up resources (like closing a file or database connection) before the object is
removed.

• It is defined in the Object class, so every class can override it.

• But it is rarely used now in modern Java because other methods like try-with-resources are better.

Example:

java

CopyEdit

protected void finalize() {

System.out.println("Object is destroyed");

Question:

Explain one-dimensional and multi-dimensional arrays used in Java with suitable examples.

Answer 1: In Simple English Only

What is an Array in Java?

 • An array is a collection of similar type of elements stored in a single variable.

• Arrays can be one-dimensional or multi-dimensional.

i) One-Dimensional Array:

• It is a linear array, like a list.

• Used to store values in a single row.

Syntax:

java

CopyEdit

int[] arr = new int[5];

Example:

java

CopyEdit

public class OneDArray {

public static void main(String[] args) {

int[] arr = {10, 20, 30, 40, 50};

for(int i = 0; i < arr.length; i++) {

System.out.println("Element at index " + i + ": " + arr[i]);

Output:

perl

CopyEdit

Element at index 0: 10

Element at index 1: 20

Element at index 2: 30

Element at index 3: 40

Element at index 4: 50

ii) Multi-Dimensional Array:

 • It stores data in rows and columns (like a table).

• The most common is a 2D array.

Syntax:

java

CopyEdit

int[][] arr = new int[2][3];

Example:

java

CopyEdit

public class MultiDArray {

public static void main(String[] args) {

int[][] arr = {

{1, 2, 3},

{4, 5, 6}

};

for(int i = 0; i < 2; i++) {

for(int j = 0; j < 3; j++) {

System.out.print(arr[i][j] + " ");

System.out.println();

Output:

CopyEdit

123

456

Question:

Describe primitive data types. List the primitive data types in Java and their respective storage capacity.

Answer 1: In Simple English Only

 What are Primitive Data Types?

• Primitive data types are the basic built-in data types in Java.

• They are not objects; they store simple values directly in memory.

• Java has 8 primitive data types.

List of Primitive Data Types in Java:

Data Type Description Size Example

byte Small integer 1 byte (8-bit) -128 to 127

short Short integer 2 bytes -32,768 to 32,767

int Integer (default) 4 bytes -2^31 to 2^31-1

long Large integer 8 bytes -2^63 to 2^63-1

float Decimal number (single) 4 bytes 3.4e−038 to 3.4e+038

double Decimal number (double) 8 bytes 1.7e−308 to 1.7e+308

char Single character 2 bytes 'A', 'B', '1'

boolean True/False value 1 bit true, false

Why use primitive data types?

• They are fast and memory efficient.

• Used when we only need to store a basic value like a number, character, or true/false.

Write short notes on Java Virtual Machine (JVM) with diagram.

Definition / Concept

• Java Virtual Machine (JVM) is a part of Java Runtime Environment (JRE).

• It is responsible for executing Java bytecode.

• JVM makes Java platform-independent by allowing the same bytecode to run on any device with JVM.

Key Points / Features of JVM:

• JVM runs the .class (bytecode) file generated by Java compiler.

• It provides security, memory management, and performance optimization.

• JVM is platform-dependent, but Java programs are platform-independent.

• It includes class loader, bytecode verifier, interpreter, and JIT compiler.

• It automatically handles garbage collection.

Question:

State the uses of the final keyword in Java.

Definition / Concept

• final is a keyword in Java used to make something unchangeable.

• It can be applied to variables, methods, and classes.

• Once declared as final, it cannot be modified or overridden.

Uses of final keyword in Java:

1. Final Variable

• Value can be assigned only once.

• Used to declare constants.

Example:

java

CopyEdit
final int SPEED_LIMIT = 60;

// SPEED_LIMIT = 70; // Error: cannot change final variable

2. Final Method

• Method cannot be overridden in a subclass.

• Provides safety in inheritance.

Example:

java

CopyEdit

class Vehicle {

final void run() {

System.out.println("Running safely");

3. Final Class

• Class cannot be extended (no subclass).

• Used for security and preventing modification.

Example:

java

CopyEdit

final class Bank {

void interestRate() {

System.out.println("Interest is 6%");

// class MyBank extends Bank { } // Error

Extra Points for Exam Writing:

• final improves security and stability in code.

• It prevents accidental changes to important parts of the program.

• Often used with static to create constants.

Example: static final double PI = 3.14;
• Final keyword is also used in inner classes and anonymous classes.

• Question:

• Define String in Java. Explain the following operations of class String in Java with example:
i) To find length of the string
ii) To compare two strings
iii) To extract a character from a string
iv) To concatenate two strings

• Definition / Concept

• A String in Java is a sequence of characters enclosed in double quotes (" ").

• Strings are objects of the String class.

• Java strings are immutable (they cannot be changed after creation).

• String Operations in Java

• i) To find length of the string

• The length() method returns the number of characters in a string.

• Example:

• java

• CopyEdit

• String name = "Java";

• System.out.println(name.length()); // Output: 4

• ii) To compare two strings

• Use equals() to compare actual content of two strings.

• Use == to compare reference (not recommended for content comparison).

• Example:

• java

• CopyEdit

• String s1 = "Hello";

• String s2 = "Hello";

• System.out.println(s1.equals(s2)); // Output: true

•

• iii) To extract a character from a string

• The charAt(index) method returns the character at the given index (starts from 0).

• Example:

• java

• CopyEdit

• String word = "Computer";

• System.out.println(word.charAt(3)); // Output: p

• iv) To concatenate two strings

• The concat() method or + operator is used to join two strings.

• Example:

• java

• CopyEdit

• String first = "Hello";

• String second = "World";

• System.out.println(first.concat(second)); // Output: HelloWorld

• System.out.println(first + " " + second); // Output: Hello World

• Extra Points for Exam Writing:

• String class is part of java.lang package.

• Strings are immutable – every modification creates a new string.

• Common string methods include: length(), charAt(), equals(), concat(), substring(), toUpperCase(), etc.

• Strings are widely used for text processing, display, and input in Java programs.

• Question:

• b) Explain Java’s role in Internet. Justify the following features of Java:

i) Architectural Neutral
ii) Distributed
iii) Secure

•
• Answer 1: In Simple English
•

• Java’s Role in Internet:

• Java lets programs run on any device connected to the Internet.

• Java applets run safely inside web browsers.

• It provides built-in networking tools for easy communication over the Internet.

• Java is widely used for web applications, online games, and mobile apps.

• i) Architectural Neutral:

• Java bytecode works on any hardware or operating system.

• Java programs are portable because they run on JVM on any platform.

• ii) Distributed:

• Java supports distributed computing where programs run on multiple machines connected by a
network.

• It uses technologies like RMI (Remote Method Invocation) and sockets for network communication.

• iii) Secure:

• Java provides a secure environment to run code, especially from untrusted sources.

• It uses a bytecode verifier to check code safety before running.

• The sandbox limits what the program can do to protect the system.

• Extra Points:

• Java was designed with the Internet in mind.

• Its features make it popular for network and web applications.

• Security and portability help Java programs run safely anywhere

• Question:

• Summarize different access controls in Java. Explain the situation if you remove the static modifier
from the main method.

•
• Answer 1: In Simple English

•
• Different Access Controls in Java:

• Java provides four types of access modifiers to control visibility of classes, methods, and variables:

• public

• Accessible from anywhere (all classes and packages).

• private

• Accessible only within the same class.

• protected

• Accessible within the same package and subclasses (even in different packages).

• default (no modifier)

• Accessible only within the same package (also called package-private).

• What happens if you remove static from main method?

• The main method must be static because Java calls it without creating an object.

• If static is removed, the JVM will not find the main method to start the program.

• This causes a runtime error: NoSuchMethodError: main.

• Extra Points:

• static means the method belongs to the class, not to an object.

• Access modifiers help in data hiding and security.

• Question:

• Write a program to print the area of a circle using a class Area. It should have:

• Method setRadius(double r) to set the radius.

• Method getArea() to return the area.

• Radius should be taken from the keyboard.

• Simple Java Program for Better Understanding

• java

• CopyEdit

• import java.util.Scanner;

• class Area {
• double r; // radius

• void setRadius(double x) {

• r = x;

• }

• double getArea() {

• return 3.14 * r * r; // πr²

• }

• }

• public class Main {

• public static void main(String[] args) {

• Scanner sc = new Scanner(System.in); // For input

• Area a = new Area(); // Create object

• System.out.print("Enter radius: ");

• double input = sc.nextDouble(); // Take input

• a.setRadius(input); // Set radius

• double result = a.getArea(); // Get area

• System.out.println("Area is: " + result); // Print result

• }

• }

• Explanation in Simple English

• Area class has one variable r to store radius.

• setRadius() method sets the radius.

• getArea() method returns area using formula πr².

• In main() method:
• User inputs radius.

• We use object a of Area class to set and get area.

• Final result is printed.

• Question:

• Explain the Garbage Collection concept in Java Programming with code example.

• Answer 1: In Simple English with Code Example

• What is Garbage Collection in Java?

• In Java, Garbage Collection (GC) is the process of automatically deleting unused (unreferenced)
objects from memory.

• Java has no delete keyword like C/C++.

• Garbage Collector runs in the background and frees memory used by objects that are no longer
needed.

• Why Garbage Collection is Important?

• Frees memory → avoids memory leaks

• Improves performance

• Programmer doesn't need to manually manage memory

• When is Object Eligible for GC?

• When there is no reference to the object

• Example:

• java

• CopyEdit

• Student s = new Student(); // object created

• s = null; // now it becomes eligible for GC

• Java Code Example:

• java

• CopyEdit
• class Test {

• // This method is called before object is deleted

• protected void finalize() {

• System.out.println("Object destroyed by Garbage Collector");

• }

• }

• public class Main {

• public static void main(String[] args) {

• Test t1 = new Test();

• Test t2 = new Test();

• t1 = null; // eligible for GC

• t2 = null; // eligible for GC

• System.gc(); // Request JVM to run garbage collector

• }

• }

• Output (May vary):

• vbnet

• CopyEdit

• Object destroyed by Garbage Collector

• Object destroyed by Garbage Collector

• Extra Points to Write in Exam:

• finalize() method is called before object is deleted by GC.

• System.gc() is used to request garbage collection (but JVM may ignore it).

• Helps in automatic memory management.

• Question:

• Explain command line arguments and variable length arguments in Java with an example.
•

• Answer 1: In Simple English + Code

• 1. Command Line Arguments in Java

• Command line arguments are values passed to the main() method when the Java program is run from
the terminal.

• These values are received as a String[] args array in main().

• Example:

• java

• CopyEdit

• public class CommandLine {

• public static void main(String[] args) {

• System.out.println("Command line arguments are:");

• for (int i = 0; i < args.length; i++) {

• System.out.println("Argument " + i + ": " + args[i]);

• }

• }

• }

• How to Run:

• bash

• CopyEdit

• javac CommandLine.java

• java CommandLine Hello 123 Java

• Output:

• yaml

• CopyEdit

• Command line arguments are:

• Argument 0: Hello

• Argument 1: 123

• Argument 2: Java

•
• 2. Variable Length Arguments (Varargs)

• Sometimes we don't know how many arguments we need.

• Java allows variable number of arguments using ... (three dots).

• Syntax:

• java

• CopyEdit

• void myMethod(int... numbers)

• Example:

• java

• CopyEdit

• public class VarArgsExample {

• static void display(String... names) {

• for (String name : names) {

• System.out.println("Name: " + name);

• }

• }

• public static void main(String[] args) {

• display("Amit", "Rahul");

• display("Sneha", "Neha", "Meena");

• }

• }

• Output:

• makefile

• CopyEdit

• Name: Amit

• Name: Rahul

• Name: Sneha

• Name: Neha

• Name: Meena

•
 • Extra Points for Exam:

• args[] is used to receive command line inputs.

• ... (three dots) is used to define variable number of arguments.

• You can pass 0 or more values using varargs.

• Varargs must always be the last parameter in method.

Question:

Write a program in Java using switch-case statement to perform Addition, Subtraction,

Multiplication, and Division of given two numbers and print the result.

Answer 1: In Simple English + Code

java
CopyEdit
import java.util.Scanner;

public class Calculator {

public static void main(String[] args) {
Scanner sc = new Scanner(System.in);

// Take input from user

System.out.print("Enter first number: ");
int a = sc.nextInt();

System.out.print("Enter second number: ");

int b = sc.nextInt();

System.out.println("Choose operation: ");

System.out.println("1 = Addition");
System.out.println("2 = Subtraction");
System.out.println("3 = Multiplication");
System.out.println("4 = Division");
int choice = sc.nextInt();

switch (choice) {
case 1:
System.out.println("Addition = " + (a + b));
break;
case 2:
System.out.println("Subtraction = " + (a - b));
break;
case 3:
System.out.println("Multiplication = " + (a * b));
break;
case 4:
if (b != 0) {
System.out.println("Division = " + (a / b));
} else {
System.out.println("Cannot divide by zero!");
}
 break;
default:
System.out.println("Invalid choice!");
}
}
}

Output Example:
yaml
CopyEdit
Enter first number: 10
Enter second number: 5
Choose operation:
1 = Addition
2 = Subtraction
3 = Multiplication
4 = Division
3
Multiplication = 50

Extra Points for Exam (Theory):

• switch-case is used to perform different operations based on user choice.
• Each case checks for a specific operation:
o 1: Addition (+)
o 2: Subtraction (-)
o 3: Multiplication (*)
o 4: Division (/)
• default is used if input is not 1-4.
• break is used to stop after one case is executed.
• Always check for division by zero to avoid errors.

Question:

Write a program which receives n integers, stores them in an array, and prints how many are odd and even.

Answer 1: In Simple English + Code

java

CopyEdit

import java.util.Scanner;

public class CountEvenOdd {

public static void main(String[] args) {

 Scanner sc = new Scanner(System.in);

// Take size of array

System.out.print("Enter how many numbers: ");

int n = sc.nextInt();

int[] arr = new int[n];

int even = 0, odd = 0;

// Take input numbers

System.out.println("Enter " + n + " numbers:");

for (int i = 0; i < n; i++) {

arr[i] = sc.nextInt();

// Check even or odd

if (arr[i] % 2 == 0)

even++;

else

odd++;

// Display results

System.out.println("Total Even numbers: " + even);

System.out.println("Total Odd numbers: " + odd);

Sample Output:

yaml

CopyEdit

Enter how many numbers: 5

Enter 5 numbers:

Total Even numbers: 2

Total Odd numbers: 3

Extra Theory Points (Simple for Exam):

• Array is used to store n numbers.

• Loop is used to read numbers and check if number is even (num % 2 == 0) or odd.

• Two counters: even and odd to keep count.

• Simple logic using % operator.