1. What is JVM, JRE, and JDK?
o JVM (Java Virtual Machine): It is a runtime environment that converts Java bytecode
into machine code.
o JRE (Java Runtime Environment): It contains the JVM and libraries to run Java
programs.
o JDK (Java Development Kit): It includes the JRE, compiler, and development tools
required for writing Java programs.
2. Define a class in Java with syntax and example.
o Definition: A class in Java is a blueprint for creating objects. It contains variables
(fields) and methods (functions).
o Syntax:
o class ClassName {
o // Variables
o // Methods
o }
o Example:
o class Car {
o String brand;
o void display() {
o System.out.println("Brand: " + brand);
o }
o }
3. What is the use of constructors in Java?
o Definition: A constructor is a special method used to initialize objects. It is called
automatically when an object is created.
o Syntax:
o class ClassName {
o ClassName() {
o // Constructor body
o }
o }
o Example:
o class Car {
o String brand;
o Car() { // Constructor
o brand = "Toyota";
o }
o }
4. List the different access specifiers in Java.
o Definition: Access specifiers control the visibility of classes, methods, and variables.
o Types:
private: Accessible only within the class.
default: Accessible within the same package.
protected: Accessible within the same package and subclasses.
public: Accessible from anywhere.
5. What is a static method? How is it different from an instance method?
o Definition: A static method belongs to the class and can be called without creating
an object.
o Syntax:
o class ClassName {
o static void methodName() {
o // Static method body
o }
o }
o Example:
o class MathUtils {
o static int square(int x) {
o return x * x;
o }
o }
o Difference: Instance methods require an object to be called, while static methods do
not.
Here are the remaining answers in the same format:
6. What is the purpose of JavaDoc comments?
o Definition: JavaDoc comments are special comments used to generate
documentation for Java classes, methods, and fields.
o Syntax:
o /**
o * This is a JavaDoc comment.
o * @param parameter_name Description
o * @return Description
o */
o Example:
o /**
o * This class represents a Car.
o */
o class Car {
o /**
o * Displays the car brand.
o */
o void display() {
o System.out.println("Car Brand");
o }
o }
7. What is a JavaBean? Mention its properties.
o Definition: A JavaBean is a reusable software component that follows certain
conventions.
o Properties of JavaBeans:
Must have a public no-argument constructor.
Must provide getter and setter methods for accessing private variables.
Must implement Serializable interface (optional).
o Syntax & Example:
o import java.io.Serializable;
o public class Car implements Serializable {
o private String brand;
o public Car() {} // No-arg constructor
o public String getBrand() {
o return brand;
o }
o public void setBrand(String brand) {
o this.brand = brand;
o }
o }
8. Define wrapper classes and give an example.
o Definition: Wrapper classes provide object representation for primitive data types.
o Syntax:
o WrapperClass obj = new WrapperClass(value);
o Example:
o Integer num = Integer.valueOf(10); // Wrapper class for int
9. What is the difference between StringBuilder and StringBuffer?
o StringBuffer: Thread-safe and synchronized (used in multi-threading).
o StringBuilder: Faster but not synchronized (used in single-threaded applications).
o Example:
o StringBuffer sbf = new StringBuffer("Hello");
o sbf.append(" World"); // Safe for multi-threading
o StringBuilder sbd = new StringBuilder("Hello");
o sbd.append(" World"); // Faster but not thread-safe
10. How does the switch statement work in Java?
Definition: The switch statement allows selecting a block of code from multiple options.
Syntax:
switch(expression) {
case value1:
// Code block
break;
case value2:
// Code block
break;
default:
// Default block
}
Example:
int day = 2;
switch(day) {
case 1: System.out.println("Monday"); break;
case 2: System.out.println("Tuesday"); break;
default: System.out.println("Invalid day");
}
11. What is the difference between break and continue statements?
break: Exits the loop completely.
continue: Skips the current iteration and moves to the next.
Example:
for(int i = 1; i <= 5; i++) {
if(i == 3) continue; // Skips 3
System.out.println(i);
}
12. Explain the difference between primitive and reference data types.
Primitive data types: Directly store values (e.g., int, char, double).
Reference data types: Store memory addresses (e.g., objects, arrays).
Example:
int a = 10; // Primitive
String str = "Hello"; // Reference
13. What are the different types of loops in Java?
for loop: Used for a fixed number of iterations.
while loop: Runs while a condition is true.
do-while loop: Runs at least once, then checks the condition.
Example:
for(int i = 0; i < 5; i++) {
System.out.println(i);
}
14. Define instance control flow in Java.
Definition: Instance control flow determines the execution order of instance variables and
blocks before the constructor.
Example:
class Test {
int x = 10;
{ // Instance block
System.out.println("Instance Block");
}
Test() {
System.out.println("Constructor");
}
public static void main(String[] args) {
Test obj = new Test();
}
}
Output:
Instance Block
Constructor
15. What is meant by regular expressions (RegEx) in Java?
Definition: Regular expressions are patterns used for text matching and searching.
Example:
import java.util.regex.*;
public class RegexExample {
public static void main(String[] args) {
Pattern p = Pattern.compile("\\d+"); // Matches digits
Matcher m = p.matcher("123ABC");
System.out.println(m.find()); // true
}
}
16. How is final different from static in Java?
final: Used to declare constants, prevent method overriding, and inheritance.
static: Used for class-level methods and variables.
Example:
class Example {
final int MAX = 100; // Constant value
static int count = 0; // Shared variable
}
