Java Interview Questions for Freshers with Clear & Concise Answers

Java is a programming language that was first introduced in 1995 by James Gosling and his team at Sun Microsystems. It is a high-level language that is easy to learn and write, making it one of the most popular programming languages in the world.

Java has a wide range of applications, including web development, desktop application development, and mobile app development. In India, Java is widely used in the software industry and there is a significant demand for skilled Java developers.

Freshers looking for a job in the software industry should have a good understanding of Java and its concepts. In this blog, we will outline 50 Java interview questions and answers for freshers commonly asked in job interviews. These questions cover concepts like object-oriented programming, data types, control structures, and exception handling. Let’s get started:

Java Interview Questions for Freshers

Let’s look into some of the basic questions asked in Java interview from freshers:

1. What is Java?

Java is a high-level, object-oriented programming language that was developed by Sun Microsystems in 1995. It is platform-neutral bytecode executed by the Java Virtual Machine (JVM), giving it the famous “write once, run anywhere” promise. Visit Oracle’s official website to download JVM.

2. Why is Java platform independent?

javac compiles source files into .class bytecode. Because every OS with a JVM can interpret that bytecode, the same binary runs unchanged across Windows, macOS, Linux, and even Android

3. What is JVM?

JVM stands for Java Virtual Machine. It is an abstract machine that provides the runtime environment in which Java programs are executed. The JVM interprets Java bytecode and translates it into machine-specific code.

4. What is the difference between JDK, JRE, and JVM?

JDK stands for Java Development Kit. It is a software development kit that includes tools for developing, compiling, and debugging Java programs. JRE stands for Java Runtime Environment. It is a software environment that provides the necessary runtime libraries and components for running Java programs. JVM is the virtual machine that executes the Java bytecode.

5. What is the difference between a class and an object?

A class is a blueprint or template for creating objects, while an object is an instance of a class. In other words, a class defines the properties and behaviors of an object, while an object is an instance of those properties and behaviors.

class Car { String model; }  
Car tesla = new Car();       // object

6. What is object-oriented programming?

Object-oriented programming (OOP) is a programming paradigm that is based on the concept of objects. In OOP, programs are organized around objects, which have properties (attributes) and behaviors (methods). OOP emphasizes encapsulation, inheritance, polymorphism, and abstraction.

7. What are default and static methods in interfaces?

From Java 8 onwards, interfaces can contain default methods (with a body) and static methods.

• Default methods allow you to add new methods to interfaces without breaking the classes that already implement them. They can be overridden in implementing classes.
• Static methods in interfaces belong to the interface itself, not to the implementing class. They can be called using InterfaceName.methodName().

8. What is inheritance?

Inheritance is a mechanism in which one class inherits properties and methods from another class. The class that inherits is called the subclass or derived class, and the class that is inherited from is called the superclass or base class.

class Animal { void sound(){} }  
class Dog extends Animal { void sound(){ System.out.println("Bark"); } }  

9. What is encapsulation?

Encapsulation is a mechanism in which data and methods are combined into a single unit called a class. Encapsulation provides data hiding, which means that the internal implementation details of a class are hidden from the outside world.

class Account {  
  private double balance;  
  public double getBalance(){ return balance; }  
}

10. What is polymorphism?

Polymorphism is a mechanism in which a single method can have different forms or implementations. Polymorphism can be achieved through method overloading or method overriding.

11. What is the Optional class and why is it used?

Optional<T> is a container object introduced in Java 8 that may or may not hold a non-null value.

• It’s used to avoid NullPointerException by explicitly handling cases where a value might be absent.
• Methods like isPresent(), orElse(), and ifPresent() make code safer and more expressive when dealing with potential nulls.

12. What are access modifiers?

Access modifiers are keywords that are used to specify the accessibility of a class, method, or variable. There are four types of access modifiers in Java: public, private, protected, and default.

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13. What are static variables and methods?

Static variables and methods belong to the class rather than to an instance of the class. This means that they can be accessed without creating an object of the class.

14. What are the final variables and methods?

Final variables and methods cannot be modified or overridden once they are defined. Final variables are constants, while final methods cannot be overridden by subclasses.

final variable = constant, method = cannot override, class = cannot extend.

15. What is a constructor?

A constructor is a special method that is used to initialize objects. It has the same name as the class and does not have a return type.

class Point { int x,y;  
  Point(){ this(0,0);}            // no-arg  
  Point(int x,int y){ this.x=x; this.y=y; }  // parameterised  
}

16. What are lambda expressions?

A lambda expression is a concise way to represent an anonymous function (function without a name).
Syntax: (parameters) -> expression or (parameters) -> { body }
Example:

List<String> names = Arrays.asList("A", "B", "C");
names.forEach(n -> System.out.println(n));

They make code shorter and are heavily used with functional interfaces, streams, and collections.

17. What is an array?

An array is a collection of elements of the same data type. It can be used to store data in a more organized and efficient way.

int[] nums = {1,2,3};

18. What are control structures in Java?

Control structures are statements that are used to control the flow of a program. They include if-else statements, switch statements, loops (for, while, do-while), and break and continue statements.

19. What is exception handling?

Exception handling is a mechanism in which errors or exceptions that occur during the program execution are caught and handled gracefully. It involves using try-catch blocks to catch exceptions and handle them appropriately.

Further Java Interview questions will test your Logical as well

20. What are the different types of exceptions in Java?

There are two types of exceptions in Java: checked exceptions and unchecked exceptions. Checked exceptions are checked at compile time, while unchecked exceptions are checked at runtime. Examples of checked exceptions include IOException and ClassNotFoundException, while examples of unchecked exceptions include NullPointerException and ArrayIndexOutOfBoundsException.

21. What is the difference between a HashSet and a TreeSet?

A HashSet is an unordered collection of unique elements, while a TreeSet is a sorted collection of unique elements.

22. What is the role of the ClassLoader in Java?

A ClassLoader is part of the JVM that loads Java classes into memory at runtime.

• Types: Bootstrap ClassLoader, Extension ClassLoader, and Application ClassLoader.
• It allows classes to be loaded dynamically, making Java platform-independent.
• Developers can also write custom class loaders for special use cases (like loading classes from a network or encrypted files).

23. What is the difference between shallow copy and deep copy?

• Shallow copy: Copies the object’s fields, but if the field is a reference (like an array or another object), only the reference is copied—not the actual data. Changes in the referenced object affect both copies.
• Deep copy: Creates a completely independent copy of the object and all the objects it references. Changes in one object don’t affect the other.

24. What is type erasure in Java generics?

Java implements generics through type erasure. This means that all generic type information is removed at compile time, and replaced with raw types or bounds.

For example, List<String> and List<Integer> Both become just List at runtime.
This ensures backward compatibility but also means generics cannot be used with primitives or checked at runtime.

25. What is the difference between a String, StringBuilder, and StringBuffer in Java?

A String is immutable, while a StringBuilder and StringBuffer are mutable. StringBuilder is not thread-safe, while StringBuffer is thread-safe.

26. What is a binary search tree? How can you implement one in Java?

A binary search tree is a data structure in which each node has at most two children, and the left child is smaller than the parent while the right child is larger. You can implement one in Java using recursion and comparison operators.

27. What is the difference between an abstract class and an interface in Java?

An abstract class is a class that cannot be instantiated and can contain abstract methods, while an interface is a collection of abstract methods and constants that can be implemented by any class.

28. How does garbage collection work in Java?

Java uses an automatic garbage collector (GC) to manage memory.

• Objects are allocated on the heap.
• When no live references point to an object, it becomes eligible for garbage collection.
• GC periodically reclaims this memory so the programmer doesn’t need to explicitly free it (like in C/C++).
  Methods like System.gc() can request GC, but the JVM decides the actual timing.

29. How do you implement a merge sort algorithm in Java?

You can implement a merge sort algorithm in Java using recursion and a merge method to combine two sorted arrays.

30. Provide an example of Polymorphism.

Polymorphism in Java refers to the ability of objects of different classes to be treated as if they are of the same class. An example is a superclass Animal with a method makeSound() that is overridden by subclasses Dog and Cat.

void log(int x){}              // overload  
void log(String s){}  
@Override  
void toString(){}              // override  

31. What is a daemon thread?

A daemon thread is a low-priority thread that runs in the background to support other threads.

• Examples: garbage collector, finalizer.
• The JVM exits when all user threads finish, regardless of whether daemon threads are still running.
  You can mark a thread as daemon using setDaemon(true) before starting it.

32. What is the difference between a private and a protected method in Java?

A private method is only accessible within the same class, while a protected method is accessible within the same class and any subclass.

33. How do you implement a bubble sort algorithm in Java?

You can implement a bubble sort algorithm in Java by iterating through the array and swapping adjacent elements if they are in the wrong order.

void bubble(int[] a){  
  for(int i=0;i<a.length-1;i++)  
    for(int j=0;j<a.length-i-1;j++)  
      if(a[j]>a[j+1]){ int t=a[j]; a[j]=a[j+1]; a[j+1]=t; }
}

34. What is the difference between a while loop and a do-while loop in Java?

A while loop executes the loop body if the condition is true, while a do-while loop executes the loop body at least once before checking the condition.

35. How do you implement a binary search algorithm in Java?

You can implement a binary search algorithm in Java by recursively dividing the search interval in half until the target element is found.

int binSearch(int[] a,int key){  
  int l=0,r=a.length-1;  
  while(l<=r){  
    int m=(l+r)/2;  
    if(a[m]==key) return m;  
    if(a[m]<key) l=m+1; else r=m-1;  
  }  
  return -1;  
}

36. What is a thread in Java? Provide an example of how to create a thread.

A thread in Java is a lightweight process that can execute independently of other threads. An example of creating a thread is extending the Thread class or implementing the Runnable interface and calling the start() method.

class MyJob implements Runnable {  
  public void run(){ System.out.println("Work"); }  
}
new Thread(new MyJob()).start();

37. What is the difference between a static and non-static variable in Java?

A static variable is associated with the class, while a non-static variable is associated with an instance of the class.

38. What is a deadlock in Java? How can you prevent it?

A deadlock in Java occurs when two or more threads are blocked waiting for each other to release resources. You can prevent it by avoiding circular dependencies and using thread-safe synchronization.

39. Explain marker interfaces vs functional interfaces.

• Marker interface: An interface with no methods or fields. It’s used as a tag for special behavior. Example: Serializable, Cloneable.
• Functional interface: An interface with exactly one abstract method. They are the foundation for lambda expressions. Example: Runnable, Callable, Comparator.

40. How do you implement a quick sort algorithm in Java?

You can implement a quick sort algorithm in Java using recursion and a partition method to divide the array into two parts.

void quick(int[] a,int low,int high){  
  if(low<high){  
    int p = partition(a, low, high);  
    quick(a, low, p-1);  
    quick(a, p+1, high);  
  }  
}

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Scenario-Based and Practical Java Interview Questions

41. You are building a login feature. How will you store user passwords securely in Java?

Passwords must never be stored in plain text. Use a hashing algorithm like PBKDF2, BCrypt, or Argon2 to convert the password into a fixed-length hash. Store only the hash in the database. At login, hash the input password and compare it with the stored hash.

import org.mindrot.jbcrypt.BCrypt;

String hashed = BCrypt.hashpw(password, BCrypt.gensalt());

boolean match = BCrypt.checkpw(inputPassword, hashed);

This approach protects users even if the database is leaked.

42. You notice your program creates too many objects and memory usage is high. How will you handle this?

Review the code and identify classes that can share data through the Flyweight pattern or reuse objects through object pooling. Reuse immutable objects like String where possible. Profile memory using tools like VisualVM to locate memory leaks. Apply WeakReference for objects that can be garbage collected when memory is low.

43. Your program needs to sort millions of records quickly. Which sorting approach will you use?

Use Merge Sort or Quick Sort from the Arrays.sort() method because they are optimized in Java. For primitive types, Java uses Dual-Pivot Quick Sort which is fast for large datasets.

int[] numbers = {5, 3, 1, 4, 2};

Arrays.sort(numbers);

This method is efficient and well-tested for production use.

44. A program must handle multiple users uploading files at the same time. How will you make it thread-safe?

Use synchronized blocks or locks to prevent two threads from writing to the same file simultaneously. Choose a thread-safe data structure like ConcurrentHashMap for shared data. Use ExecutorService to manage threads efficiently.

ExecutorService pool = Executors.newFixedThreadPool(10);

pool.submit(() -> uploadFile(userFile));

This improves performance and avoids data corruption.

45. Your REST API must return data quickly, but database queries are slow. How will you improve performance?

Introduce caching for frequently accessed data using libraries like Ehcache or Caffeine. Store results in memory for a short duration to reduce load on the database. Use connection pooling with HikariCP to speed up database access.

46. You receive a list of email addresses and need to validate them. How will you do it in Java?

Use regular expressions with Pattern and Matcher classes. Compile the pattern once and reuse it for multiple inputs.

Pattern pattern = Pattern.compile(“^[A-Za-z0-9+_.-]+@[A-Za-z0-9.-]+$”);

Matcher matcher = pattern.matcher(email);

if(matcher.matches()) {

    System.out.println(“Valid email”);

}

This avoids invalid data entering the system.

47. A program must read a very large file line by line without consuming too much memory. What is the solution?

Use BufferedReader which reads data efficiently and keeps memory usage low.

try(BufferedReader reader = new BufferedReader(new FileReader(“data.txt”))) {

    String line;

    while((line = reader.readLine()) != null) {

        process(line);

    }

}

This is efficient because only one line is loaded into memory at a time.

48. A team reports that your API crashes when it receives null values. How will you handle it?

Use the Optional class to represent values that may be absent. Replace direct null checks with isPresent() and orElse() for better readability.

Optional<String> value = Optional.ofNullable(input);

String result = value.orElse(“default”);

This makes the code safer and prevents NullPointerException.

49. You must share data across different parts of a program, but global variables create conflicts. What will you do?

Create a Singleton class that holds shared data. Make the constructor private and expose a getInstance() method to control access.

public class Config {

    private static Config instance;

    private Config() {}

    public static synchronized Config getInstance() {

        if(instance == null) {

            instance = new Config();

        }

        return instance;

    }

}

This gives a single source of truth across the application.

50. Your system processes payments and must not process the same transaction twice. How will you guarantee this?

Generate a unique transaction ID and store it in a database table with a unique constraint. Before processing a payment, check if the transaction ID already exists. Use database-level locking or optimistic concurrency to avoid duplicates under high load.

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Conclusion

You now have 50 carefully selected Java interview questions that cover both theory and real-world application. The first 40 questions strengthen your understanding of fundamental concepts like OOP, collections, exception handling, and memory management. The 10 scenario-based questions help you think through real programming challenges that reflect the problems developers solve every day.

Practice every question until you can explain the concept and write the code confidently. Test your solutions with multiple inputs and refine them until they work perfectly. Build small projects that combine classes, interfaces, multithreading, and data handling to develop a deeper understanding of how Java works in practice.

Interviews reward candidates who communicate their thought process clearly. Explain why you chose a particular solution, describe possible improvements, and show that you can adapt if the interviewer changes the requirements. This demonstrates technical skill as well as problem-solving ability.

With these 50 interview questions and answers, you now have a focused roadmap to prepare for your Java interview. Consistent practice will strengthen your skills and give you the confidence to perform under pressure. Treat each question as an opportunity to grow as a developer and take one step closer to starting a successful career in software development.

FAQs on Java Interview Questions & Answers for Freshers

Q1. What are the questions asked in a Java interview for freshers?

Most Asked Java Interview Questions
What is Java?
Why is Java a platform-independent language?
What are the differences between C++ and Java?
Why is Java not a pure object-oriented language?

Q2. How to clear a Java interview?

You must have a clear understanding of the basic concepts like:

Java Fundamentals.
Data Structure and Algorithms.
Object-Oriented Concepts.
Multithreading, concurrency, and thread basics.
Java Collections Framework.
Date type conversion and fundamentals.
Array.
Garbage Collection.

Q3. Is Java good for freshers?

As a fresher, both Java and Python are excellent choices for learning programming and starting a career in software development