Java plays a big role in the current tech industry. It is a versatile programming language widely used for building applications, from web services to mobile apps. Java’s object-oriented nature allows developers to create modular programs, making it easier to manage and scale projects.
Professionals working with Java should be familiar with data structures, algorithms, and core concepts of the language such as class, inheritance, and polymorphism. Java professionals are expected to know object-oriented programming (OOP), Java frameworks like Spring or Hibernate, databases, APIs, multithreading, exception handling, and sometimes real-time problem-solving using Java code.
Preparing for a Java interview is very important because it’s not just about understanding theory, you also need to show practical skills, explain concepts clearly, and solve coding challenges or real-life problems using Java. Good preparation helps you feel confident, answer technical questions smoothly, and stand out from other candidates.
Here, we are sharing many popular Java interview questions and answers, from fresher to experienced candidates. We will provide a PDF download so you can also prepare offline.
Table of Contents
Top Java interview Questions and Answers for Freshers
First, we will share popular basic java interview questions and answers, focusing on fresh candidates preparing for java roles.
1. What are the main features of Java?
Answer:
- Object-Oriented
- Platform Independent
- Secure
- Robust
- Multithreaded
- High Performance (via JVM and JIT compiler)
2. What is the difference between JDK, JRE, and JVM?
Answer:
| Component | Description |
|---|---|
| JDK | Java Development Kit – includes tools and compiler |
| JRE | Java Runtime Environment – provides libraries and JVM |
| JVM | Java Virtual Machine – runs Java bytecode |
3. What are primitive data types in Java?
Answer:
- byte
- short
- int
- long
- float
- double
- char
- boolean
4. What is the difference between == and .Equals() in Java?
Answer:
- == checks reference (memory address) equality
- .equals() checks logical value equality (can be overridden in classes)
Example:
String a = new String("Test");
String b = new String("Test");
System.out.println(a == b); // false
System.out.println(a.equals(b)); // true5. What is method overloading?
Answer:
Method overloading means defining multiple methods with the same name but different parameters in the same class.
Example:
void print(int a) {}
void print(String a) {}6. What is method overriding?
Answer:
Method overriding occurs when a subclass provides a specific implementation of a method already defined in its superclass.
class Animal {
void sound() { System.out.println("Animal sound"); }
}
class Dog extends Animal {
void sound() { System.out.println("Bark"); }
}7. What is the purpose of the Final keyword?
Answer:
- final variable: cannot be changed
- final method: cannot be overridden
- final class: cannot be extended
8. What is inheritance in Java?
Answer:
Inheritance allows one class to inherit properties and methods from another class using the extends keyword.
class Parent {}
class Child extends Parent {}9. What is polymorphism?
Answer:
Polymorphism allows methods to perform different behaviors based on the object. It includes method overloading and overriding.
10. What is an interface in Java?
Answer:
An interface is a contract that contains method signatures without implementations.
interface Animal {
void sound();
}A class can implement an interface using the implements keyword.
11. What is the difference between abstract class and interface?
Answer:
| Abstract Class | Interface |
|---|---|
| Can have method body | Only method signatures (Java 7) |
| Can have constructors | Cannot have constructors |
| Supports multiple inheritance via interfaces | Supports multiple inheritance |
12. What is a constructor?
Answer:
A constructor is a special method used to initialize objects. It has the same name as the class and no return type.
class Car {
Car() { System.out.println("Car created"); }
}13. What is the difference between ArrayList and LinkedList?
Answer:
| ArrayList | LinkedList |
|---|---|
| Fast for random access | Fast for insert/delete |
| Backed by array | Backed by nodes |
| Uses more memory efficiently | Requires more memory |
14. What is exception handling in Java?
Answer:
Exception handling allows the program to continue running even after encountering an error using try, catch, finally, and throw.
try {
int a = 5 / 0;
} catch (ArithmeticException e) {
System.out.println("Cannot divide by zero");
}15. What is the difference between “checked” and “unchecked” exceptions?
Answer:
- Checked exceptions: must be handled using try-catch or declared with throws (e.g., IOException)
- Unchecked exceptions: runtime errors (e.g., NullPointerException)
16. What are access modifiers in Java?
Answer:
- private: accessible within the class
- default (no modifier): accessible within the package
- protected: accessible within package and subclass
- public: accessible everywhere
17. What is the difference between String, StringBuilder, and StringBuffer?
Answer:
| Class | Thread-Safe | Mutable | Use Case |
|---|---|---|---|
| String | No | No | Constant values |
| StringBuilder | No | Yes | Faster in single-threaded |
| StringBuffer | Yes | Yes | Thread-safe needs |
18. What is garbage collection in Java?
Answer:
Garbage collection is the automatic process of removing unused objects from memory to free up resources. It is managed by the JVM.
19. What is multithreading in Java?
Answer:
Multithreading allows concurrent execution of two or more threads to maximize CPU usage.
class MyThread extends Thread {
public void run() {
System.out.println("Thread running");
}
}20. What is the use of the “This” keyword in Java?
Answer:
- Refers to the current class instance
- Used to avoid confusion between class variables and parameters
- Can be used to call other constructors in the same class
class Car {
String color;
Car(String color) {
this.color = color;
}
}
Core Java interview Questions and Answers for Experienced
We have already shared the basic Java interview questions, so now we are sharing advanced core Java interview questions for experienced candidates. These questions cover key Java concepts such as OOP, multithreading, memory, collections, and advanced programming techniques.
21. What is the difference between == and .equals() in Java?
Answer:
==compares object references.equals()compares values (if overridden)
String a = new String("Test");
String b = new String("Test");
System.out.println(a == b); // false
System.out.println(a.equals(b)); // true22. What is the use of “transient” keyword in Java?
Answer:
The transient keyword is used to prevent serialization of a variable.
transient int tempValue;
When an object is serialized, tempValue is skipped.
23. What is the difference between HashMap and ConcurrentHashMap?
Answer:
| Feature | HashMap | ConcurrentHashMap |
|---|---|---|
| Thread-safe | No | Yes |
| Allows null keys | One null key | No null key allowed |
| Performance | Faster (single-threaded) | Better in multi-threaded environments |
24. What is the difference between String, StringBuilder, and StringBuffer?
Answer:
| Class | Mutable | Thread-Safe | Use Case |
|---|---|---|---|
| String | No | Yes (immutable) | Fixed content |
| StringBuilder | Yes | No | Better performance (single thread) |
| StringBuffer | Yes | Yes | Use when thread safety needed |
25. What are wrapper classes in Java?
Answer:
Wrapper classes convert primitive data types into objects.
Examples:
int→Integerdouble→Doublechar→Character
26. How does Java handle memory management?
Answer:
- Managed by JVM
- Memory areas include heap, stack, method area
- Garbage collector reclaims memory of unused objects
- Developers can request GC with
System.gc()(but not guaranteed)
27. What is the difference between ArrayList and Vector?
Answer:
| Feature | ArrayList | Vector |
|---|---|---|
| Thread-Safe | No | Yes |
| Performance | Faster | Slower (synchronized) |
| Growth Policy | Increases 50% | Doubles in size |
28. What is method hiding in Java?
Answer:
Method hiding happens when a static method in a subclass has the same signature as in the parent class. It does not override but hides the superclass method.
29. What is the difference between final, finally, and finalize()?
Answer:
final: restricts inheritance or changesfinally: block always executed after try-catchfinalize(): called by GC before destroying object (deprecated)
30. What is the role of the “volatile” keyword?
Answer:
Ensures visibility of changes made by one thread to other threads. It prevents caching of variables.
31. What is the difference between Abstract Class and Interface in Java 8 and later?
Answer:
| Feature | Abstract Class | Interface (Java 8+) |
|---|---|---|
| Method Types | Abstract and concrete | Abstract, default, static |
| Multiple Inheritance | Not supported | Supported |
| Constructor | Allowed | Not allowed |
32. How do you handle thread deadlock in Java?
Answer:
- Avoid nested locks
- Use
tryLock()with timeout - Use lock ordering
- Detect using thread dumps and tools like VisualVM
33. What are functional interfaces?
Answer:
An interface with only one abstract method. Used in lambda expressions.
Example:
@FunctionalInterface
interface MyFunc {
void execute();
}34. What is the Stream API in Java?
Answer:
Introduced in Java 8 to process collections using a declarative style.
Example:
list.stream().filter(x -> x > 10).forEach(System.out::println);35. What is the difference between HashSet and TreeSet?
Answer:
| Feature | HashSet | TreeSet |
|---|---|---|
| Ordering | Unordered | Sorted (natural or comparator) |
| Performance | Faster (O(1)) | Slower (O(log n)) |
| Null | Allows one null | Does not allow null |
36. What is immutability and how can you create an immutable class?
Answer:
Immutable class cannot be changed once created.
Steps:
- Make class
final - Make fields
private final - No setters
- Initialize via constructor
- Return copies of mutable objects
37. How does Java support multi-threading?
Answer:
- By extending
Threador implementingRunnable - Java provides
ExecutorService,Callable,Futurefor advanced concurrency - Thread lifecycle: New, Runnable, Running, Blocked, Terminated
38. What is reflection in Java?
Answer:
Reflection allows inspection and modification of classes, fields, and methods at runtime.
Example:
Class<?> cls = Class.forName("MyClass");
Method m = cls.getMethod("myMethod");
m.invoke(obj);39. What are the types of class loaders in Java?
Answer:
- Bootstrap ClassLoader
- Extension ClassLoader
- System ClassLoader
- Custom ClassLoader (user-defined)
40. What are annotations in Java?
Answer:
Annotations provide metadata about the code. Common ones:
@Override@Deprecated@FunctionalInterface- Custom annotations can be created using
@interface
41. What is the difference between == and .equals() in Java? Explain with examples.
Answer:
==compares object references (memory addresses) for objects, and actual values for primitives.equals()compares the actual content/value of objects- String literals are stored in string pool, so
==might work for literals but not for new String objects - Custom classes should override
.equals()method for meaningful comparison
Example:
String s1 = "hello";
String s2 = "hello";
String s3 = new String("hello");
System.out.println(s1 == s2); // true (same reference in string pool)
System.out.println(s1 == s3); // false (different references)
System.out.println(s1.equals(s3)); // true (same content)42. Explain the concept of method overriding vs method overloading in Java.
Answer:
Method Overloading (Compile-time polymorphism):
- Same method name with different parameters (number, type, or order)
- Occurs within the same class
- Return type can be different but cannot be the only difference
- Resolved at compile time
Method Overriding (Runtime polymorphism):
- Child class provides specific implementation of parent class method
- Same method signature (name, parameters, return type)
- Uses
@Overrideannotation - Resolved at runtime based on actual object type
Example:
// Overloading
class Calculator {
public int add(int a, int b) { return a + b; }
public double add(double a, double b) { return a + b; }
}
// Overriding
class Animal {
public void makeSound() { System.out.println("Animal sound"); }
}
class Dog extends Animal {
@Override
public void makeSound() { System.out.println("Woof!"); }
}43. What are the key differences between ArrayList and LinkedList? When would you use each?
Answer:
ArrayList:
- Backed by dynamic array
- Fast random access O(1) using index
- Slower insertion/deletion in middle O(n) due to shifting
- Better for read-heavy operations
- Less memory overhead per element
LinkedList:
- Backed by doubly linked list
- Slow random access O(n) – must traverse from head/tail
- Fast insertion/deletion O(1) if you have reference to node
- Better for frequent insertions/deletions
- More memory overhead due to node pointers
Use Cases:
- ArrayList: When you need frequent random access, iteration, or size is relatively stable
- LinkedList: When you frequently insert/delete elements at beginning/middle, or implement queue/deque
Performance Comparison:
list.get(index); // O(1)
list.add(element); // O(1) amortized
list.add(index, elem); // O(n)
// LinkedList - good for
list.addFirst(element); // O(1)
list.removeFirst(); // O(1)
list.get(index); // O(n)Scenario-Based Java Multithreading Interview Questions
Now its time to take a look on Scenario Based Java Multithreading Interview Questions crafted for practical understanding. These questions gradually increase in difficulty and focus on real-world problem-solving, synchronization, concurrency utilities, and thread lifecycle management.
44. You have two threads printing numbers from 1 to 10. How do you ensure the threads take turns?
Answer:
Use synchronized blocks and a shared lock object with wait() and notify() to alternate between threads.
45. A shared counter is updated by multiple threads, but the final count is inconsistent. What would you do?
Answer:
Synchronize the method or use AtomicInteger to make the counter thread-safe.
AtomicInteger counter = new AtomicInteger(0);
counter.incrementAndGet();46. You want to stop a running thread on a button click. How do you do that safely?
Answer:
Use a volatile boolean flag to control thread execution.
volatile boolean running = true;
public void run() {
while (running) {
// work
}
}47. A thread must wait until another thread completes a task. Which approach do you use?
Answer:
Use Thread.join() or CountDownLatch.
Thread t = new Thread(task);
t.start();
t.join();48. How do you ensure only one thread can access a critical section in a high-load environment?
Answer:
Use ReentrantLock for finer control compared to synchronized.
Lock lock = new ReentrantLock();
lock.lock();
try {
// critical section
} finally {
lock.unlock();
}49. You have to process 10 tasks in parallel and then combine the results. How do you design it?
Answer:
Use ExecutorService with invokeAll() or CompletableFuture.allOf() to run tasks in parallel and wait for completion.
50. Your application is experiencing deadlock in production. How would you identify and fix it?
Answer:
- Use thread dump analysis
- Avoid nested locks or use consistent lock ordering
- Prefer
tryLock()with timeout to avoid blocking
51. How do you implement a producer-consumer scenario using Java’s concurrent utilities?
Answer:
Use BlockingQueue to decouple producers and consumers.
BlockingQueue<Integer> queue = new ArrayBlockingQueue<>(10);
queue.put(1); // producer
queue.take(); // consumer52. You need to schedule a task every 5 seconds. What Java feature do you use?
Answer:
Use ScheduledExecutorService.
ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
scheduler.scheduleAtFixedRate(task, 0, 5, TimeUnit.SECONDS);53. A method updates multiple shared resources. How do you avoid data inconsistency without blocking all threads?
Answer:
Use fine grained locking or StampedLock to lock only the necessary resources, allowing higher concurrency with data safety.
Java Automation Testing interview Questions and Answers
Next questions are focused on automation testing, progressing from foundational to moderately advanced concepts.
54. What are the benefits of using Java in automation testing?
Answer:
- Strong OOP support for reusable test components
- Rich ecosystem (Selenium, TestNG, JUnit, Maven)
- Robust exception handling
- Readability and maintainability
- Strong community support
55. How do you locate web elements using Selenium WebDriver in Java?
Answer:
Use methods like findElement() with locators such as:
driver.findElement(By.id("username"));
driver.findElement(By.xpath("//input[@name='email']"));
driver.findElement(By.cssSelector(".btn-primary"));56. How do you handle synchronization issues in Selenium?
Answer:
Use waits:
- Implicit Wait: Waits globally
- Explicit Wait: Waits for a specific condition
- Fluent Wait: Custom polling and exceptions
Example:
WebDriverWait wait = new WebDriverWait(driver, Duration.ofSeconds(10));
wait.until(ExpectedConditions.visibilityOfElementLocated(By.id("login")));57. What is the difference between Assert and Verify in test automation?
Answer:
| Feature | Assert | Verify |
|---|---|---|
| Stops execution on failure | Yes | No |
| Common in | JUnit/TestNG | Custom logging logic |
| Example | Assert.assertTrue(condition) | if(condition){ log success; } else { log failure; } |
58. What is a Page Object Model in Java automation testing?
Answer:
Page Object Model (POM) is a design pattern that creates separate classes for each page of the application. It helps:
- Improve maintainability
- Reduce code duplication
- Enhance readability
Example:
public class LoginPage {
WebDriver driver;
@FindBy(id="username") WebElement username;
@FindBy(id="password") WebElement password;
public void login(String user, String pass) {
username.sendKeys(user);
password.sendKeys(pass);
}
}59. How do you run your Selenium tests in parallel using Java?
Answer:
- Use TestNG with
parallel="tests"intestng.xml - Use
@DataProviderwithparallel=true - Use thread-safe WebDriver setup (ThreadLocal or WebDriverManager)
60. How do you handle file uploads in Selenium using Java?
Answer:
Use sendKeys() on file input elements.
WebElement upload = driver.findElement(By.id("file"));
upload.sendKeys("C:\\Users\\file.png");If native OS dialog is involved, use tools like Robot class or AutoIt.
61. What is the role of Maven in Java automation testing?
Answer:
- Dependency management
- Build automation
- Integration with TestNG, JUnit
- Organizes project with standard structure
Example pom.xml snippet:
<dependency>
<groupId>org.seleniumhq.selenium</groupId>
<artifactId>selenium-java</artifactId>
<version>4.0.0</version>
</dependency>62. How do you take a screenshot in Selenium using Java?
Answer:
Use TakesScreenshot interface.
File src = ((TakesScreenshot)driver).getScreenshotAs(OutputType.FILE);
FileUtils.copyFile(src, new File("screenshot.png"));63. How do you design a test automation framework in Java?
Answer:
Framework components may include:
- TestNG/JUnit for test execution
- POM for structure
- Utility classes for common actions
- Logging with Log4j or ExtentReports
- Data-Driven Testing using Excel, CSV, or DB
- Build tools like Maven or Gradle
- CI integration with Jenkins or GitHub Actions
Java Interview Questions PDF
We’ve shared various types of questions, and now we’re adding PDF file of that, so you can prepare offline without any ads distractions.
FAQs: Java interview
What is the role of a Java developer in a company?
A Java developer is responsible for designing, developing, and maintaining software applications using the Java programming language. Their role often includes writing clean code, debugging errors, working with databases, using frameworks like Spring or Hibernate, and collaborating with other developers to build scalable applications.
What types of challenges do candidates face during Java interviews?
Candidates often face challenges like answering complex coding questions under time pressure, solving real-life technical scenarios, explaining core concepts like OOP, multithreading, and exception handling, and demonstrating practical knowledge of Java frameworks. Interviews may also include live coding rounds and technical problem-solving tasks.
Why is Java still in demand in 2025?
Java remains in demand because it’s widely used in enterprise software, banking systems, Android development, cloud applications, and backend services. Its stability, scalability, and strong community support make it a preferred choice for many organizations, keeping the demand for skilled Java developers high.
What technical skills should candidates have for Java jobs?
Candidates should be skilled in Java programming, object-oriented programming (OOP), data structures, algorithms, working with databases (SQL), using frameworks like Spring Boot and Hibernate, REST APIs, and basic knowledge of version control systems like Git. Knowing software development principles like Agile or DevOps is often a plus.
What is the average salary for Java developers in the USA?
The average salary for a Java developer in the USA typically ranges from $80,000 to $130,000 per year, depending on experience level, location, and company size. Senior Java developers or those working in specialized industries may earn salaries above $150,000 annually.
Which top companies hire Java developers?
Many leading companies hire Java professionals regularly. These include Amazon, Google, Microsoft, IBM, Oracle, Accenture, TCS, Infosys, Cognizant, JPMorgan Chase, and Wipro, among others. Both startups and large enterprises look for skilled Java developers for various backend and full-stack roles.
How can preparing for Java interviews help in career growth?
Preparing for Java interviews improves your coding skills, deepens your understanding of core concepts, and boosts your confidence during technical discussions. Well-prepared candidates have better chances of getting hired by top companies, negotiating higher salaries, and progressing into senior or specialized Java development roles.
Conclusion
In the article above, we have shared a wide range of Java interview questions and answers, covering everything from basic questions for freshers to core Java questions for experienced candidates, along with real-world scenario-based questions to help you prepare better.
We have also provided a PDF, so you can easily study offline and prepare anytime at your convenience. Best wishes for your upcoming interview.
