Java remains one of the most in-demand programming languages in the tech industry, even in 2025. With its versatility and wide adoption in enterprise, web, and mobile app development, mastering Java is essential for aspiring developers. Preparing for Java interviews can be daunting, but this blog will break down 10 commonly asked Java interview questions along with insightful answers to help you ace your next interview.So, whether you’re a fresher or an experienced developer, these questions will give you the edge you need to stand out. Let’s dive in!

Table of Contents

1. What is Java? Explain its key features.
2. What are the differences between JDK, JRE, and JVM?
3. Explain the concept of OOP in Java.
4. What is the difference between == and .equals() in Java?
5. What are Java access modifiers?
6. What is the difference between ArrayList and LinkedList in Java?
7. Explain Java’s garbage collection process.
8. What are checked and unchecked exceptions in Java?
9. What is the difference between final, finally, and finalize?
10. What is the significance of Java 17 (or later versions)?

1. What is Java? Explain its key features.

Java is a high-level, object-oriented programming language developed by Sun Microsystems (now owned by Oracle). It is platform-independent due to its Write Once, Run Anywhere (WORA) capability, which means Java code can run on any system equipped with a Java Virtual Machine (JVM).

Key Features of Java:

• Object-Oriented: Everything in Java is based on objects.
• Platform-Independent: Bytecode can run on any platform with a JVM.
• Robust: Strong memory management with garbage collection.
• Secure: Features like bytecode verification and runtime security.
• Multithreaded: Java supports concurrent programming.
• High Performance: With Just-In-Time (JIT) compilation, Java provides good performance.

2. What are the differences between JDK, JRE, and JVM?

This is a fundamental question that every Java programmer should know.

Diagram Suggestion:

Insert an image here showing the relationship between JDK, JRE, and JVM in layers.

3. Explain the concept of OOP in Java.

Java is an object-oriented programming (OOP) language. OOP is based on the following four principles:

1. Encapsulation: Wrapping data (variables) and methods into a single unit (class).
2. Inheritance: Acquiring properties and behaviors of a parent class in a child class.
3. Polymorphism: The ability to perform a single action in different ways (e.g., method overriding and overloading).
4. Abstraction: Hiding implementation details and exposing only the essential features.

Example Code:

class Animal {
    void sound() {
        System.out.println("This is a generic animal sound");
    }
}

class Dog extends Animal {
    @Override
    void sound() {
        System.out.println("Woof! Woof!");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal a = new Dog();
        a.sound(); // Outputs: Woof! Woof!
    }
}

4. What is the difference between == and .equals() in Java?

• == Operator: Compares references (memory locations) of objects.
• .equals() Method: Compares the actual content of objects for equality.

Example:

String s1 = new String("Java");
String s2 = new String("Java");

System.out.println(s1 == s2); // false (different memory locations)
System.out.println(s1.equals(s2)); // true (content is the same)

5. What are Java access modifiers?

Access modifiers in Java determine the visibility of a class, method, or variable. The four types are:

6. What is the difference between ArrayList and LinkedList in Java?

These two are part of the Java Collections Framework but have different implementations and use cases.

7. Explain Java’s garbage collection process.

Garbage collection in Java is an automatic process that reclaims memory occupied by objects that are no longer in use. It is managed by the JVM.

Phases of Garbage Collection:

1. Mark: Identifies objects that are still in use.
2. Sweep: Removes unreferenced objects.
3. Compact: Rearranges memory to eliminate fragmentation.

Example Code Triggering Garbage Collection:

class GarbageExample {
    public static void main(String[] args) {
        GarbageExample obj = new GarbageExample();
        obj = null; // Eligible for garbage collection
        System.gc(); // Request garbage collection
    }
    
    @Override
    protected void finalize() {
        System.out.println("Garbage collected!");
    }
}

8. What are checked and unchecked exceptions in Java?

• Checked Exceptions: Exceptions that are checked at compile time. Example: IOException.
• Unchecked Exceptions: Exceptions that occur at runtime. Example: ArithmeticException.

Example:

// Checked Exception
try {
    FileReader file = new FileReader("nonexistent.txt");
} catch (IOException e) {
    e.printStackTrace();
}

// Unchecked Exception
int result = 10 / 0; // Throws ArithmeticException

9. What is the difference between final, finally, and finalize?

This is a common question because these terms sound similar but serve different purposes.

10. What is the significance of Java 17 (or later versions)?

Java 17 is a long-term support (LTS) version that introduced several improvements to the language. If you’re preparing for interviews in 2025, it’s essential to know about recent updates.

Key Features of Java 17:

• Sealed Classes: Restrict which classes can extend or implement a class.
• Pattern Matching for switch: Simplifies complex switch cases.
• JEP 356: Enhanced JVM performance with better memory management.

Conclusion

Mastering these top 10 Java interview questions and understanding their answers will give you the confidence to tackle your next job interview. Remember, practice is key! Write code, experiment, and dive deep into these concepts. Java is a vast language, but with dedication and preparation, you’ll land your dream job in 2025.