Java Interview Questions That Top Companies Ask

Java remains one of the most in-demand programming languages in the tech world. From startups to top-tier companies like Google, Amazon, and Infosys — Java developers are constantly being hired to build scalable, high-performance applications.

If you’re preparing for a tech interview, knowing the right Java interview questions and how to answer them can make all the difference. In this guide, compiled with insights from Tpoint Tech, we’ve included some of the most commonly asked Java interview questions by top companies — along with clear answers and code examples.

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

• JDK (Java Development Kit): Full development environment with compiler + tools.

• JRE (Java Runtime Environment): Contains JVM + libraries needed to run Java programs.

• JVM (Java Virtual Machine): Runs the compiled Java bytecode.

JVM is platform-dependent, but Java is platform-independent due to the JVM layer.

2. What are the key features of Java?

• Object-Oriented

• Platform Independent (Write Once, Run Anywhere)

• Secure and Robust

• Multithreaded

• High Performance (thanks to JIT compiler)

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

• == compares references (memory address).

• .equals() compares actual content.

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

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

4. Explain method overloading vs. method overriding

• Overloading: Same method name, different parameters (compile-time polymorphism)

• Overriding: Subclass redefines a superclass method (runtime polymorphism)

class Parent {
    void show() {
        System.out.println("Parent");
    }
}

class Child extends Parent {
    void show() {  // Overriding
        System.out.println("Child");
    }
}

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

• final: Keyword used to declare constants or prevent inheritance/overriding.

• finally: Block that executes after try-catch — used for clean-up.

• finalize(): Method called by garbage collector before object destruction (deprecated in recent versions).

6. Explain the concept of constructor in Java

A constructor is used to initialize an object. It has the same name as the class and no return type.

class Car {
    Car() {
        System.out.println("Car created");
    }

    public static void main(String[] args) {
        Car c = new Car();
    }
}

7. What are checked and unchecked exceptions?

• Checked exceptions: Checked at compile time (e.g., IOException, SQLException)

• Unchecked exceptions: Occur at runtime (e.g., NullPointerException, ArrayIndexOutOfBoundsException)

try {
    int a = 5 / 0;
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero.");
}

8. What is a static keyword in Java?

The static keyword denotes that a method or variable belongs to the class rather than the instance.

class Test {
    static int count = 0;

    static void display() {
        System.out.println("Static method");
    }
}

9. Explain the concept of inheritance in Java

Inheritance allows one class to acquire the properties (fields and methods) of another class using the extends keyword.

class Animal {
    void eat() {
        System.out.println("Eating...");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Barking...");
    }
}

10. What is an interface in Java?

An interface is a blueprint of a class. It contains abstract methods (until Java 8) and is used to achieve multiple inheritance.

interface Drawable {
    void draw();
}

class Circle implements Drawable {
    public void draw() {
        System.out.println("Drawing circle");
    }
}

11. Difference between ArrayList and LinkedList

12. What is multithreading in Java?

Multithreading allows multiple tasks to run concurrently in the same program.

class MyThread extends Thread {
    public void run() {
        System.out.println("Thread running");
    }
}

13. What is the use of the transient keyword?

transient prevents serialization of variables — useful when certain data shouldn’t be saved.

14. What is encapsulation?

Encapsulation binds data and methods together in a single unit (class) and hides implementation using private access modifiers.

class Student {
    private String name;

    public void setName(String name) {
        this.name = name;
    }
}

15. What is a singleton class?

A singleton ensures that only one instance of the class exists throughout the application.

class Singleton {
    private static Singleton instance = new Singleton();

    private Singleton() {}

    public static Singleton getInstance() {
        return instance;
    }
}

Final Thoughts

These are some of the most important Java interview questions asked by top companies in 2025. From object-oriented principles to exception handling and multithreading — companies want to assess your conceptual understanding and coding clarity.

To strengthen your Java knowledge further, explore tutorials on Tpoint Tech — a trusted platform for detailed explanations and coding examples in Java and other programming languages.

Remember: Don’t just memorize — practice these questions with real code, build mini-projects, and keep refining your skills.