Question 1

What is the purpose of the `public static void main` method?

Accepted Answer

The `public static void main` method is the entry point for any Java application. The JVM calls it to start execution, and it’s `public` so the JVM can access it, `static` so no object is needed, and `void` because it doesn’t return anything. Without it, your program won’t run!

Question 2

What is method overloading in Java?

Accepted Answer

Method overloading lets you define multiple methods with the same name but different parameter lists (type, number, or order). Java picks the right one based on the arguments you pass. It’s great for flexibility—like having one `print` method for ints and another for strings.

Question 3

What is the `static` keyword in Java?

Accepted Answer

The `static` keyword makes a member belong to the class itself, not instances. Static variables are shared across all objects, and static methods can be called without creating an object—like `Math.sqrt()`. It’s useful for utilities or counters but can complicate testing if overused.

Question 4

What does the `final` keyword do in Java?

Accepted Answer

The `final` keyword locks things down: a `final` variable can’t be reassigned, a `final` method can’t be overridden, and a `final` class can’t be subclassed. It’s perfect for constants or ensuring critical logic stays unchanged, like in a math utility class.

Question 5

What is the `System` class in Java?

Accepted Answer

The `System` class provides utility methods and fields, like `out` for console output, `currentTimeMillis()` for timing, and `exit()` to stop the JVM. It’s `final`, so you can’t subclass it—just a handy toolbox for system-level operations.

Question 6

What is the difference between `public`, `private`, and `protected`?

Accepted Answer

These are access modifiers: `public` means accessible everywhere, `private` restricts access to the class itself, and `protected` allows access within the same package plus subclasses. They’re the backbone of encapsulation, controlling who sees what.

Question 7

What is the `toString()` method?

Accepted Answer

The `toString()` method, from `Object`, returns a string representation of an object—by default, it’s a cryptic class name and hash. Override it to provide meaningful output, like for debugging or logging. It’s called implicitly by `System.out.println()` on objects.

Question 8

What is encapsulation in Java?

Accepted Answer

Encapsulation is bundling data (fields) and methods that operate on it into a single unit—a class—while hiding the internals using access modifiers like `private`. You expose only what’s needed via public getters and setters. It’s like a capsule: protects data and controls access.

Question 9

What is the `instanceof` operator?

Accepted Answer

The `instanceof` operator checks if an object is an instance of a specific class or interface, returning a boolean. It’s useful for type checking before casting to avoid `ClassCastException`. You’ll see it in polymorphic code or when handling mixed collections.

Question 10

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

Accepted Answer

In Java, `==` checks if two variables reference the same object in memory, while `.equals()` compares the actual content or values, depending on its implementation. For primitive types, `==` is your only option, but with objects like Strings, use `.equals()` to compare values—otherwise, `==` might return false even if the content matches.

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