Question 1

What is the `Comparator` interface?

Accepted Answer

The `Comparator` interface provides a way to sort objects without changing their class, unlike `Comparable`. You implement `compare()` to define custom ordering—like sorting by age instead of name. It’s more flexible and often used with lambdas in modern Java.

Question 2

What is the `AtomicInteger` class?

Accepted Answer

The `AtomicInteger` class provides thread-safe operations on an integer without locks, using low-level CPU instructions. Methods like `incrementAndGet()` ensure atomic updates—perfect for counters in multi-threaded apps without the overhead of `synchronized`.

Question 3

What is the `transient` keyword used for?

Accepted Answer

The `transient` keyword marks a field to be excluded from serialization, so its value isn’t saved when an object is serialized. It’s useful for temporary data or sensitive info like passwords that shouldn’t persist—like a secret you keep in memory only.

Question 4

What is the `CyclicBarrier` class?

Accepted Answer

The `CyclicBarrier` makes a group of threads wait until all reach a common point, then releases them—reusable unlike `CountDownLatch`. It’s like a team huddle—everyone waits, then proceeds together—ideal for parallel tasks.

Question 5

What is a Java thread pool?

Accepted Answer

A thread pool manages a set of reusable threads to execute tasks, avoiding the overhead of creating new threads repeatedly. The `ExecutorService` framework provides implementations like `ThreadPoolExecutor`. It’s efficient for apps with many short-lived tasks—like web servers.

Question 6

What is a Java inner class?

Accepted Answer

An inner class is a class defined inside another class, giving it access to the outer class’s members—even `private` ones. It’s useful for grouping related logic, like event handlers. Types include static, non-static, local, and anonymous.

Question 7

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 8

What are Java Streams?

Accepted Answer

Java Streams, added in Java 8, let you process collections functionally with operations like filter, map, and reduce. They’re lazy—nothing happens until a terminal operation like `collect()` triggers them—and can run in parallel for performance. They make code cleaner but take practice to master.

Question 9

What is the `Path` interface in Java?

Accepted Answer

The `Path` interface (from `java.nio.file`) represents a file system path—like a file or directory location. You create it with `Paths.get()` and use it with `Files` for operations. It’s more robust than `File` for modern I/O.

Question 10

What is the `Class` class in Java?

Accepted Answer

The `Class` class represents a class or interface at runtime—think of it as metadata about a type. You get it via `.class` syntax or `getClass()`, and it’s used in reflection to inspect or instantiate objects dynamically. It’s the backbone of Java’s reflective abilities.

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