Basic Java Questions

1. What are the main features of Java?
2. Explain the difference between JDK, JRE, and JVM.
3. What is the difference between == and .equals() in Java?
4. What are the data types supported by Java?
5. Explain the concept of Java memory model.

Object-Oriented Programming (OOP) in Java

1. What are the four principles of Object-Oriented Programming?
2. What is polymorphism? Provide an example.
3. Explain the concept of inheritance in Java.
4. What is encapsulation? How is it implemented in Java?
5. What is abstraction? How do you achieve it in Java?

Advanced Java Topics

1. What are Java collections? Explain the difference between ArrayList and LinkedList.
2. What is the difference between HashMap and TreeMap?
3. What are Generics in Java? Why are they used?
4. Explain the concept of HashCode and equals method.
5. What is the significance of the final keyword in Java?

Concurrency and Multithreading

1. How do you create a thread in Java?
2. Explain the difference between synchronized and ConcurrentHashMap.
3. What is a deadlock? How can you prevent it?
4. Describe the ExecutorService and its benefits.
5. What are Callable and Future? How are they used?

Java API and Libraries

1. What are the major Java API packages?
2. Explain the Java Stream API. Provide an example.
3. What is Java NIO? How is it different from the traditional I/O?
4. What is the purpose of the java.lang package?
5. How do you handle exceptions in Java? What is the difference between checked and unchecked exceptions?

Design Patterns

1. What are design patterns? Name a few commonly used design patterns in Java.
2. Explain the Singleton pattern.
3. What is the Factory pattern? Provide an example.
4. Describe the Observer pattern. How is it implemented in Java?
5. What is the difference between AbstractFactory and Builder pattern?

Performance and Optimization

1. How do you optimize the performance of a Java application?
2. What is garbage collection in Java? How does it work?
3. Explain the concept of JVM tuning.
4. What are the common JVM flags used for performance tuning?
5. How do you profile a Java application?

Practical Coding Questions

1. Write a program to reverse a string in Java.
2. How do you find the factorial of a number in Java?
3. Write a Java program to check if a given number is prime.
4. Implement a thread-safe singleton pattern.
5. Write code to merge two sorted arrays.

System Design and Architecture

1. How would you design a URL shortening service?
2. Explain the architecture of a high-traffic web application.
3. How do you design a caching layer in Java?
4. Discuss the advantages and disadvantages of microservices architecture.
5. How would you design a distributed system with fault tolerance?