1. What is concurrency in Java?
    • Concurrency in Java is the ability to run several programs or several parts of a program in parallel to maximize the utilization of CPU resources.
  2. How do you create a thread in Java?
    • You can create a thread in Java by either extending the Thread class or implementing the Runnable interface.
  3. What is the difference between the Runnable interface and the Thread class?
    • Runnable is an interface that allows a class to be executed by a thread. Thread is a class that represents a thread of execution. Implementing Runnable is preferred because it supports composition and avoids the Java single inheritance issue.
  4. How do you start a thread in Java?
    • To start a thread, you instantiate a Thread object and call its start() method.
  5. What does the synchronized keyword mean?
    • The synchronized keyword is used to ensure that a method or block is accessed by only one thread at a time.
  6. What is the difference between wait() and sleep() in Java?
    • wait() releases the lock or monitor, while sleep() does not. wait() is called on an object, but sleep() is called on a Thread.
  7. What is a deadlock?
    • A deadlock is a situation where two or more threads are blocked forever, waiting for each other.
  8. How can you prevent a deadlock in Java?
    • You can prevent deadlocks by avoiding nested locks, using a lock ordering convention, or using a timeout when trying to obtain locks.
  9. What is the volatile keyword in Java?
    • The volatile keyword indicates that a variable’s value will be modified by different threads and ensures the visibility of changes to variables across threads.
  10. What are atomic operations in Java?
    • Atomic operations are operations that are performed in a single unit of task without interference from other operations. Java provides atomic classes in the java.util.concurrent.atomic package, such as AtomicInteger, for this purpose.
  11. What is the Executor Framework in Java?
    • The Executor Framework is a framework provided by the java.util.concurrent package that simplifies the execution of tasks in asynchronous mode.
  12. How does the synchronized keyword differ from locks in Java?
    • While synchronized is a keyword that provides a built-in locking mechanism, locks (from the java.util.concurrent.locks package) offer more sophisticated thread synchronization control through lock and unlock methods.
  13. What is a Semaphore in Java?
    • A Semaphore is a concurrency utility that controls access to a shared resource through the use of counters.
  14. What is a CountDownLatch in Java?
    • A CountDownLatch is used to make one thread wait until one or more threads have completed their operations.
  15. What is a CyclicBarrier in Java?
    • A CyclicBarrier is a synchronization mechanism that allows a set of threads to all wait for each other to reach a common barrier point.
  16. Explain the producer-consumer problem in Java.
    • The producer-consumer problem is a classic example of a multi-process synchronization problem, where the goal is to ensure that the producer doesn’t produce items when the buffer is full, and the consumer doesn’t consume items when the buffer is empty.
  17. What is ThreadLocal in Java?
    • ThreadLocal is a class that provides thread-local variables. Each thread accessing such a variable has its own, independently initialized copy of the variable.
  18. How do you use the ReentrantLock class in Java?
    • ReentrantLock is used for locking with the same basic behavior and semantics as the implicit monitor lock accessed using synchronized methods and statements, but with extended capabilities.
  19. What are the key components of the Java Concurrency API?
    • Key components include ExecutorService, Locks, Atomic Variables, Futures, Blocking Queues, and the Fork/Join Framework.
  20. What is the Fork/Join Framework in Java?
    • It is a framework designed for work-stealing algorithms, facilitating parallel programming by recursively breaking tasks into smaller tasks and using a pool of threads to execute these tasks.
  21. How can you stop a thread in Java?
    • Stopping a thread safely is done by using interrupt signals (interrupt() method) and checking the interrupt status of the thread.
  22. What is Thread.join() in Java?
    • The join() method allows one thread to wait for the completion of another.
  23. What is the significance of the ConcurrentHashMap in Java?
    • ConcurrentHashMap is a thread-safe variant of HashMap that does not lock the Map for reads and reduces lock contention for writes.
  24. How does synchronized block differ from synchronized method?
    • A synchronized block provides synchronization only for the block of code it encloses, offering more granular control, while a synchronized method locks the entire object or class.
  25. What is a ReadWriteLock in Java?
    • A ReadWriteLock allows a resource to be accessed by multiple readers or a single writer at a time, but not both.
  26. Describe the wait, notify, and notifyAll methods in Java.
    • These methods are used for communication between threads. wait causes the current thread to wait until another thread invokes notify or notifyAll. notify wakes up a single waiting thread, while notifyAll wakes up all waiting threads.
  27. What are the advantages of using the Executor Framework?
    • It simplifies the execution of tasks in asynchronous mode, helps manage a pool of threads, and reduces the need for manual thread management.
  28. How does the synchronized keyword ensure visibility and atomicity?
    • It ensures that changes made by one thread are visible to others, and it provides atomicity by locking the critical section so that only one thread can execute it at a time.
  29. What is the purpose of BlockingQueue in Java?
    • BlockingQueue is a type of queue that supports operations that wait for the queue to become non-empty when retrieving