Java interview questions related to threads are a common topic in technical interviews. Understanding the concepts of threads, synchronization, and concurrency is crucial for any Java developer. In this article, we will discuss some of the most frequently asked Java interview questions about threads, providing insights and explanations to help you prepare for your next interview.
1. What is a thread in Java?
A thread in Java is a lightweight sub-process that runs concurrently with other threads. It allows multiple tasks to be executed simultaneously, improving the performance of an application. In Java, threads are represented by the `Thread` class.
2. How do you create a thread in Java?
There are two ways to create a thread in Java:
– By extending the `Thread` class and overriding the `run()` method.
– By implementing the `Runnable` interface and passing an instance of it to a `Thread` object.
3. What is the difference between a process and a thread?
A process is an instance of a program that is being executed, and it has its own memory space. On the other hand, a thread is a sequence of instructions within a process that shares the same memory space. Threads are more lightweight than processes, as they do not require a separate memory space.
4. What is a thread pool in Java?
A thread pool is a collection of pre-initialized threads that can be reused to execute tasks. It helps in managing the creation and termination of threads, reducing the overhead of thread creation and destruction. Java provides the `ExecutorService` interface and its implementations to create thread pools.
5. What is synchronization in Java?
Synchronization in Java is a mechanism that allows multiple threads to access shared resources without causing data inconsistency. It ensures that only one thread can access a synchronized block or method at a time. The `synchronized` keyword is used to achieve synchronization in Java.
6. What are the different types of synchronization in Java?
There are two types of synchronization in Java:
– Synchronized methods: A method is synchronized if the `synchronized` keyword is used before the method declaration.
– Synchronized blocks: A block of code is synchronized if the `synchronized` keyword is used before the block of code.
7. What is a deadlock in Java?
A deadlock in Java occurs when two or more threads are blocked indefinitely, waiting for each other to release resources. This happens when each thread holds a resource and is waiting for another resource that is held by another thread.
8. What is a livelock in Java?
A livelock in Java is a situation where two or more threads are actively contending for resources but are unable to make any progress. Unlike a deadlock, the threads in a livelock are not blocked; they are just competing for resources in a way that prevents any progress.
9. What is a thread-safe collection in Java?
A thread-safe collection in Java is a collection that can be safely used by multiple threads without the need for external synchronization. Java provides several thread-safe collections, such as `Vector`, `ArrayList`, `HashMap`, and `ConcurrentHashMap`.
10. What is the use of the `volatile` keyword in Java?
The `volatile` keyword in Java ensures that a variable is read from and written to main memory, not from a thread’s cache. This is useful when a variable is shared among multiple threads, and you want to ensure that all threads have the most up-to-date value of the variable.
By understanding these Java interview questions about threads, you will be well-prepared to discuss these concepts with confidence during your technical interviews.
