Java Executor Framework real-time interview questions with answers

What is the Java Executor Framework?

The Java Executor Framework is a set of interfaces and classes in Java that simplify the task of writing concurrent code. It provides a way to manage and control threads and thread pools, as well as a way to execute tasks asynchronously.

What are the benefits of using the Java Executor Framework?

The Java Executor Framework provides a number of benefits, including:

• Simplified thread management and control
• Improved performance through the use of thread pools
• Reduced memory usage through the reuse of threads
• Simplified asynchronous execution of tasks

What are the different types of Executor interfaces in Java?

The different types of Executor interfaces in Java are:

• Executor: The simplest interface that defines the execute() method for executing tasks.
• ExecutorService: An extension of the Executor interface that provides additional methods for managing the execution of tasks, such as shutting down the executor.
• ScheduledExecutorService: An extension of the ExecutorService interface that supports scheduling of tasks to be executed at a future time.

What is the difference between a Callable and a Runnable in Java?

main difference between a Callable and a Runnable in Java is that a Callable can return a result and throw an exception, whereas a Runnable cannot. The Callable interface defines a single method, call(), that returns a result and can throw an exception, whereas the Runnable interface defines a single method, run(), that does not return a result and cannot throw an exception.

How do you create a ScheduledExecutorService in Java?

we can create a ScheduledExecutorService in Java using the Executors.newScheduledThreadPool() method. For example, to create a ScheduledExecutorService with a pool size of 5 threads, you can use the following code:

ScheduledExecutorService executor = Executors.newScheduledThreadPool(5);

What is the difference between schedule() and scheduleAtFixedRate() methods in the ScheduledExecutorService interface

The schedule() method in the ScheduledExecutorService interface is used to schedule a task to be executed once at a specific time in the future, whereas the scheduleAtFixedRate() method is used to schedule a task to be executed at a fixed rate. The schedule() method takes a delay time as input, whereas the scheduleAtFixedRate() method takes an initial delay time and a period time as input.

What is the purpose of the invokeAll() method in the ExecutorService interface

The invokeAll() method in the ExecutorService interface is used to submit a collection of tasks for execution and wait for all tasks to complete. It returns a list of Future objects that can be used to retrieve the results of the tasks once they are complete.

What is the purpose of the invokeAny() method in the ExecutorService interface

The invokeAny() method in the ExecutorService interface is used to submit a collection of tasks for execution and wait for the first task to complete. It returns the result of the first task that completes successfully. If any of the tasks throw an exception, the invokeAny() method throws an ExecutionException.

What is a thread pool in Java?

thread pool is a collection of threads that are created and managed by an ExecutorService. Instead of creating a new thread every time a task needs to be executed, the ExecutorService reuses existing threads from the thread pool, resulting in improved performance and reduced memory usage.

How do you create a thread pool in Java?

You can create a thread pool in Java using the Executors class, which provides factory methods for creating different types of thread pools. For example, to create a fixed-size thread pool with five threads, you can use the following code:

What is the difference between submit() and execute() methods in the Executor Framework? A: The submit() method is used to submit a task for execution and returns a Future object that can be used to check the status of the task and retrieve its result. The execute() method, on the other hand, is used to submit a task for execution without returning any result. If the task throws an exception, it is logged but not propagated to the calling thread.

How do you shut down an ExecutorService in Java?

You can shut down an ExecutorService in Java using the shutdown() method, which initiates a graceful shutdown of the ExecutorService. This method will allow all tasks that have been submitted to the ExecutorService to complete, but it will not accept any new tasks. Once all tasks have completed, the ExecutorService will terminate.

What is a Callable in Java?

Callable is a functional interface in Java that represents a task that can be executed asynchronously and returns a result. It is similar to a Runnable, but the call() method returns a result, whereas the run() method does not.

What is a Future in Java?

Future is an interface in Java that represents the result of an asynchronous computation. It provides methods for checking the status of the computation, cancelling the computation, and retrieving the result once it is available.

What is the purpose of the CompletionService interface in Java?

CompletionService interface in Java provides a way to retrieve completed tasks in the order in which they finish. This can be useful in situations where the order of task completion is important, such as in a web crawler that needs to process pages in the order in which they are downloaded.

What is the purpose of the RejectedExecutionHandler interface in Java

The RejectedExecutionHandler interface in Java is used to handle tasks that cannot be executed by an ExecutorService. It provides a way to customize the behavior of the ExecutorService when it encounters a situation where it cannot accept a task for execution, such as when the thread pool has reached its maximum capacity.