Java 21 Interview Questions and Answers

Ques 1. What are Virtual Thread in Java 21?

Virtual threads are JVM-managed lightweight threads that will help in writing high-throughput concurrent applications (throughput means how many units of information a system can process in a given amount of time). [JEP-425, JEP-436 and JEP-444] In Java 21, virtual threads are ready for production use.

With the introduction of virtual threads, it becomes possible to execute millions of virtual threads using only a few operating system threads. The most advantageous aspect is that there is no need to modify existing Java code. All that is required is instructing our application framework to utilize virtual threads in place of platform threads.

To create a virtual thread, using the Java APIs, we can use the Thread or Executors.

Example:

Runnable runnable = () -> System.out.println("Inside Runnable");

//1

Thread.startVirtualThread(runnable);

//2

Thread virtualThread = Thread.ofVirtual().start(runnable);

//3

var executor = Executors.newVirtualThreadPerTaskExecutor(); 

executor.submit(runnable);

Ques 2. What are Unnamed Patterns and Variables in Java 21?

It is common in some other programming languages (such as Python, Scala) that we can skip naming a variable that we will not use in the future.

Example:

public void print(Object o) {

  switch (o) {

    case Point(int x, int _) -> System.out.printf("The x position is : %d%n", x); // Prints only x

    //...

  }

}