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Java / Java Concurrency and Multi Threading in Java 17 and Java 21 Interview questions

What is multithreading in Java?

Multithreading is the ability of a Java program to run multiple threads concurrently within a single process, letting the JVM interleave or truly parallelize independent pieces of work across CPU cores.

Instead of executing tasks one after another on a single thread, a multithreaded application can, for example, keep a UI responsive while a background thread downloads data, or serve hundreds of client connections at once, each handled by its own thread or task.

Java supports multithreading natively through the Thread class, the Runnable/Callable interfaces, and the higher-level java.util.concurrent package, which since Java 21 also includes lightweight virtual threads for handling very large numbers of concurrent tasks efficiently.

The main benefits are better CPU utilization on multi-core hardware and improved application responsiveness, but they come with added complexity around synchronizing access to shared data.

What is the primary goal of multithreading?
Since which Java version are lightweight virtual threads available for high-volume concurrency?

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