How has ThreadLocal changed in recent Java versions?

The ThreadLocal class has undergone various improvements and changes in recent Java versions. It allows the creation of variables that are isolated to individual threads, ensuring that each thread has its own unique copy of a variable.

In Java 8, the performance of ThreadLocal was optimized, particularly with regard to its expiration and cleanup processes, leading to a reduction in memory leaks associated with thread-local variables. Java 9 introduced some usability improvements, such as enhanced API methods for better management of ThreadLocal values.

With Java 11 and newer versions, ThreadLocal continues to be a vital tool for managing thread-specific data, especially in concurrent applications, with ongoing refinements to its behavior and performance in handling large numbers of threads.