Why is the Java Memory Model needed?

The Java Memory Model (JMM) defines the rules for how threads interact with memory in Java programs. It describes how and when changes made by one thread become visible to others, and also guarantees the correct operation of multithreaded code.

Without the JMM, the behavior of multithreaded programs would be unpredictable due to compiler and processor optimizations that can change the order of operations. The JMM provides:

• Visibility rules for changes between threads.
• Guarantees of operation order (happens-before).
• Definitions of the key keywords volatile, synchronized, and final.

Thus, the JMM is essential for writing correct, predictable, and safe multithreaded code in Java.