Understanding and Fixing 'IllegalStateException' in Java During Thread Management

The 'IllegalStateException' in Java is thrown when a method is invoked at an illegal or inappropriate time.

It is often encountered in multithreaded applications when attempting to perform operations that violate the expected state of the thread or object.

This can happen in various situations, such as when attempting to change the state of a thread after it has already been started or when invoking methods out of the intended sequence.

For example, in thread management, trying to call start() on a thread that has already been started will trigger an IllegalStateException.

To resolve this error, carefully review the order in which thread-related methods are called.

Ensure that you are not calling methods like start(), join(), or interrupt() in an inappropriate sequence.

Always check the thread state before performing an operation to ensure it’s in the correct state for that operation.

It’s also essential to consider synchronization issues that can cause threads to enter an unexpected state.

Properly synchronizing your threads using synchronized blocks or higher-level concurrency utilities like ExecutorService or CountDownLatch can help manage thread states effectively.