What happens if the thread pool queue is full but a new task arrives?

A rejected execution handler (RejectedExecutionHandler) will be applied. Standard handlers include:

• AbortPolicy: Throws a RejectedExecutionException.
• DiscardPolicy: Silently discards the task.
• DiscardOldestPolicy: Discards the oldest task in the queue and attempts to execute the new one.
• CallerRunsPolicy: Executes the task in the calling thread.

The specific behavior depends on which handler was configured when creating the thread pool.