Trying to control thread interaction by periodically calling Thread.sleep within a loop while waiting for a condition to be satisfied is less effective than waiting for a notification. This is because the waiting thread may either sleep for an unnecessarily long time or wake up too frequently. This approach may also result in race conditions and, therefore, incorrect code.

Trying to control thread interaction by repeatedly checking a synchronized data structure without calling Thread.sleep or waiting for a notification may waste a lot of system resources and cause noticeable performance problems.

See if communication between threads can be improved by using either of the following solutions:

The java.util.concurrent library, preferably
The Object.wait and Object.notifyAll methods

If following one of these recommendations is not feasible, ensure that race conditions cannot occur and precise timing is not required for program correctness.

In the following example, the Receiver thread sleeps for an unnecessarily long time (up to five seconds) until it has received the message.

In the following modification of the above example, the Receiver thread uses the recommended approach of waiting for a notification that the message has been sent. This means that the thread can respond immediately instead of sleeping.

J. Bloch, Effective Java (second edition), Item 72. Addison-Wesley, 2008.

Java API Specification: Object.wait(), Object.notifyAll(), java.util.concurrent.

The Java Tutorials: Guarded Blocks, High Level Concurrency Objects.