The command sleep() is used in Java to pause the execution of a thread, executed by typing "sleep()", with a number inside the parentheses. The number represent the length of the pause. Threads are one of the mechanisms the Java platform uses to manage concurrency.
A Java application has at least one process. In turn, each process can have at least one thread. A thread provides an environment in which code statements can be executed. In addition to pausing the thread, sleep() makes processor time available for other threads in the application, or in other applications.
A thread called 'Thread' in the following line of code creates a 5-second pause: "Thread.sleep(5000)". After 5 seconds, the execution of the thread proceeds to the next line of code in the program.
The Thread object has two sleep() methods. One accepts milliseconds as a parameter (like in the example above). The other sleep() method accepts milliseconds as well as nanoseconds, allowing the programmer to provide very precise instructions about the length of the required pause.
While the program is able to provide very precise instructions to the sleep() method, the exact timing of the pause is determined by the operating system environment in which the Java application is running.