A TimeUnit represents time durations at a given unit of granularity and provides utility methods to convert across units, and to perform timing and delay operations in these units. A TimeUnit does not maintain time information, but only helps organize and use time representations that may be maintained separately across various contexts. A nanosecond is defined as one thousandth of a microsecond, a microsecond as one thousandth of a millisecond, a millisecond as one thousandth of a second, a minute as sixty seconds, an hour as sixty minutes, and a day as twenty four hours.

A TimeUnit is mainly used to inform time-based methods how a given timing parameter should be interpreted. For example, the following code will timeout in 50 milliseconds if the lock is not available:

 
 Lock lock = ...;
 if (lock.tryLock(50L, TimeUnit.MILLISECONDS)) ...

while this code will timeout in 50 seconds:

 
 Lock lock = ...;
 if (lock.tryLock(50L, TimeUnit.SECONDS)) ...

Note however, that there is no guarantee that a particular timeout implementation will be able to notice the passage of time at the same granularity as the given TimeUnit.

 
 public E poll(long timeout, TimeUnit unit)
     throws InterruptedException {
   synchronized (lock) {
     while (isEmpty()) {
       unit.timedWait(lock, timeout);
       ...
     }
   }
 }