The {@link edu.emory.mathcs.backport.java.util.concurrent.locks.Lock} interface supports locking disciplines that differ in semantics (reentrant, fair, etc), and that can be used in non-block-structured contexts including hand-over-hand and lock reordering algorithms. The main implementation is {@link edu.emory.mathcs.backport.java.util.concurrent.locks.ReentrantLock}.
The {@link edu.emory.mathcs.backport.java.util.concurrent.locks.ReadWriteLock} interface similarly defines locks that may be shared among readers but are exclusive to writers. Only a single implementation, {@link edu.emory.mathcs.backport.java.util.concurrent.locks.ReentrantReadWriteLock}, is provided, since it covers most standard usage contexts. But programmers may create their own implementations to cover nonstandard requirements.
The {@link edu.emory.mathcs.backport.java.util.concurrent.locks.Condition} interface describes condition variables that may be associated with Locks. These are similar in usage to the implicit monitors accessed using Object.wait, but offer extended capabilities. In particular, multiple Condition objects may be associated with a single Lock. To avoid compatibility issues, the names of Condition methods are different than the corresponding Object versions. @since 1.5