A DESCRIPTION OF THE PROBLEM :
'RWDictionary' example contains compile time error. The next piece of code cannot be compiled:

public String[] allKeys() {
        r.lock();
        try { return m.keySet().toArray(); }
        finally { r.unlock(); }
    }


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
it should be:
return m.keySet().toArray(new String[0]);
ACTUAL -
error: incompatible types
        try { return m.keySet().toArray(); }
                                       ^
  required: String[]
  found: Object[]

URL OF FAULTY DOCUMENTATION :
http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/locks/ReentrantReadWriteLock.html