Attempts to acquire a lock on the given region of this channel's file.

This method does not block. An invocation always returns immediately, either having acquired a lock on the requested region or having failed to do so. If it fails to acquire a lock because an overlapping lock is held by another program then it returns null. If it fails to acquire a lock for any other reason then an appropriate exception is thrown.

Parameters:

position		The position at which the locked region is to start; must be non-negative
size		The size of the locked region; must be non-negative, and the sum position +  size must be non-negative
shared		true to request a shared lock, false to request an exclusive lock

Returns:  A lock object representing the newly-acquired lock, or null if the lock could not be acquired because another program holds an overlapping lock

Exceptions:

IllegalArgumentException		If the preconditions on the parameters do not hold
ClosedChannelException		If this channel is closed
OverlappingFileLockException		If a lock that overlaps the requested region is already held by this Java virtual machine, or if another thread is already blocked in this method and is attempting to lock an overlapping region of the same file
NonReadableChannelException		If shared is true but this channel was not opened for reading
NonWritableChannelException		If shared is false but this channel was not opened for writing
IOException		If some other I/O error occurs

See also:
lock(Object,CompletionHandler), lock(long,long,boolean,Object,CompletionHandler), tryLock()