Java defines a happens-before relationship as follows.
Two actions can be ordered by a happens-before relationship. If one action happens-before another, then the first is visible to and ordered before the second.
According to this, if there is a happens-before relationship between a write and read operation, the results of a write by one thread are guaranteed to be visible to a read by another thread. Therefore, we will be able to maintain the memory consistency if we are able to have the happens-before relationship between our actions.