Can you name three examples that ensure happens-before?

In Java, happens-before is a relation that guarantees visibility and order of operations between threads. Three examples that ensure happens-before:

1. Executing unlock() on a monitor happens-before a subsequent lock() on the same monitor.
2. Writing to a volatile variable happens-before subsequent reading of that same volatile variable.
3. Thread completion (Thread.join()) happens-before the continuation of the thread that called join().

These rules help prevent data visibility issues in a multithreaded environment.