What is the connection between constructor call and the guarantees of execution order (Happens Before)?

In the Java memory model, calling a constructor initializes an object, and after the constructor completes, a so-called "happens-before" relationship occurs between the completion of the constructor and the visibility of the object to other threads.

This means that if one thread creates an object and fully executes the constructor, and then passes the reference to another thread, the second thread is guaranteed to see the fully initialized object with correct field values.

In other words, the completion of the constructor establishes a synchronization point after which other threads see all changes made in the constructor. This is important for thread safety and preventing the reading of partially initialized objects.