Lazy initialization in software engineering is when we delay the instantiation of an object or a variable until the first time we need it. The idea behind this is to defer or even avoid some expensive operations.
In other languages, such as Java, lazy initialization is often used in conjunction with the factory method design pattern. This method usually checks whether the object/variable we want to use is initialized, if not it initializes the object and finally returns it. In consecutive uses, the already initialized object/variable is returned.
The Scala programming language has a built-in support for lazy initialization. It makes use of the lazy keyword. That's why providing a class diagram in this case is pointless.