Functional Programming in Java, 2nd Edition

Delayed Initialization

In object-oriented programming, we ensure that objects are well constructed before any method calls. We encapsulate, ensure proper state transitions, and preserve the object’s invariants. This works well most of the time, but when parts of an object’s internals are heavyweight resources, we’ll benefit if we postpone creating them. This can speed up object creation, and the program doesn’t expend any effort creating things that may not be used.

The design decision to postpone creating part of an object shouldn’t burden the object’s users—it should be seamless. Let’s explore some ways to design lazy initialization.

A Familiar Approach

In the following example, we’ll craft a way to delay the creation of a heavyweight instance. ...