The singleton design pattern

The singleton design pattern ensures that a class has only one object instance in the entire application. It introduces a global state in the applications it is used in.

A singleton object can be initialized using different strategies—lazy initialization or eager initialization. This all depends on the intended use, the time it takes an object to be initialized, and so on.

An example class diagram

Singletons are another example of design patterns, which are supported out of the box by the Scala programming language syntax. We achieve this by using the object keyword. In this case, again, providing a class diagram is not necessary, so we will step right into the example in the next subsection.

A code example

The aim of this example is to show how to create singleton instances in Scala and have an understanding of when exactly instances are created in Scala. We will look at a class called StringUtils, that provides different utility methods related to strings:

object...