| The last section introduces abstract data types (ADTs) as an abstract view to define properties of a set of entities. Object-oriented programming languages must allow to implement these types. Consequently, once an ADT is implemented we have a particular representation of it available.
| Consider again the ADT Integer. Programming languages such as Pascal, C, Modula-2 and others already offer an implementation for it. Sometimes it is called int or integer. Once you've created a variable of this type you can use its provided operations. For example, you can add two integers: