In this and the following chapter, arrays, references and pointers are examined. These will prove essential to a more detailed discussion of objects and classes.

Data structures and arrays

An array constitutes a built-in (e.g. native to the compiler) data structure, which denotes a collection of related quantities with common ordering properties. Each object in an array must be of the same type and is accessible through an integer index. Other commonly occurring data structures include the following.

1. A bag – an unordered collection of objects.

2. A set – a bag in which no object can appear more than once.

3. A list – an object sequence that enables navigation between an object and its successor.

4. An ordered list – a list with the property that an object can be accessed through its position as well as by way of the neighboring object.

5. A sorted list – a list with elements stored according to a given ordering operation.

6. A key set– an object collection that employs a key such as a word or number to locate elements.

7. A stack – a container for which elements can be added or removed only at the first (top) position; that is, only the last element to be added is accessible at any given time.

8. A queue – a container constructed such that only the oldest (first) element in the container can be removed at any given time.