What is an object?

The first computers used arrays for storing data. By 1965, Simula had introduced a new way of programming using an object-oriented approach. Programs were built from fundamental constructs called objects.

An object has attributes (variables) and methods (subroutines). Like a record data structure, an object may contain many related attributes of different data types. Unlike records, attributes of an object can be public or private; a similar concept to the scope of a variable being global or local. Public attributes are like global variables and can be used and accessed by other objects. Private attributes can only be accessed by methods of the object – this is known as encapsulation.

Over the years, the concept of object-oriented programming (OOP) changed from its original intentions of self-contained data structures – messages being passed between objects – into a more complex model. Today, OOP includes many additional features like sub-classes, inheritance and polymorphism, which are beyond the scope of this book. Instead, we will look at how objects are used as data structures for algorithms.