For standard programming techniques functions are the most important parts. They contain a sequence of statements which manipulate certain data structures. The main tool for abstraction is the usage of subprograms, this allows to use the same statements at different locations and divide one task into different operations.
In contrast to sequential programming the data structures are the central elements of object-oriented programming. The data is mentioned as individual objects in a certain state. According to their structure each object belongs to exactly one class. It is referenced as an instance of this class. A number of operations (methods) are assigned to each class, which modify the state of the corresponding instances. Moreover the classes themselves are mentioned as objects, because there exist special methods, which operate on classes, e.g. create a new instance.
The aim of object-oriented programming is to transform the objects from an initial to a final state by the application of appropriate methods.
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