What Is an Object

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A class is a data type that encapsulates data and operations on data in a single unit. Before object-oriented programming, data and operations (functions) were treated as separate elements. An object is an instance of a class. That is, it is a value whose type is a class. The term object is often used more loosely in this documentation and where the distinction between a class and an instance of the class is not important, the term "object" may also refer to a class.

You can begin to understand objects if you understand Pascal records or structures in C. Records are made of up fields that contain data, where each field has its own type. Records make it easy to refer to a collection of varied data elements.

Objects are also collections of data elements. But objects - unlike records - contain procedures and functions that operate on their data. These procedures and functions are called methods.

An object's data elements are accessed through properties. The properties of many Delphi objects have values that you can change at design time without writing code. If you want a property value to change at run time, you need to write only a small amount of code.

The combination of data and functionality in a single unit is called encapsulation. In addition to encapsulation, object-oriented programming is characterized by inheritance and polymorphism. Inheritance means that objects derive functionality from other objects (called ancestors); objects can modify their inherited behavior. Polymorphism means that different objects derived from the same ancestor support the same method and property interfaces, which often can be called interchangeably.


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