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Question number: 416

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Describe in Detail

What is Object Oriented model?


The Object-Oriented Model

  • An object contains values stored in instance variables within the object.

  • Unlike the record-oriented models, these values are themselves objects.

  • Thus objects contain objects to an arbitrarily deep level of nesting.

  • An object also contains bodies of code that operate on the the object.

  • These bodies of code are called methods.

  • Objects that contain the same types of values and the same methods are grouped into classes.

  • A class may be viewed as a type definition for objects.

  • Analogy: the programming language concept of an abstract data type.

  • The only way in which one object can access the data of another object is by invoking the method of that other object.

  • This is called sending a message to the object.

  • Internal parts of the object, the instance variables and method code, are not visible externally.

  • Result is two levels of data abstraction.

    For example, consider an object representing a bank account.

  • The object contains instance variables number and balance.

  • The object contains a method pay-interest which adds interest to the balance.

  • Under most data models, changing the interest rate entails changing code in application programs.

  • In the object-oriented model, this only entails a change within the pay-interest method.