Generalization
Generalization is a mechanism for combining similar classes of objects into a single, more general class. Generalization is a bottom-up process. Generalization and inheritance are powerful abstractions for sharing similarities among classes while preserving their differences.
Some Forms of Generalization
1. Hierarchy: In the case of hierarchy, the commonalities are organized into a tree structured form. At the root of any subtree are found all the attributes and behavior common to all of the descendents of that root.
2. Genericity: In this case, the commonality is expressed with the aid of a parameter. Various specializations are distinguished by what they provide for the parameter. For example, using genericity it is possible to represent the common properties of a “stack” through the generalization of a “stack of anything”, where “anything” represents the parameter.
3. Polymorphism: Polymorphism captures commonality in algorithms. Polymorphism allows the nested logic (or case statement) to be collapsed to a single case in which the different object types are treated in a uniform manner.
4. Patterns: A pattern expresses a general solution (the key components and relationships) to a commonly occurring design problem. The attributes and behavior of the individual components are only partially defined to allow the pattern to be interpreted and applied to a wide range of situations.
Inheritance
The generalization/specialization relationship is implemented in object-oriented programming languages with inheritance. Inheritance is the implementation mechanism for the generalization/specialization relationship. In single inheritance a subclass has only one superclass. In multiple inheritance a subclass has two or more superclasses.
One object-oriented concept that helps objects work together is inheritance. Inheritance defines relationships among classes in an object-oriented language. In other words, Inheritance is the mechanism used in object-oriented programming (OOP) languages to permit a subclass to share attributes and operations defined in the superclasses.
For example the subclass Car can share the attributes and operations from the superclass Vehicle. The subclass Car may add attributes and operations.
