Chapter 2 Lesson 4: Modeling Relationship Among Classes

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Chapter 2 Lesson 4 Modeling Relationship Among
Classes

• Inheritance

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Last Time

• Classes
• Objects
• Message Passing
• Modularity
• Abstraction
• Encapsulation
• Polymorphism

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Modeling Relationship and Structures

• Class diagrams used to model static Structures of
  Object-Oriented Software Systems and relationship
  among classes
• Class diagrams consists of
• A set of nodes that represent classes and
  interfaces
• A set of links that represent relationships among
  classes

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Relationship that can Modeled using Class Diagrams

• Inheritance, including extension and
  implementation
• Association, including aggregation and
  composition
• Dependency

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Inheritance

• Inheritance defines a relationship among classes
  and interfaces.
• There a several forms of inheritance
  relationship
• Extension relation between two classes. When
  class C2 extends class C1, class C2 is known as a
  subclass of class C1, and class C1 is known as a
  superclass of class C2
• The extension relationship between two
  interfaces. When interface I2 extends interface
  I1, interface I2 is known as a subinterface of
  interface I1, interface I1 is known as a
  superinterface of interface I2

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Inheritance

• The implementation relationship between a class
  and an interface. When class C2 implements
  interface I1, class C2 is known as an
  implementation of interface I1

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Inheritance
Interface

• The implementation relationship between a class
  and an interface. When class C2 implements
  interface I1, class C2 is known as an
  implementation of interface I1
• Other examples blender, car, bike, etc.

Code Java, Classes gets implemented
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UML Terminology for Inheritance

• Specialization ? Extension
• Generalization ? the inverse of specialization
• Realization ? Implementation

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Graphical Representation of Inheritance
Superclass
Superinterface
Interface
Subclass
Subinterface
Implementation
Extension Of interfaces
Implementation of Interfaces
Extension of classes
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Graphical Representation of Inheritance

• Extension relationship solid line
• Implementation relationship dashed line
• In class diagrams
• Regular class, fields methods Regular Roman
  fonts Example TriangleClass
• Interface and methods in italic fonts

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Conceptual Model of Inheritance

• Inheritance Models the is-a(n) relationship in
  the real world, i.e., if C2 is a
  subclass/subinterface/implementation of C1, then
  every instance of C1 is an instance of C2, and
  everything that applies to instances of C1 also
  applies to instances of C2
• Extension relationship between classes commonly
  associated with notion of reusing or sharing the
  implementation (i.e., fields and methods) of the
  superclass by its subclass

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Class Diagram Inheritance Relation Among Classes
Representing U.S Government
U.S. Government
Congress
Executive
Judicial
Senate
House
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Inheritance Levels of Abstraction

• Superclass represents more general abstractions
• Subclasses Represents more specialized
  abstraction