An Introduction to UML

COMS 103 section 4

13 January, 1999

Review• UML is a graphical “design” language.

• Symbols in UML have certain meanings.

• “Class” is a rectangle with three parts:– Name– Variables or Attributes– Methods

Review (continued)• Classes have different types of

“relationships”– Associations: existence-independent– Dependency: using-relationship– Aggregate: part-of, has, or whole-part

Inheritance Relationships• Define new classes in terms of old classes

• This can be a labor-saving mechanism

• Sometimes called an “is-a” relationship

• Example:– Consider a “computer system” – Refine to a pentium-class computer system– Refine further to a pentium II or Celeron

Inheritance Example Diagram

Computer System

Pentium-Class System Macintosh

Pentium II Celeron

SimulateComputerOperation

Inheritance Terminology• Parent/Child

• Ancestor/descendent

• Superclass/Subclass

• Generalization/Specialization– Arrows point toward the more general class– “Inherit” is a verb, as in:

• class A inherits from class B

– “Inherited” is an adjective, as in:• method doit() is inherited from class B

Inheritance Notation

• class superclass { void m1(); }

• class subclass extend superclass { void m2(); }

• Instance creation:– superclass s1 = new superclass();– subclass s2 = new subclass();

• Reference:– s2.m1(); – s2.m2();

Overriding Superclass Names

• Use Same Name

• “super” notation

Pentium-class

doInstruction(int i)

Pentium-II

doInstruction(int i)

void m1() { super.m1(); // other m1 work}

Inheritance Example Diagram

Computer System

Pentium-Class System

doInstruction()

Macintosh

Pentium II

doInstruction()

Celeron

doInstruction()

Which “Relationship” to use?• Use Aggregate when creating an instance of

one class without the other doesn’t make sense.

• Use Dependency when one class provides a service to the other.

• Use Association when neither class depends upon the other, but there is a relationship.

• Use Inheritance when one class is a special case of the other.

Relationship Notation Review• Aggregate:

• Dependency:

• Association:

• Inheritance: