UML Class Diagrams and Notation

UML Class Diagrams and Notation

The Unified Modeling Language (UML) class diagram provides a standard visual representation of classes and their interrelationships.

The 3 Compartments of a Class Box

A standard UML class box is split into three horizontal sections:

1. Top: Class Name (italicized if abstract, or prefixed with «interface» if an interface).
2. Middle: Attributes (e.g. - balance: double).
3. Bottom: Operations / Methods (e.g. + deposit(amount: double): void).

Visibility Modifiers

Symbol	Visibility	Description
+	Public	Accessible from any class
-	Private	Accessible only within the declaring class
#	Protected	Accessible within package and subclasses
~	Package-private	Accessible only within the same package

Multiplicity Notation

Multiplicity indicates how many instances participate in a relationship:

• 1: Exactly one
• 0..1: Zero or one (optional)
• * or 0..*: Zero or many
• 1..*: One or more

Exercise 1

In a UML diagram, what does the symbol - preceding an attribute denote?

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Solution

It denotes private visibility, indicating the member is encapsulated and inaccessible to outside callers.