Class Diagram ​

Classes and members ​

Declare a class with the class keyword, then add members one of two ways — colon statements (Animal : +int age) or a curly-brace block, as the BankAccount example shows. Both forms mix freely.

A trailing word after a method's parentheses is its return type (+deposit(amount) bool). Generic types are written with tildes: List~int~; a tilde suffix on the class name itself (class Square~Shape~) declares a generic class.

Members are classified automatically: anything with parentheses renders in the method compartment, everything else is an attribute.

classDiagram
    class BankAccount{
        +String owner
        +BigDecimal balance
        +deposit(amount) bool
        +withdrawal(amount) int
    }
    class Square~Shape~{
        int id
        List~int~ position
        setPoints(List~int~ points)
        getPoints() List~int~
    }

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Visibility ​

An optional marker before a member name sets its visibility:

Two more go after a method's parentheses: $ marks it static and * marks it abstract. On an attribute, a trailing $ means static.

classDiagram
    class Account{
        +String publicField
        -String privateField
        #String protectedField
        ~String packageField
        +staticMethod()$
        +abstractMethod()*
    }

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Relationships ​

A relationship is two classes joined by an arrow operator, with an optional : label describing it:

Arrowheads may sit on either end (A --|> B is inheritance read the other way), and two-way relations (A <--> B) are supported.

classDiagram
    classA <|-- classB : inheritance
    classC *-- classD : composition
    classE o-- classF : aggregation
    classG <-- classH : association
    classI -- classJ : link
    classK <.. classL : dependency
    classM <|.. classN : realization
    classO .. classP : dashed link

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Cardinality ​

Quote a multiplicity on either end of the arrow, right next to the class it describes: Customer "1" --> "*" Ticket. Common values are 1, 0..1, 1..*, *, n, and many.

classDiagram
    Customer "1" --> "*" Ticket
    Student "1" --> "1..*" Course
    Galaxy --> "many" Star : contains

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Annotations ​

A <<stereotype>> line as the first entry of a class body marks its kind — <<interface>>, <<abstract>>, <<Service>>, <<enumeration>> — and renders above the class name.

classDiagram
    class Shape{
        <<interface>>
        noOfVertices
        draw()
    }
    class Color{
        <<enumeration>>
        RED
        BLUE
        GREEN
    }

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Notes ​

note "text" attaches a free-floating note to the diagram; note for ClassName "text" pins it to a class. A <br/> inside the quoted text breaks lines.

classDiagram
    note "This is a general note"
    note for Duck "can fly<br/>can swim<br/>can help in debugging"
    class Duck{
        +quack()
    }

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Direction ​

direction sets the flow of the layout: TB (default), BT, LR, or RL.

classDiagram
    direction LR
    class Order
    class Customer
    Customer "1" --> "*" Order : places

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