Class Diagram

Declaring element

@startuml
abstract        abstract
abstract class  "abstract class"
annotation      annotation
circle          circle
()              circle_short_form
class           class
diamond         diamond
<>              diamond_short_form
entity          entity
enum            enum
exception       exception
interface       interface
metaclass       metaclass
protocol        protocol
stereotype      stereotype
struct          struct
@enduml

[Ref. for protocol and struct: GH-1028, for exception: QA-16258]

Relations between classes

Relations between classes are defined using the following symbols :

Type Symbol Drawing

Extension

`+<

--+`

image::extends01.png[]

Composition

*--

image::sym03.png[]

Aggregation

o--

It is possible to replace -- by .. to have a dotted line.

Knowing those rules, it is possible to draw the following drawings:

@startuml
Class01 <|-- Class02
Class03 *-- Class04
Class05 o-- Class06
Class07 .. Class08
Class09 -- Class10
@enduml
@startuml
Class11 <|.. Class12
Class13 --> Class14
Class15 ..> Class16
Class17 ..|> Class18
Class19 <--* Class20
@enduml
@startuml
Class21 #-- Class22
Class23 x-- Class24
Class25 }-- Class26
Class27 +-- Class28
Class29 ^-- Class30
@enduml

Label on relations

It is possible to add a label on the relation, using :, followed by the text of the label.

For cardinality, you can use double-quotes "" on each side of the relation.

@startuml

Class01 "1" *-- "many" Class02 : contains

Class03 o-- Class04 : aggregation

Class05 --> "1" Class06

@enduml

You can add an extra arrow pointing at one object showing which object acts on the other object, using < or > at the begin or at the end of the label.

@startuml
class Car

Driver - Car : drives >
Car *- Wheel : have 4 >
Car -- Person : < owns

@enduml

Using non-letters in element names and relation labels

If you want to use link::unicode[non-letters] in the class (or enum…​) display name, you can either : * Use the as keyword in the class definition to assign an alias * Put quotes "" around the class name

@startuml
class "This is my class" as class1
class class2 as "It works this way too"

class2 *-- "foo/dummy" : use
@enduml

If an alias is assigned to an element, the rest of the file must refer to the element by the alias instead of the name.

Starting names with $

Note that names starting with $ cannot be hidden or removed later, because hide and remove command will consider the name a $tag instead of a component name. To later remove such elements they must have an alias or must be tagged.

@startuml
class $C1
class $C2 $C2
class "$C2" as dollarC2
remove $C1
remove $C2
remove dollarC2
@enduml

Also note that names starting with $ are valid, but to assign an alias to such element the name must be put between quotes "".

Adding methods

To declare fields and methods, you can use the symbol : followed by the field’s or method’s name.

The system checks for parenthesis to choose between methods and fields.

@startuml
Object <|-- ArrayList

Object : equals()
ArrayList : Object[] elementData
ArrayList : size()

@enduml

It is also possible to group between brackets {} all fields and methods.

Note that the syntax is highly flexible about type/name order.

@startuml
class Dummy {
  String data
  void methods()
}

class Flight {
   flightNumber : Integer
   departureTime : Date
}
@enduml

You can use {field} and {method} modifiers to override default behaviour of the parser about fields and methods.

@startuml
class Dummy {
  {field} A field (despite parentheses)
  {method} Some method
}

@enduml

Defining visibility

When you define methods or fields, you can use characters to define the visibility of the corresponding item:

Character Icon for field Icon for method Visibility

-

image::private-field.png[]

image::private-method.png[]

private

#

image::protected-field.png[]

image::protected-method.png[]

protected

~

image::package-private-field.png[]

image::package-private-method.png[]

package private

+

image::public-field.png[]

image::public-method.png[]

public

 
@startuml

class Dummy {
 -field1
 #field2
 ~method1()
 +method2()
}

@enduml

You can turn off this feature using the skinparam classAttributeIconSize 0 command :

@startuml
skinparam classAttributeIconSize 0
class Dummy {
 -field1
 #field2
 ~method1()
 +method2()
}

@enduml

Visibility indicators are optional and can be ommitted individualy without turning off the icons globally using skinparam classAttributeIconSize 0.

@startuml
class Dummy {
 field1
 field2
 method1()
 method2()
}

@enduml

In such case if you’d like to use methods or fields that start with -, #, ~ or + characters such as a destructor in some languages for Dummy class ~Dummy(), escape the first character with a \ character:

@startuml
class Dummy {
 field1
 \~Dummy()
 method1()
}

@enduml

Abstract and Static

You can define static or abstract methods or fields using the {static} or {abstract} modifier.

These modifiers can be used at the start or at the end of the line. You can also use {classifier} instead of {static}.

@startuml
class Dummy {
  {static} String id
  {abstract} void methods()
}
@enduml

Advanced class body

By default, methods and fields are automatically regrouped by PlantUML. You can use separators to define your own way of ordering fields and methods. The following separators are possible : -- .. == __.

You can also use titles within the separators:

@startuml
class Foo1 {
  You can use
  several lines
  ..
  as you want
  and group
  ==
  things together.
  __
  You can have as many groups
  as you want
  --
  End of class
}

class User {
  .. Simple Getter ..
  + getName()
  + getAddress()
  .. Some setter ..
  + setName()
  __ private data __
  int age
  -- encrypted --
  String password
}

@enduml

Notes and stereotypes

Stereotypes are defined with the class keyword, << and >>.

You can also define notes using note left of , note right of , note top of , note bottom of keywords.

You can also define a note on the last defined class using note left, note right, note top, note bottom.

A note can be also define alone with the note keywords, then linked to other objects using the .. symbol.

@startuml
class Object << general >>
Object <|--- ArrayList

note top of Object : In java, every class\nextends this one.

note "This is a floating note" as N1
note "This note is connected\nto several objects." as N2
Object .. N2
N2 .. ArrayList

class Foo
note left: On last defined class

@enduml

More on notes

It is also possible to use few HTML tags (See link::creole[Creole expression]) like :

  • <b>

  • <u>

  • <i>

  • <s>, <del>, <strike>

  • <font color="#AAAAAA"> or <font color="colorName">

  • <color:#AAAAAA> or <color:colorName>

  • <size:nn> to change font size

  • <img src="file"> or <img:file>: the file must be accessible by the filesystem

You can also have a note on several lines.

You can also define a note on the last defined class using note left, note right, note top, note bottom.

@startuml

class Foo
note left: On last defined class

note top of Foo
  In java, every class
  extends
  this one.
end note

note as N1
  This note is also
  on several
  words lines
  And this is hosted by 
end note

@enduml

Note on field (field, attribute, member) or method

It is possible to add a note on field (field, attribute, member) or on method.

⚠ Constraint

  • This cannot be used with top or bottom (only left and right are implemented)

  • This cannot be used with namespaceSeparator ::

Note on field or method

@startuml
class A {
{static} int counter
+void {abstract} start(int timeout)
}
note right of A::counter
  This member is annotated
end note
note right of A::start
  This method is now explained in a UML note
end note
@enduml

Note on method with the same name

@startuml
class A {
{static} int counter
+void {abstract} start(int timeoutms)
+void {abstract} start(Duration timeout)
}
note left of A::counter
  This member is annotated
end note
note right of A::"start(int timeoutms)"
  This method with int
end note
note right of A::"start(Duration timeout)"
  This method with Duration
end note
@enduml

[Ref. QA-3474 and QA-5835]

Note on links

It is possible to add a note on a link, just after the link definition, using note on link.

You can also use note left on link, note right on link, note top on link, note bottom on link if you want to change the relative position of the note with the label.

@startuml

class Dummy
Dummy --> Foo : A link
note on link #red: note that is red

Dummy --> Foo2 : Another link
note right on link #blue
this is my note on right link
and in blue
end note

@enduml

Abstract class and interface

You can declare a class as abstract using abstract or abstract class keywords.

The class will be printed in italic.

You can use the interface, annotation and enum keywords too.

@startuml

abstract class AbstractList
abstract AbstractCollection
interface List
interface Collection

List <|-- AbstractList
Collection <|-- AbstractCollection

Collection <|- List
AbstractCollection <|- AbstractList
AbstractList <|-- ArrayList

class ArrayList {
  Object[] elementData
  size()
}

enum TimeUnit {
  DAYS
  HOURS
  MINUTES
}

annotation SuppressWarnings

annotation Annotation {
  annotation with members
  String foo()
  String bar()
}


@enduml

[Ref. 'Annotation with members' Issue#458]

Hide attributes, methods…​

You can parameterize the display of classes using the hide/show command.

The basic command is: hide empty members. This command will hide attributes or methods if they are empty.

Instead of empty members, you can use: * empty fields or empty attributes for empty fields, * empty methods for empty methods, * fields or attributes which will hide fields, even if they are described, * methods which will hide methods, even if they are described, * members which will hide fields and methods, even if they are described, * circle for the circled character in front of class name, * stereotype for the stereotype.

You can also provide, just after the hide or show keyword: * class for all classes, * interface for all interfaces, * enum for all enums, * <<foo1>> for classes which are stereotyped with foo1, * an existing class name.

You can use several show/hide commands to define rules and exceptions.

@startuml

class Dummy1 {
  +myMethods()
}

class Dummy2 {
  +hiddenMethod()
}

class Dummy3 <> {
String name
}

hide members
hide <> circle
show Dummy1 methods
show <> fields

@enduml

Hide classes

You can also use the show/hide commands to hide classes.

This may be useful if you define a large link::preprocessing[!included file], and if you want to hide some classes after link::preprocessing[file inclusion].

@startuml

class Foo1
class Foo2

Foo2 *-- Foo1

hide Foo2

@enduml

Remove classes

You can also use the remove commands to remove classes.

This may be useful if you define a large link::preprocessing[!included file], and if you want to remove some classes after link::preprocessing[file inclusion].

@startuml

class Foo1
class Foo2

Foo2 *-- Foo1

remove Foo2

@enduml

Hide, Remove or Restore tagged element or wildcard

You can put $tags (using $) on elements, then remove, hide or restore components either individually or by tags.

By default, all components are displayed:

@startuml
class C1 $tag13
enum E1
interface I1 $tag13
C1 -- I1
@enduml

But you can: * hide $tag13 components:

@startuml
class C1 $tag13
enum E1
interface I1 $tag13
C1 -- I1

hide $tag13
@enduml

  • or remove $tag13 components:

@startuml
class C1 $tag13
enum E1
interface I1 $tag13
C1 -- I1

remove $tag13
@enduml

  • or remove $tag13 and restore $tag1 components:

@startuml
class C1 $tag13 $tag1
enum E1
interface I1 $tag13
C1 -- I1

remove $tag13
restore $tag1
@enduml

  • or remove * and restore $tag1 components:

@startuml
class C1 $tag13 $tag1
enum E1
interface I1 $tag13
C1 -- I1

remove *
restore $tag1
@enduml

Hide or Remove unlinked class

By default, all classes are displayed:

@startuml
class C1
class C2
class C3
C1 -- C2
@enduml

But you can: * hide @unlinked classes:

@startuml
class C1
class C2
class C3
C1 -- C2

hide @unlinked
@enduml

  • or remove @unlinked classes:

@startuml
class C1
class C2
class C3
C1 -- C2

remove @unlinked
@enduml

[Adapted from QA-11052]

Use generics

You can also use bracket < and > to define generics usage in a class.

@startuml

class Foo {
  int size()
}
Foo *- Element

@enduml

It is possible to disable this drawing using skinparam genericDisplay old command.

Specific Spot

Usually, a spotted character (C, I, E or A) is used for classes, interface, enum and abstract classes.

But you can define your own spot for a class when you define the stereotype, adding a single character and a color, like in this example:

@startuml

class System << (S,#FF7700) Singleton >>
class Date << (D,orchid) >>
@enduml

Packages

You can define a package using the package keyword, and optionally declare a background color for your package (Using a html color code or name).

Note that package definitions can be nested.

@startuml

package "Classic Collections" #DDDDDD {
  Object <|-- ArrayList
}

package com.plantuml {
  Object <|-- Demo1
  Demo1 *- Demo2
}

@enduml

Packages style

There are different styles available for packages.

You can specify them either by setting a default style with the command : skinparam packageStyle, or by using a stereotype on the package:

@startuml
scale 750 width
package foo1 <> {
  class Class1
}

package foo2 <> {
  class Class2
}

package foo3 <> {
  class Class3
}

package foo4 <> {
  class Class4
}

package foo5 <> {
  class Class5
}

package foo6 <> {
  class Class6
}

@enduml

You can also define links between packages, like in the following example:

@startuml

skinparam packageStyle rectangle

package foo1.foo2 {
}

package foo1.foo2.foo3 {
  class Object
}

foo1.foo2 +-- foo1.foo2.foo3

@enduml

Namespaces

Starting with version 1.2023.2 (which is online as a beta), PlantUML handles differently namespaces and packages.

There won’t be any difference between namespaces and packages anymore: both keywords are now synonymous.

Automatic package creation

You can define another separator (other than the dot) using the command : set separator ???.

@startuml

set separator ::
class X1::X2::foo {
  some info
}

@enduml

You can disable automatic namespace creation using the command set separator none.

@startuml

set separator none
class X1.X2.foo {
  some info
}

@enduml

Lollipop interface

You can also define lollipops interface on classes, using the following syntax: * bar ()- foo * bar ()-- foo * foo -() bar

@startuml
class foo
bar ()- foo
@enduml

Changing arrows orientation

By default, links between classes have two dashes -- and are vertically oriented. It is possible to use horizontal link by putting a single dash (or dot) like this:

@startuml
Room o- Student
Room *-- Chair
@enduml

You can also change directions by reversing the link:

@startuml
Student -o Room
Chair --* Room
@enduml

It is also possible to change arrow direction by adding left, right, up or down keywords inside the arrow:

@startuml
foo -left-> dummyLeft
foo -right-> dummyRight
foo -up-> dummyUp
foo -down-> dummyDown
@enduml

You can shorten the arrow by using only the first character of the direction (for example, -d- instead of -down-) or the two first characters (-do-).

Please note that you should not abuse this functionality : Graphviz gives usually good results without tweaking.

And with the link::use-case-diagram#d551e48d272b2b07[left to right direction] parameter:

@startuml
left to right direction
foo -left-> dummyLeft
foo -right-> dummyRight
foo -up-> dummyUp
foo -down-> dummyDown
@enduml

Association classes

You can define association class after that a relation has been defined between two classes, like in this example:

@startuml
class Student {
  Name
}
Student "0..*" - "1..*" Course
(Student, Course) .. Enrollment

class Enrollment {
  drop()
  cancel()
}
@enduml

You can define it in another direction:

@startuml
class Student {
  Name
}
Student "0..*" -- "1..*" Course
(Student, Course) . Enrollment

class Enrollment {
  drop()
  cancel()
}
@enduml

Association on same class

@startuml
class Station {
    +name: string
}

class StationCrossing {
    +cost: TimeInterval
}

<> diamond

StationCrossing . diamond
diamond - "from 0..*" Station
diamond - "to 0..* " Station
@enduml

[Ref. Incubation: Associations]

Skinparam

You can use the link::skinparam[skinparam] command to change colors and fonts for the drawing.

You can use this command : * In the diagram definition, like any other commands, * In an link::preprocessing[included file], * In a configuration file, provided in the link::command-line[command line] or the link::ant-task[ANT task].

@startuml

skinparam class {
BackgroundColor PaleGreen
ArrowColor SeaGreen
BorderColor SpringGreen
}
skinparam stereotypeCBackgroundColor YellowGreen

Class01 "1" *-- "many" Class02 : contains

Class03 o-- Class04 : aggregation

@enduml

Skinned Stereotypes

You can define specific color and fonts for stereotyped classes.

@startuml

skinparam class {
BackgroundColor PaleGreen
ArrowColor SeaGreen
BorderColor SpringGreen
BackgroundColor<> Wheat
BorderColor<> Tomato
}
skinparam stereotypeCBackgroundColor YellowGreen
skinparam stereotypeCBackgroundColor<< Foo >> DimGray

Class01 <>
Class03 <>
Class01 "1" *-- "many" Class02 : contains

Class03 o-- Class04 : aggregation

@enduml

Color gradient

You can declare individual colors for classes, notes etc using the # notation.

You can use standard color names or RGB codes in various notations, see link::color[Colors].

You can also use color gradient for background colors, with the following syntax: two colors names separated either by: * |, * /, * \, or * - depending on the direction of the gradient.

For example:

@startuml

skinparam backgroundcolor AntiqueWhite/Gold
skinparam classBackgroundColor Wheat|CornflowerBlue

class Foo #red-green
note left of Foo #blue\9932CC
  this is my
  note on this class
end note

package example #GreenYellow/LightGoldenRodYellow {
  class Dummy
}

@enduml

Help on layout

Sometimes, the default layout is not perfect…​

You can use together keyword to group some classes together : the layout engine will try to group them (as if they were in the same package).

You can also use hidden links to force the layout.

@startuml

class Bar1
class Bar2
together {
  class Together1
  class Together2
  class Together3
}
Together1 - Together2
Together2 - Together3
Together2 -[hidden]--> Bar1
Bar1 -[hidden]> Bar2


@enduml

Splitting large files

Sometimes, you will get some very large image files.

You can use the page (hpages)x(vpages) command to split the generated image into several files :

hpages is a number that indicated the number of horizontal pages, and vpages is a number that indicated the number of vertical pages.

You can also use some specific skinparam settings to put borders on splitted pages (see example).

@startuml
' Split into 4 pages
page 2x2
skinparam pageMargin 10
skinparam pageExternalColor gray
skinparam pageBorderColor black

class BaseClass

namespace net.dummy #DDDDDD {
    .BaseClass <|-- Person
    Meeting o-- Person

    .BaseClass <|- Meeting

}

namespace net.foo {
  net.dummy.Person  <|- Person
  .BaseClass <|-- Person

  net.dummy.Meeting o-- Person
}

BaseClass <|-- net.unused.Person
@enduml

Extends and implements

It is also possible to use extends and implements keywords.

@startuml
class ArrayList implements List
class ArrayList extends AbstractList
@enduml

Bracketed relations (linking or arrow) style

Line style

It’s also possible to have explicitly bold, dashed, dotted, hidden or plain relation, links or arrows:

  • without label

@startuml
title Bracketed line style without label
class foo
class bar
bar1 : [bold]
bar2 : [dashed]
bar3 : [dotted]
bar4 : [hidden]
bar5 : [plain]

foo --> bar
foo -[bold]-> bar1
foo -[dashed]-> bar2
foo -[dotted]-> bar3
foo -[hidden]-> bar4
foo -[plain]-> bar5
@enduml

  • with label

@startuml
title Bracketed line style with label
class foo
class bar
bar1 : [bold]
bar2 : [dashed]
bar3 : [dotted]
bar4 : [hidden]
bar5 : [plain]

foo --> bar          : ∅
foo -[bold]-> bar1   : [bold]
foo -[dashed]-> bar2 : [dashed]
foo -[dotted]-> bar3 : [dotted]
foo -[hidden]-> bar4 : [hidden]
foo -[plain]-> bar5  : [plain]

@enduml

[Adapted from QA-4181]

Line color

@startuml
title Bracketed line color
class foo
class bar
bar1 : [#red]
bar2 : [#green]
bar3 : [#blue]

foo --> bar
foo -[#red]-> bar1     : [#red]
foo -[#green]-> bar2   : [#green]
foo -[#blue]-> bar3    : [#blue]
'foo -[#blue;#yellow;#green]-> bar4
@enduml

Line thickness

@startuml
title Bracketed line thickness
class foo
class bar
bar1 : [thickness=1]
bar2 : [thickness=2]
bar3 : [thickness=4]
bar4 : [thickness=8]
bar5 : [thickness=16]

foo --> bar                 : ∅
foo -[thickness=1]-> bar1   : [1]
foo -[thickness=2]-> bar2   : [2]
foo -[thickness=4]-> bar3   : [4]
foo -[thickness=8]-> bar4   : [8]
foo -[thickness=16]-> bar5  : [16]

@enduml

[Ref. QA-4949]

Mix

@startuml
title Bracketed line style mix
class foo
class bar
bar1 : [#red,thickness=1]
bar2 : [#red,dashed,thickness=2]
bar3 : [#green,dashed,thickness=4]
bar4 : [#blue,dotted,thickness=8]
bar5 : [#blue,plain,thickness=16]

foo --> bar                             : ∅
foo -[#red,thickness=1]-> bar1          : [#red,1]
foo -[#red,dashed,thickness=2]-> bar2   : [#red,dashed,2]
foo -[#green,dashed,thickness=4]-> bar3 : [#green,dashed,4]
foo -[#blue,dotted,thickness=8]-> bar4  : [blue,dotted,8]
foo -[#blue,plain,thickness=16]-> bar5  : [blue,plain,16]
@enduml

Change relation (linking or arrow) color and style (inline style)

You can change the link::color[color] or style of individual relation or arrows using the inline following notation:

  • #color;line.[bold|dashed|dotted];text:color

@startuml
class foo
foo --> bar : normal
foo --> bar1 #line:red;line.bold;text:red  : red bold
foo --> bar2 #green;line.dashed;text:green : green dashed
foo --> bar3 #blue;line.dotted;text:blue   : blue dotted
@enduml

[See similar feature on link::deployment-diagram#0b2e57c3d4eafdda[deployment]]

Change class color and style (inline style)

You can change the link::color[color] or style of individual class using the two following notations:

  • #color ##[style]color

With background color first (#color), then line style and line color (##[style]color )

@startuml
abstract   abstract
annotation annotation #pink ##[bold]red
class      class      #palegreen ##[dashed]green
interface  interface  #aliceblue ##[dotted]blue
@enduml

[Ref. QA-1487]

  • #[color|back:color];header:color;line:color;line.[bold|dashed|dotted];text:color

@startuml
abstract   abstract
annotation annotation #pink;line:red;line.bold;text:red
class      class      #palegreen;line:green;line.dashed;text:green
interface  interface  #aliceblue;line:blue;line.dotted;text:blue
@enduml

First original example:

@startuml
class bar #line:green;back:lightblue
class bar2 #lightblue;line:green

class Foo1 #back:red;line:00FFFF
class FooDashed #line.dashed:blue
class FooDotted #line.dotted:blue
class FooBold #line.bold
class Demo1 #back:lightgreen|yellow;header:blue/red
@enduml

[Ref. QA-3770]

Arrows from/to class members

@startuml
class Foo {
+ field1
+ field2
}

class Bar {
+ field3
+ field4
}

Foo::field1 --> Bar::field3 : foo
Foo::field2 --> Bar::field4 : bar
@enduml

[Ref. QA-3636]

@startuml
left to right direction

class User {
  id : INTEGER
  ..
  other_id : INTEGER
}

class Email {
  id : INTEGER
  ..
  user_id : INTEGER
  address : INTEGER
}

User::id *-- Email::user_id
@enduml

[Ref. QA-5261]

Grouping inheritance arrow heads

You can merge all arrow heads using the skinparam groupInheritance, with a threshold as parameter.

GroupInheritance 1 (no grouping)

@startuml
skinparam groupInheritance 1

A1 <|-- B1

A2 <|-- B2
A2 <|-- C2

A3 <|-- B3
A3 <|-- C3
A3 <|-- D3

A4 <|-- B4
A4 <|-- C4
A4 <|-- D4
A4 <|-- E4
@enduml

GroupInheritance 2 (grouping from 2)

@startuml
skinparam groupInheritance 2

A1 <|-- B1

A2 <|-- B2
A2 <|-- C2

A3 <|-- B3
A3 <|-- C3
A3 <|-- D3

A4 <|-- B4
A4 <|-- C4
A4 <|-- D4
A4 <|-- E4
@enduml

GroupInheritance 3 (grouping only from 3)

@startuml
skinparam groupInheritance 3

A1 <|-- B1

A2 <|-- B2
A2 <|-- C2

A3 <|-- B3
A3 <|-- C3
A3 <|-- D3

A4 <|-- B4
A4 <|-- C4
A4 <|-- D4
A4 <|-- E4
@enduml

GroupInheritance 4 (grouping only from 4)

@startuml
skinparam groupInheritance 4

A1 <|-- B1

A2 <|-- B2
A2 <|-- C2

A3 <|-- B3
A3 <|-- C3
A3 <|-- D3

A4 <|-- B4
A4 <|-- C4
A4 <|-- D4
A4 <|-- E4
@enduml

[Ref. QA-3193, and Defect QA-13532]

Display JSON Data on Class or Object diagram

Simple example

@startuml
class Class
object Object
json JSON {
   "fruit":"Apple",
   "size":"Large",
   "color": ["Red", "Green"]
}
@enduml

[Ref. QA-15481]

For another example, see on link::json#jinnkhaa7d65l0fkhfec[JSON page].