## Object Diagram



## Definition of objects

You define instances of objects using the ``object``
keyword.

<plantuml>
@startuml
object firstObject
object "My Second Object" as o2
@enduml
</plantuml>


## Relations between objects

Relations between objects are defined using the following symbols :

| Type        | Symbol   | Image              |
| ----------- | -------- | ------------------ |
| Extension   | ``<|--`` | ![](extends01.png) |
| Composition | ``*--``  | ![](sym03.png)     |
| Aggregation | ``o--``  | ![](sym01.png)     |

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

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

It is possible a 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.


<plantuml>
@startuml
object Object01
object Object02
object Object03
object Object04
object Object05
object Object06
object Object07
object Object08

Object01 <|-- Object02
Object03 *-- Object04
Object05 o-- "4" Object06
Object07 .. Object08 : some labels
@enduml
</plantuml>


## Associations objects

<plantuml>
@startuml
object o1
object o2
diamond dia
object o3

o1  --> dia
o2  --> dia
dia --> o3
@enduml
</plantuml>


## Adding fields

To declare fields, you can use the symbol ``:`` followed by
the field's name.

<plantuml>
@startuml

object user

user : name = "Dummy"
user : id = 123

@enduml
</plantuml>

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

<plantuml>
@startuml

object user {
  name = "Dummy"
  id = 123
}

@enduml
</plantuml>


## Common features with class diagrams

* [Hide attributes, methods...](class-diagram#Hide)
* [Defines notes](class-diagram#Notes)
* [Use packages](class-diagram#Using)
* [Skin the output](class-diagram#Skinparam)


## Map table or associative array

You can define a map table or [associative array](https://en.wikipedia.org/wiki/Associative_array), with `map` keyword and `=>` separator.
 
<plantuml>
@startuml
map CapitalCity {
 UK => London
 USA => Washington
 Germany => Berlin
}
@enduml
</plantuml>

<plantuml>
@startuml
map "Map **Contry => CapitalCity**" as CC {
 UK => London
 USA => Washington
 Germany => Berlin
}
@enduml
</plantuml>

<plantuml>
@startuml
map "map: Map<Integer, String>" as users {
 1 => Alice
 2 => Bob
 3 => Charlie
}
@enduml
</plantuml>


And add link with object.
<plantuml>
@startuml
object London

map CapitalCity {
 UK *-> London
 USA => Washington
 Germany => Berlin
}
@enduml
</plantuml>

<plantuml>
@startuml
object London
object Washington
object Berlin
object NewYork

map CapitalCity {
 UK *-> London
 USA *--> Washington
 Germany *---> Berlin
}

NewYork --> CapitalCity::USA
@enduml
</plantuml>

*[Ref. [#307](https://github.com/plantuml/plantuml/issues/307)]*