How to align blocks in PlantUML class diagrams?

Question

I am using PlantUML to make simple class diagrams and the tool is awesome, but I couldn't find any way to align classes with each other except putting them into packages or using relationships like Alice -left-* Bob. What I need is something like:

@startuml  
class Bob  
class Alice  
class Dan  
**Dan aligned Alice: horizontally**  
'or using a grid?  
**Bob at grid (2, 3)**  
@enduml

Is there a way?

Grube

Answer 1

Using a -[hidden] relation can do the job :

@startuml  
class Bob  
class Alice  
class Dan  
class Foo
class Bar
class Foobar

Bob -[hidden] Alice
Bar -[hidden] Foobar
@enduml

Downtoearth

Answer 2

UPDATES Aug.08.2019

From Rotsiser's comment, by combining changing the length of lines with together keyword, it can align elements

@startuml
class A
A ..> B
C ---> B
D ...> B
together {
    class E
    class F
    class G
}
E ----> B
@enduml

---

OUTDATED

You are able to align elements by changing the number of line's character, such as '-', '.', and so on.

@startuml
class A
A ..> B
C ---> B
D ...> B
E ----> B
F ----> B
G ----> B
@enduml

Resurrect

This will not align items, it will increase the length of the connector. Still helpful, but not exactly what I was looking for. – Grube

I had good results combining this with the other answer suggesting to use the together keyword. – Charade

Rotsiser's answer is correct, classes can be aligned with together keyword – Resurrect

Changing the line lenght also works when you need to add several arrows between the same two componnents in the same direction and need that each connection produce an arrow. Plantuml will create only one arrow by default. In my case I needed several arrows each with a different label – Donia

This approach won't work as soon as the classes are populated with different number of items – Maggy

Answer 3

Here is a solution.

The documentation: "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

To your question:

@startuml
class Bob
class Alice
class Dan
Alice -left[hidden]-> Bob
Alice -right[hidden]-> Dan 
@enduml

It may also be useful:

@startuml
class Bob
class Alice
class Dan
Bob -right-|> Alice
Alice -right-> Dan
interface Friend
Dan -up..> Friend
interface Person
Friend -left-> Person
interface Object
Person -down-> Object
interface Native
Object -right-> Native
@enduml

Computer

This approach won't work as soon as the classes are populated with different number of items – Maggy

It doesn't seem to work with objects – Replay

Answer 4

No, there's no way to do that, sorry :( The idea behind PlantUML is that you should not care too much about the layout rendering.

Actually, early versions of PlantUML use to align classes, but it was an issue: When there were many unrelated classes, diagrams tended to be very large and very thin. So a patch was added to organize classes in a square.

How many classes do you want to have in your diagram? Sure it would be possible to disable the organizing patch for e.g. 3 to 5 classes. You could post a suggestion to the forum to see what other users think about it.

Woodring

I thought about an alternative, that shouldn't be very hard to implement: add "group", which allows to group several objects in a same way "package" or "namespace" does (but there is no frame). This can have additional options like "horizontal" or "vertical", but it is not that important. Important is, that we should be able to group classes after the whole diagram is finished by simply adding 'group { Bob Alice Animals.Cat }' which will force classes to stay close to each other. – Grube

Answer 5

You don't need a hidden package, use the together keyword:

together {
class A
class B
}

Venlo

I had good results combining this with the other answer suggesting to change the number of lines in the arrow link. – Charade

Answer 6

A cleaner approach is to put them in a hidden package, which is more logical.

@startuml

skinparam shadowing false
skinparam package<<Layout>> {
  borderColor Transparent
  backgroundColor Transparent
  fontColor Transparent
  stereotypeFontColor Transparent
}

package x <<Layout>>{ 
    class A
    class B
} 
A .. D
B .. C
C .. D

A1 .. D1
B1 .. C1
C1 .. D1

@end

Balikpapan

This is not a response to @Yuriy Kulikov question : align more than two classes horizontaly. Nice theming anyway. – Downtoearth

: I thought this is what he wanted. Yuriy Kulikov . Settle this for us. :) @Downtoearth : Can you draw a diagram/sketch of expected output according to you? – Balikpapan

This approach won't work as soon as the classes are populated with different number of items. – Maggy