UML sequence diagram, call

Question

Let's say we have three classes A, B and C, and an instance a (resp. b/c) of type A (resp. B/C). Suppose that b is an attribute of a and c is an attribute of b.

In a method of a, the following is called : b.c.operation()

How can we represent this in a sequence diagram ?

I don't know if I need to have 1) one arrow from a to c 2) one arrow from b to c 3) one arrow from a to b and one from b to c... — Friedrich, Dec 15 '17 at 08:22

score 4 · Accepted Answer · answered Dec 15 '17 at 08:40

According to the Law of Demeter, an object should only communicate directly with its own neighbours. So in your case, a should not be calling b.c.operation() at all, as c is not a's neighbour. Rather, class B should provide an interface for this purpose, such as doCOperation(){c.operation();} and this is what a should call.

So the sequence of operations beocomes:

a calls b.doCOperation()
b calls c.Operation() within doCOperation() and returns the result to a.

Have a go at the sequence diagram now and it should be much easier.

I never knew that this is called LoD (after doing that stuff for >30 years), but only under the term "information hiding". — qwerty_so, Dec 15 '17 at 15:24

score 1 · Answer 2 · answered Dec 29 '17 at 21:55

1

In programming it is not good to have b.c.operation()

All data should be hidden (should be private) in the class.

But if we have b.c.operation() , in the compiler it changes to (b.c).operation() so your code is equal to this code:

t=b.c;
t.operation();

answered Dec 29 '17 at 21:55

the compiler changes it? or at Runtime? – Gholamali Irani Dec 29 '17 at 23:15
absolutely compiler. – Dec 30 '17 at 13:26

score 1 · Answer 3 · answered Jan 07 '18 at 08:55

1

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answered Jan 07 '18 at 08:55

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UML sequence diagram, call

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