I'd like to know if calling a method from a different class is considered a relationship on a class diagram.
Regards.
Not always. Some types of relationships (e.g. a uses b, a notifies b, etc) can be implemented or supported by calling of an object's method thoough.
It depends on how closely the class diagram represents relationships. That is a design choice.
Related
I have class Controller in my java project, which has method like this:
As you can see, in the first line I am getting Singleton instance of ActualModes class and call method getActualModes().
So the first question is, which relatinship I should use in class diagram.
After that I am creating new instane of ModeContext class and then call method executeStrategy. In this case, which relatiship is better ?
It should be like this:
Access to the singleton (note the stereotype which is just convenient and no obligation or general standard) is anonymous and so you just have a dependency. The ModeContext in contrast uses a private (I don't know the scoping rules of the language you used, so I made it pivate) property called context. Note the dot which is saying exactly that.
Disclaimer: UML does not specify a mapping between Java and UML, so every answer to your question is open for debate.
I think both relationships are dependencies, drawn as dashed arrows from Controller to ActualModes and from Controller to ModeContext. The definition of 'dependency' according to the UML 2.5 specification (§7.8.4.1) is:
A Dependency is a Relationship that signifies that a single model Element or a set of model Elements requires other
model Elements for their specification or implementation.
An example of a type of relationship which is in my opinion less suited, is the association, although its definition (§11.5) is quite broad:
An Association classifies a set of tuples representing links between typed instances. (...) An Association specifies a semantic relationship that can occur between typed instances.
One could argue that there are links between Controller and the other two classes, in the form of variables, but these variables are local method variables, which exist only temporarily during the execution of the method. Associations represent more durable links, e.g. class members - as far as I understand UML and as far as I have seen associations used in practice.
In a UML class diagram, is it technically correct to have two possible compistion relationships leading to one class?
I.E. I have an inventory class, which has a composition of the inventory class. I want to have the same relationship but with a container class taking the place of the inventory.
So, can I have two compositions, or do I need to turn these into aggregations?
You can have as many composite associations as you like on the class level. But each instance can only be part of one composition at a specific moment in time.
UML superstructure says:
If the whole has aggregationKind = composite then the part can be included in at most one composite at a time
This article I wrote tries to explain the difference: UML Composition vs Aggregation vs Association
Any number of composition association can lead to one class of course. If instance of composed class is composed of instances of more types for example.
This my UML class diagram (URL)
In above diagram, ChildParent (or Child1, Child2, and Child3) can only be initialized in MainObject->create_new_object() and store it in class Library through ObjectData->lib->add_object(key, newObject).
So, how to define UML class relationship between ChildParent, Library, and MainObject?
Thank you
Relationships between classes are structural, not behavioral. The MainObject is creating it, but it is not controlling its lifespan nor does it own it in any way. After creating is it handed over to the ObjectData, transported to the Library and stored there. There is a behavioral relationship between the MainObject and the ChildParent object, but there is not a structural relationship between the two of them. I should not depict any relationship between them.
The Library is storing it. This is a typical whole part relationship and structural. What is a library without books? Therefor would I make use of the aggregation type of relation. It is not the composition, because the Library does not control the lifespan of any ChildParent or Child object nor does it imply that the ChildObject will be destroyed when the Library object is destroyed. That might happen, but given the presented data is that not clear to me.
EDIT as a reply to a comment:
Class diagrams show the structural relationships between classes, not their usage. When a class implements an interface, then will you see that relationship in the diagram. In the code (the behaviour) might you not see this relationship, because the implementation is hidden in a factory method or provided by a IoC container or it might even be a relationship that is never used.
What is the relationship between a class (the caller) that is picking a class (the callee) from a library and between the caller and the library?
It is obvious that the caller and the library have a behavioral relationship. If the module changes, can the caller get his callee from some other class. Therefor will the library and the caller have no relationship in the class diagram.
There is a structural relationship between the caller and the callee. The caller needs the callee. Your comment does not specify the exact relationship between them, but there is a relationship. The weakest form is the dependency relationship. An example in connection with a library is that a person is lending a book from a library. When he starts to read the book, is the callee used. It does not belong intrinsically to the person as a whole, but it does belong to a certain method of the person class.
There are a lot of ways to implement a library. It can be for instance a wardrobe. What is the relationship between a person in the military and his uniforms? He needs to wear some uniforms in certain situations, yet in other situations are those uniforms forbidden to wear. Wearing an uniform is a part of the class military. You can not be in the military without wearing an uniform in the time of duty. The moment you are out of the military are you not allowed to wear the uniform anymore. Hence has a military a compositional relationship with that uniform from his wardrobe.
There are more types of relationships possible between the caller and the callee. You can not say it at forehand. You must answer it the same way as any other relationship. The first question is very clear: is this a structural relationship or not? Keywords like 'is a' and 'has a' depict a structural relationship. Keywords like 'uses', 'asks', 'picks from' show a behavioral relationship. Have you concluded that it is a structural relationship, then should you find out what the dependency between the two classes is.
How do i model a call to a static method in a class diagram ? Can someone show me a link to a class diagram that has done that?
for example there's a class called Animal. and i have another class called Vertibrates, and it has a method which is static (and this is the only method in that class). My Animal class will be using this static method of the class Vertibrate. Therefore how can i model it in class diagram ?
You don't. Well, not in a class diagram at least. Instead, you should use sequence chart diagrams to express method calls (whether static or dynamic).
You can't model the call directly in a class diagram (as #Imontrieux says), but you can model the relationship (i.e., that Animal uses (calls) static methods in Vertibrate; BTW, the correct spelling is Vertebrate), which I suspect is actually what you meant.
You use a UML dependency for this, not an association (since the latter are for associations between instances of the classes at each end)--- see How to show usage of static methods UML Classdiagram.
Great question. One thing the GoF do in Design Patterns is used notes to demonstrate intended uses. For example, from the section on the Command Pattern:
Command Pattern
While #user1315906 is technically correct that you don't model such things in Class Diagrams, but rather in Use Case or Sequence Diagrams, if it makes sense to note how something is intended to be used in a Class Diagram, you can use a note :)
In a UML diagram when you create an instance of a subclass do you usually include the implicit construction of the superclass prior to the sub class constructor?
I usually wouldn't include it. The purpose of the UML sequence diagram is to show what happens between components. It shouldn't be read isolated from other parts of a design, so if a reader is unsure about what any of the components is (i.e. an instance of the subclass and the superclass), he or she should look into the - hopefully - accompanying class diagram.
sequence just shows the sequence of the logic of the module in question. Do you feel there is need to identify which method is truly being called? Also I would guess that the purpose of having a parent clas have a reference to a subclass is that until runtime you won't know which subclass is actually being referred to. If this is not the case, then should the concrete subclass be referred to explictly? does the method being called whether on the subclass or parent class alter the sequence in some way?