Composition in Cam's Book

[Brian Peasey]

Hi,

On page 140 of Cam's study guide(2nd Ed.)there's an example UML diagram of composition and then a written explanation of how it's implemented in Java, but no actual example in java. Could someone post an code example based on this UML diagram? Thanks. (I understand composition in at the UML level but need to see this particular example in actual Java syntax)

Brian

[Stephen Davies]

Well, UML is pretty near the implementation but here is my take on p140, in a very simple eample (the UML doesnt specify any access modifers or return types so I made all the methods default and the instance variable.

 
public class Exam {
 
 java.util.Vector<Question> questions;
 
 void addQuestions(){}
 void deleteQuestions(){}
 void updateQuestion(){}
 Question getQuestion(){}
 
 }
 
public class Question{
 
 String query;
 String answer;
 
}
 

The main pont I think here is just to show the UML representation of Composition. The code doesnt really show more than the basic Association and Navigation (the getQuestion() Method). To represent composition in the code the constructor for the Question class would need a reference to an exam object or something similar to show that the lifecycle of the question(s) is dependent on an exam object.
[ October 26, 2008: Message edited by: Stephen Davies ]