October 2003
Beginner
734 pages
16h 56m
English
Content preview from Head First EJB
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Multiplicity affects return type!
A Movie has one Director. When you call getDirector(), you get back one Director. So the return type of getDirector() is a Director().
But a Director has many movies, so when you call getMovies(), you get back a Collection of Movies.
Movie has a multiplicity of “many” in its relationship with Director. That does NOT mean that Movie has “many” Directors... it means that Director has “many” Movies!
So Director has a getMovies() that returns a Collection of Movies.
And Director has a multiplicity of “one”, which means that Movie will return just one Director.
In the Movie-to-Director relationship, the multiplicity of Movie is many and the multiplicity of Director is one.
A multiplicity of one means the object you’re related to holds just one of you.
Director has a multiplicity of one, so the Movie object related to Director returns just a single Director bean (OK, technically the component interface of Director, but you know what we mean by now).
A multiplicity of many means the object you’re related to holds a Collection of you.
Movie has a multiplicity of many, so the Director object related to Movie returns a Collection of Movie beans.
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