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POEnsuring UML constraints in Java?
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copied!<p>Say that the design of my application is such that there are two classes: <code>Person</code> and <code>Company</code>. Also suppose I have defined a UML diagram that defines a one-to-many relationship between <code>Person</code> and <code>Company</code>: every <code>Person</code> object must belong to exactly one <code>Company</code>, and a <code>Company</code> can contain many <code>Person</code>s.</p> <p>What are some best practices for ensuring that this simple constraint always holds, i.e., that there is never a point in time where a <code>Person</code> object is contained in more than one <code>Company</code>? I've thought of three approaches:</p> <ol> <li><p>Have perfect, bug-free code that would <em>never</em> violate any of my constaints. However, being a realist, I know that this is difficult or impossible, especially as the number of constraints grows.</p></li> <li><p>Implement an <code>ensureCorrectness()</code> method that manually checks each and every constraint. In this example, it would loop through all <code>Person</code>s, and make sure that exactly one <code>Company</code> contained that <code>Person</code>. If not, it would print an error. I would call this method every so often.</p></li> <li><p>Use, e.g., Hibernate to define a database schema and store the data into a database. In the schema, I can define a constraint to match the constrains in my UML diagram. Then, whenever I persists data into the database, Hibernate will check all the constraints and print an error if something's gone wrong.</p></li> </ol> <p>But I can't help wondering if there is another, cleaner way to do this in Java, that doesn't rely on (1) perfection, (2) manual validation, or (3) a relational database. Is there a library or framework that would allow me to specify annotations in the code similar to:</p> <p><code> @OneToMany(Person, Company) </code></p> <p>Or perhaps more specifically:</p> <p><code> @OneToMany(Person, Company.persons) </code></p> <p>assuming the <code>Company</code> class had a <code>List<Person> persons</code> member variable.</p> <p>And if I wanted to ensure that a person's social security number is unique across all <code>Person</code>s, I could say:</p> <p><code> @Unique(Person.SSN) </code></p> <p><strong>Does anything like this exist for Java?</strong></p>

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