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copied!<p>Joshua Bloch in his excellent "Effective Java" book says that you should ALWAYS make defensive copies when returning something like this. That may be a little extreme, especially if the ContactDetails objects are not Cloneable, but it's always the safe way. If in doubt always favour code safety over performance - unless profiling has shown that the cloneing is a real performance bottleneck.</p> <p>There are actually several levels of protection you can add. You can simply return the member, which is essentially giving any other class access to the internals of your class. Very unsafe, but in fairness widely done. It will also cause you trouble later if you want to change the internals so that the ContactDetails are stored in a Set. You can return a newly-created list with references to the same objects in the internal list. This is safer - another class can't remove or add to the list, but it can modify the existing objects. Thirdly return a newly created list with copies of the ContactDetails objects. That's the safe way, but can be expensive.</p> <p><strong>I would do this a better way.</strong> Don't return a list at all - instead return <strong>an iterator over a list</strong>. That way you don't have to create a new list (List has a method to get an iterator) but the external class can't modify the list. It can still modify the items, unless you write your own iterator that clones the elements as needed. If you later switch to using another collection internally it can still return an iterator, so no external changes are needed.</p>

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