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How does a TreeSet, HashSet or LinkedHashSet behave when the objects are mutable? I cannot imagine that they would work in any sense?
If I modify an object after I have added it; what is the behaviour of the list?
Is there a better option for dealing with a collection of mutable objects (which I need to sort/index/etc) other than a linked list or an array and simply iterating through them each time?
The
Setinterface addresses this issue directly: “Note: Great care must be exercised if mutable objects are used as set elements. The behavior of a set is not specified if the value of an object is changed in a manner that affects equals comparisons while the object is an element in the set. A special case of this prohibition is that it is not permissible for a set to contain itself as an element.”Addendum:
When trying to decide which collection implementation is most suitable, it may be worth looking over the core collection interfaces. For
Setimplementations in particular, as long asequals()andhashCode()are implemented correctly, any unrelated attributes may be mutable. By analogy with a database relation, any attribute may change, but the primary key must be inviolate.