java独特元素的集合

Question

I have a Collection coll of myObject. I'd like to add an element to coll only if there is no such element in the collection.

I have overriden the equals method of myObject. It checks for the equality of its 20 attributes.

However in the case of the collection, I'd like to make the equality check (and hence the add) based only on one of these attributes.

Maybe my architecture is flawed, and I shouldn't have two definitions of equals, and should instead have 2 different objects.

However, is it possible, without too much refactoring, to achieve what I want from here ? That is to say, I'd like some sort of a Set collection, where I could tell how to make the comparison check. This would be similar to the Collection.sort() method, where you can provide the comparator to check for the comparison.

Answer 1

转到HashSet。它将存储唯一的值。从这里的注释中，你必须覆盖hashcode和equals方法以提供每个对象的唯一性。你可以在这里阅读这两种方法之间的关系。

Answer 2

您正在寻找Set和其中一个实现。

Answer 3

You cannot use the existing containers to enforce uniqueness here, because they all want to use equals .

If it is only one attribute, you could use a Map, with that attribute as a key. That will allow only one entry per value for that attribute.

equals and hashCode are intended to be used with Collections. You should change your design. Maybe call your own equals (the one you have now) something else. Maybe don't put these things into collections directly, but wrapped into an adapter of some sort.

Answer 4

By using a TreeSet(Comparator comparator) you don't need to rely on the 'equals/hashCode' implementation.

Similarly if your collection is a list you can sort it using a comparator Collections.sort(List list, Comparator c);