Why doesn't java.util.HashSet have a get(Object o) method?

Question

I\'ve seen other questions about getting objects from Set\'s based on index value and I understand why that is not possible. But I haven\'t been able to find a

Answer 1

A Set is a Collection of objects which treats a.equals(b) == true as duplicates, so it doesn't make sense to try to get the same object you already have.

If you are trying to get(Object) from a collection, a Map is likely to be more appropriate.

What you should write is

Map map = new LinkedHashMap<>();

map.put("1", "Number 1");
map.put("2", null);
String description = map.get("1");

if an object is not in the set (based on equals), add it, if it is in the set (based on equals) give me the set's instance of that object

In the unlikely event you need this you can use a Map.

Map map = // LinkedHashMap or ConcurrentHashMap

Bar bar1 = new Bar(1);
map.put(bar1, bar1);

Bar bar1a = map.get(new Bar(1));