Behaviour of hashCode(), equals() while working with maintaining uniqueness of user defined object in Set?

Question

While working on application where I want to discard duplicate entries for my value object (user defined VO), I used Set data structure by overriding hashCode(), equals() method.

I tried few iteration, it works fine but thing here I want to understand how uniqueness actually maintained? Is old object get replaced with new one or simply new one get ignore?

As they are identical how can I check above?

Thanks

possible duplicate of [Does adding a duplicate value to a HashSet/HashMap replace the previous value](http://stackoverflow.com/questions/12940663/does-adding-a-duplicate-value-to-a-hashset-hashmap-replace-the-previous-value) — Tim Biegeleisen, Aug 13 '15 at 04:19
In the case of `HashSet` the new value does not get inserted. — Tim Biegeleisen, Aug 13 '15 at 04:20
@kailanjian it's a valid question in order to understand what is happening under the hood. — Pumphouse, Aug 13 '15 at 04:31
Read the code : http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/HashSet.java — Amir Afghani, Aug 13 '15 at 04:50
@kailanjian They may *compare* exactly the same under `equals()` without being identical in all respects. — user207421, Aug 13 '15 at 07:12

score 0 · Accepted Answer · answered Aug 18 '15 at 06:55

According to the javadoc: [Set.add()] Adds the specified element to this set if it is not already present. If this set already contains the element, the call leaves the set unchanged and returns false. So answer your question "Is old object get replaced with new one or simply new one get ignore?" is new one get ignore

Behaviour of hashCode(), equals() while working with maintaining uniqueness of user defined object in Set?

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