When does a set allow duplication?

Question

So this is more of a “trying to understand” question than a question of “I need a solution.” For the assignment, we asked to create a list of products with itemNumberand price, but only one of them, so there is no item with the same itemNumber. I decided that I could create a set and get rid of the problem with duplicates. But if I add producta1, 4.99 and a productb1, 2.99, both products will be added.

Does this mean that the kit determines that these products are different from each other, they have different prices and therefore can be added to the kit?

Answer 1

, java.util.Set. java equals . equals , (Product), , , .

https://docs.oracle.com/javase/7/docs/api/java/util/Set.html

: 911DidBush , , equals, hashCode, hashCode.
Java:

, hashCode , , hashCode, , -.

http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html

Answer 2

Set javadoc:

, . e1 e2 , e1.equals(e2) .

, , , equals. , equals hashcode, , equals javadoc.