What's the difference between these two java variable declarations?

Question

public class SomeClass {
    private HashSet contents = new HashSet();
    private Set contents2 = new HashSet&         


        

Answer 1

One thing worth to mention, is that interface vs. concrete class rule is most important for types exposed in API, eg. method parameter or return type. For private fields and variables it only ensures you aren't using any methods from concrete implementation (i.e. HashSet), but then it's private, so doesn't really matter.

Another thing is that adding another type reference will slightly increase size of your compiled class. Most people won't care, but these things adds up.