Java HotSpot Enum overhead

Question

Suppose you have a "simple" enum:

public enum Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
    THURSDAY, FRIDAY, SATURDAY 
}

And then you use it somewhere:

Day day = Day.SUNDAY;
...
if(day==Day.SUNDAY) {...}

How does this compare performance wise (memory and time) with using ints?

int day = Day.SUNDAY;
...
public class Day {
    public static final int SUNDAY=0;
    public static final int MONDAY=1;
}

We have the JIT HotSpot compiler enabled along with other "standard" optimization.

Answer 1

There may be a slight performance loss for the enum whenever you reference Day.SUNDAY, because the int constant is a compile-time constant and so can be inlined, whereas the enum constant requires a getstatic.

Comparing two ints or two references is of course identical in terms of time required, since you are comparing the references (addresses), not calling .equals().

Of course, the performance hit here is minuscule; the only reason to worry about this would be if this is in a performance-critical part of your application and profiling shows that using ints is better. The benefits of enums for maintainability and code correctness far outweigh a slight inefficiency like this.