Help with enums in Java
Is it possible to have an enum change its value (from inside itself)? Maybe开发者_C百科 it's easier to understand what I mean with code:
enum Rate {
VeryBad(1),
Bad(2),
Average(3),
Good(4),
Excellent(5);
private int rate;
private Rate(int rate) {
this.rate = rate;
}
public void increateRating() {
//is it possible to make the enum variable increase?
//this is, if right now this enum has as value Average, after calling this
//method to have it change to Good?
}
}
This is want I wanna achieve:
Rate rate = Rate.Average;
System.out.println(rate); //prints Average;
rate.increaseRating();
System.out.println(rate); //prints Good
Thanks
Yes. You could simply call
rate = Rate.Good;
for this specific case. But what I think you are really looking for is a successor function.
Here you are:
public class EnumTest extends TestCase {
private enum X {
A, B, C;
public X successor() {
return values()[(ordinal() + 1) % values().length];
}
};
public void testSuccessor() throws Exception {
assertEquals(X.B, X.A.successor());
assertEquals(X.C, X.B.successor());
assertEquals(X.A, X.C.successor());
}
}
Do you want something like this?
class Rate {
private static enum RateValue {
VeryBad(1),
Bad(2),
Average(3),
Good(4),
Excellent(5);
private int rate;
public RateValue(int rate) {
this.rate = rate;
}
public RateValue nextRating() {
switch (this) { /* ... */ }
}
}
private RateValue value;
public void increaseRating() {
value = value.nextRating();
}
}
The example in the question tries to change the value of "rate" by calling a method on it. This is impossible, enum values are objects, so you cannot change them for the same reasons you cannot assign a new value to "this". The closest thing you can do is add a method that returns another enum value, as proposed by Carl Manaster.
It should be possible but I have to admit that I've never tried it. In the end enums are just objects with a little twist so you should be able to do that unless you define the rate field as final.
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