How do I make this if-else block accept the enum types in Java?

[Jessaurum]

public class Undergrad{
......
public enum LetterGrade {
EPURE, DPURE, DPLUS, CMINUS, CPURE, CPLUS, BMINUS, BPURE, BPLUS, AMINUS, APURE
}
.....
public float getGPA(){
int totalCredit = getTotalCredits();
LetterGrade gradeValue;
float totalGradeValue;
float creditAmount;
float totalGrades;
int counter;
while (counter < credits.size()){
gradeValue = (LetterGrade)grades.get(counter);
creditAmount = ((Integer)credits.get(counter)).floatVal…
if((LetterGrade)gradeValue == EPURE){
totalGradeValue = 0;
}
.......else.....}

This isn't my whole code, I put "...." where I left out stuff. An example of a compiler complaint is:
Undergrad.java:72: cannot find symbol
symbol : variable EPURE
location: class Undergrad
if((LetterGrade)gradeValue == EPURE){
(error pointing to EPURE)

I've tried everything, I don't know what I'm doing wrong. :/

[masijade]

LetterGrade.EPURE