The issue is with the string comparison using == instead of equals. == compares the references, which are very unlikely to be equal. Change to

if(grade.equals("A")){ totalGradePoints += 4; numClasses++; }else if(grade.equals("B")){ ... and it should work. See this answer for a detailed explanation.

As a good practice it is advisable to always use the static string as the object for calling equals on to prevent a NPE:

if("A".equals(grade)){ totalGradePoints += 4; numClasses++; }else if("B".equals(grade)){ ... If you are using Java 7, you can also do a switch statement with strings (though this one will throw an NPE if grade is null):

switch(grade) { case "A": totalGradePoints += 2; numClasses++; break; case "B": ... } And finally, since you are converting only one letter to an integer, to best solution is to convert them to char and for the values between A and D to do totalGradePoints += ('D' - grade.charAt(1)) + 1. So something along those lines would be simplest to read IMO:

while (true) {
final String input = in.next(); if(input == null || input.isEmpty()) break;

final char grade = input.charAt(0);
if(grade >= 'A' && grade <= 'D') {
    totalGradePoints += ('D' - grade) + 1;
} else if(grade == 'F') {
    // no gradepoints for 'F'
} else {
    break;
} //end if - else-if - else statement

++numClasses;

} //end while loop

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