You never call your
setSumTotal
function except from the constructor with two arguments.
Either call that method from your
setDice1
and
setDice2
methods, or call it from the
rollDice
method.
public void rollDice() {
this.setDice1(random.nextInt(UPPER_DICE_ROLL_LIMIT)+1);
this.setDice2(random.nextInt(UPPER_DICE_ROLL_LIMIT)+1);
this.setSumTotal();
}