OOP throw two dice this.setSumTotal(); does not work

Just been experimenting with a class in which 2 dice are thrown and the total calculated. I am using OOP setting the total to this.dice1+this.dice2. However, when instantiating a Dice in another class the dice1 & dice2 throw work fine and generate 2 random numbers between 1 and 6. However, the sumTotal just defaults to 0 rather than adding dice1 and dice2.

Dice class:

public class Dice {

//create a random class
Random random = new Random(); 

//constants set the boundaries of possible dice roll values
private final static int UPPER_DICE_ROLL_LIMIT=6; 
private final static int LOWER_DICE_ROLL_LIMIT=1; 

//instance vars 
private int dice1; 
private int dice2;
private int sumTotal; 


/**
 * default constructor
 */
public Dice() {
}

/**
 * @param dice1
 * @param dice2
 * @param sumTotal
 */
public Dice(int dice1, int dice2) {
    this.setDice1(dice1);
    this.setDice2(dice2);
    this.setSumTotal();
} 

/**
 * @return the dice1
 */
public int getDice1() {
    return dice1;
}

/**
 * sets the number of dice1's roll - must be >=1 & <=6
 * @param dice1 the dice1 to set
 */
public void setDice1(int dice1) throws IllegalArgumentException {
    if (dice1>=LOWER_DICE_ROLL_LIMIT && dice1<=UPPER_DICE_ROLL_LIMIT) {
        this.dice1 = dice1;
    }else {
        throw new IllegalArgumentException("Invalid number"); 
    }
}

/**
 * @return the dice2
 */
public int getDice2() {
    return dice2;
}

/**
 * sets the number of dice2's roll - must be >=1 & <=6
 * @param dice2 the dice2 to set
 */
public void setDice2(int dice2) throws IllegalArgumentException {
    if (dice2>=LOWER_DICE_ROLL_LIMIT && dice2<=UPPER_DICE_ROLL_LIMIT) {
        this.dice2 = dice2;
    }else {
        throw new IllegalArgumentException("Invalid number"); 
    }this.dice2 = dice2;
} 

/**
 * @return the sumTotal
 */
public int getSumTotal() {
    return sumTotal;
}

/**
 * sets the total score of the two dice (dice1 + dice2)
 * @param sumTotal the sumTotal to set
 */
public void setSumTotal() {
    this.sumTotal = this.dice1 + this.dice2; 
}


/**
 * method to set randomly set the values of the dice rolls
 */
public void rollDice() {
    
    this.setDice1(random.nextInt(UPPER_DICE_ROLL_LIMIT)+1);
    this.setDice2(random.nextInt(UPPER_DICE_ROLL_LIMIT)+1); 
    
}

}

Game class:

public class Game {

public static void main(String[] args) {
    
    
    Dice dice = new Dice(); 
    
    dice.rollDice();
    
    System.out.println(dice.getDice1());
    System.out.println(dice.getDice2());
    System.out.println(dice.getSumTotal());

    }

}

Thanks in advance, Cameron