Java Math.random returning 0?

Question

I know this question has been answered before, and I have looked here: math.random, only generating a 0? as well as a few other forums, but thus far have been unable to answer my question.

I am trying to produce a random number between 1 and 3 (this includes 1 & 3) for a Rock Paper Scissors game. Unfortunately, the output for my random number is always 0.

Please be aware that I am not allowed to use the Random(); class, and must use the Math.random method to achieve this. Here is my code for Random number:

  public static int randomComputerChoice(int highVal, int lowVal) {
         do{
             highVal = 4;
             lowVal = 0;
     computerChoice=0;//resets random number
   //generates and returns a random number within user's range 
     computerChoice = (int)((Math.random()* highVal)+1);
     } while((computerChoice>= highVal)||(computerChoice<= lowVal));
     return (computerChoice);
} 

}

I wasn't sure if this was necessary, but I feel like the error could be in the rest of my code.

import java.util.Scanner;
import java.io.IOException;

public class RockPaperScissors {

    static int weaponChoice;
    static int computerChoice;
   static int lowVal = 1;
   static int highVal = 3;

    /**
     * @param args the command line arguments
     * @throws java.io.IOException
     */
    public static void main(String[] args) throws IOException {
        Scanner userInput = new Scanner(System.in);
        System.out.println(" =========================");
        System.out.println("====ROCK=PAPER=SCISSORS====");
        System.out.println(" =========================");
        int playAgain = 1; //sets a play again function
       do {
            System.out.println("Please select your weapon.");
            System.out.println("1 - Rock");
            System.out.println("2 - Paper");
            System.out.println("3 - Scissors");
            System.out.println("Choose wisely:");
            String choice = userInput.nextLine();
            weaponChoice = Integer.parseInt(choice);
            do {
           if (weaponChoice != 1 && weaponChoice != 2 && weaponChoice != 3) {
                    System.out.println("Please choose again, grasshopper. There are only"
                        + " three choices.");
                System.out.println("1 - Rock");
                System.out.println("2 - Paper");
                System.out.println("3 - Scissors");
                choice = userInput.nextLine();
                weaponChoice = Integer.parseInt(choice);
            }
            } while (weaponChoice != 1 && weaponChoice !=2 && weaponChoice != 3);

            if (weaponChoice == 1) {
                System.out.println("You have selected Rock as your weapon.");
            }
            else if (weaponChoice == 2) {
                System.out.println("You have selected Paper as your weapon.");
            }
            else {
                System.out.println("You have selected Scissors as your weapon.");
            }
            //Computer's Choice
             System.out.println("The computer's choice is "+computerChoice);


        } while (playAgain == 1);
}

   public static int randomComputerChoice(int highVal, int lowVal) {
         do{
             highVal = 4;
             lowVal = 0;
     computerChoice=0;//resets random number
   //generates and returns a random number within user's range 
     computerChoice = (int)((Math.random()* highVal)+1);
     } while((computerChoice>= highVal)||(computerChoice<= lowVal));
     return (computerChoice);
} 


} 

Thanks for any help! It is greatly appreciated.

Answer 1

Try: Min + (int)(Math.random() * ((Max - Min) + 1)) . Output should be a number between 1 and 3. Fill in 1 for min and 3 for max. That's it. The number range should be then: [1,3] which means that 1 AND 3 is included.

Here another proposal:

int number = 1 + (int)(Math.random() * ((3 - 1) + 1));
    System.out.println(number);
//alternative way:
// return number;