Why would you use declare an object reference variable static final?

Question

I am reading the Java How to Program 10th edition and going through the first few chapters. For this example, we are show how to make sure of the SecureRandom class but there is a part which totally puzzles me.

// Fig. 6.8: Craps.java
// Craps class simulates the dice game craps.
import java.security.SecureRandom;

public class Craps
{
    // create secure random number generator for use in method rollDice
    private static final SecureRandom randomNumbers = new SecureRandom();

    // enum type with constants that represent the game status
    private enum Status { CONTINUE, WON, LOST };

    // constants that represent common rolls of the dice
    private static final int SNAKE_EYES = 2;
    private static final int TREY = 3;
    private static final int SEVEN = 7;
    private static final int YO_LEVEN = 11;
    private static final int BOX_CARS = 12;

    // plays one game of craps
    public static void main(String[] args)
    {
        int myPoint = 0; // point if no win or loss on first roll
        Status gameStatus; // can contain CONTINUE, WON or LOST

        int sumOfDice = rollDice(); // first roll of the dice

        // determine game status and point based on first roll
        switch (sumOfDice)
        {
            case SEVEN: // win with 7 on first roll
            case YO_LEVEN: // win with 11 on first roll
                gameStatus = Status.WON;
                break;
            case SNAKE_EYES: // lose with 2 on first roll
            case TREY: // lose with 3 on first roll
            case BOX_CARS: // lose with 12 on first roll
                gameStatus = Status.LOST;
                break;
            default:
                gameStatus = Status.CONTINUE; // game is not over
                myPoint = sumOfDice; // remember the point
                System.out.printf("Point is %d%n", myPoint);
                break;
        }

        // while game is not complete
        while (gameStatus == Status.CONTINUE) // not WON or LOST
        {
            sumOfDice = rollDice(); // roll dice again

            // determine game status
            if (sumOfDice == myPoint) // win by making point
                gameStatus = Status.WON;
            else if (sumOfDice == SEVEN) // lose by rolling 7 before point
                gameStatus = Status.LOST;
        }

        // display won or lost message
        if (gameStatus == Status.WON)
            System.out.println("Player wins");
        else
            System.out.println("Player loses");
    }

    // roll dice, calculate sum and display results
    public static int rollDice()
    {
        // pick random die values
        int die1 = 1 + randomNumbers.nextInt(6); // first die roll
        int die2 = 1 + randomNumbers.nextInt(6); // second die roll

        int sum = die1 + die2; // sum of die values

        // display results of this roll
        System.out.printf("Player rolled %d + %d = %d%n", die1, die2, sum);

        return sum;
    }
} // end class Craps

From the book, it mentions that it is declared as private static final variable of the class, SecureRandom so that that one object is always being used to call method, rollDice(). If there were a program which contains multiple instance of class Craps, they will all share this one object. My question is will there be a chance whereby multiple instances of class SecureRandom will be needed? Next question will be since this is an object referenced variable of SecureRandom, why is it still called as a variable of Craps?

Answer 1

Next question will be since this is an object referenced variable of SecureRandom, why is it still called as a variable of Craps?

Your variable randomNumbers is a member of Craps class and it is of TYPE SecureRandom. i.e. it is defined to be used as variable of Craps class which is of type SecureRandom. It is defined as static means there will be only one copy of randomNumbers and it will be shared by all instances of Craps