为什么要使用 declare an object reference variable static final？

Question

我正在阅读 Java 《如何编程》第 10 版并浏览了前几章。对于这个例子，我们展示了如何确保 SecureRandom class 但有一部分让我完全困惑。

// 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

书中提到它被声明为class、SecureRandom的private static final变量，这样一个对象总是被用来调用方法，rollDice().如果有一个程序包含 class Craps 的多个实例，它们将共享这个对象。我的问题是是否有可能需要 class SecureRandom 的多个实例？下一个问题是，既然是SecureRandom的对象引用变量，为什么还要调用Craps的变量？

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?

您的变量 randomNumbers 是 Craps class 的成员，类型为 SecureRandom。也就是说，它被定义为 Craps class 类型 SecureRandom 的变量。它被定义为静态意味着只有 randomNumbers 的一个副本并且它将被 Craps

的所有实例共享

为什么要使用 declare an object reference variable static final？

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

variables

object

static

secure-random