java - 如何修复java中随机数 boolean 数组的: Exception in thread "main" java. lang.ArrayIndexOutOfBoundsException

Question

这个问题已经有答案了:

What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it? (25 个回答)

已关闭 4 年前。

我正在编写一个程序，可以获取他们想要的随机数以及他们想要达到的最高数字，但是当我运行代码时，它没有给我他们要求的数字数量。它要么给我 1 个号码，要么没有。然后它说“线程“main”中出现异常 java.lang.ArrayIndexOutOfBoundsException: 9 在practice4.practice4.main(practice4.java:38)”处为红色​​。

double randomNum;
        int highestNumber, numsInLottery, display;
        boolean[] numberUsed;

        System.out.println("Welcome to the Lottery Number Generator!");

        System.out.println("How many numbers are in your lottery?");
        numsInLottery = TextIO.getInt();

        System.out.println("What is the highest possible number?");
        highestNumber = TextIO.getInt();


        numberUsed= new boolean [numsInLottery];

        for (int index = 0; index < numsInLottery; index++)
        {
        numberUsed [index]= false;

        while(index < highestNumber)
        {
            do
            {

                randomNum = Math.random() * highestNumber + 1;
                display = (int) randomNum ;

            } while (numberUsed [display - 1 ] ); 

        System.out.print(display + " ");
        numberUsed [display + 1] = true;

        }   
        }
        }   
        }

在我有numberUsed= new boolean [numsInLottery];之前我不小心把highestNumber 放在了numsInLottery 的位置。当我有了它时，它会给我所有的数字。但现在我已经改变了它，它不再起作用了这就是我现在得到的

Welcome to the Lottery Number Generator!
How many numbers are in your lottery?
6
What is the highest possible number?
? 30
1 Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 21
    at practice4.practice4.main(practice4.java:35)

Answer 1

在您的情况下，您似乎需要使用 boolean 数组来验证之前是否未生成过生成的数字，在这种情况下，这就是您需要的核心逻辑。

int[] lotteryNumbers = new int[numsInLottery];
boolean[] lotteryNumberHasBeenGenerated = new boolean[highestNumber];

for(int i=0;i<highestNumber;i++){ //none of the numbers have been generated at this point
    lotteryNumberHasBeenGenerated[i]=false;
}

for (int i = 0; i < numsInLottery; i++) {
    int random;
    do{
        random=((Double)(Math.random() * highestNumber)).intValue();
    }while(lotteryNumberHasBeenGenerated[random]);

    lotteryNumbers[i] = random;
    lotteryNumberHasBeenGenerated[random]=true; //the number is maked as generated

}

这将解决问题，最终的方法应该如下所示:

public void lottery() {

    System.out.println("Welcome to the Lottery Number Generator!");
    System.out.println("How many numbers are in your lottery?");
    int numsInLottery = TextIO.getInt();
    System.out.println("What is the highest possible number?");
    int highestNumber = TextIO.getInt();

    int[] lotteryNumbers = new int[numsInLottery];
    boolean[] lotteryNumberHasBeenGenerated = new boolean[highestNumber];

    for(int i=0;i<highestNumber;i++){ //none of the numbers have been   generated at this point
        lotteryNumberHasBeenGenerated[i]=false;
    }

    for (int i = 0; i < numsInLottery; i++) {
        int random;
        do{
            random=((Double)(Math.random() * highestNumber)).intValue();
        }while(lotteryNumberHasBeenGenerated[random]);

        lotteryNumbers[i] = random;
        lotteryNumberHasBeenGenerated[random]=true; //the number is maked as    generated

}

    System.out.println("Lottery numbers:\n" + Arrays.toString(lotteryNumbers));
}

尽管如果是这种情况，您将错过很多验证:S

Also, The problem you are having in the console logs is thrown in java when you try to access a position in the array that it does not have, for example if you created an array with size 5 and you are accessing the position number 9 or with index 8 Exception. Here is an explanation of how that works