数组Java彩票类

Question

因此，我正在编写一个Lottery类和一个演示Lottery类的类。我已经完成了工作并编译了它，但当我运行它时

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4  
at LotteryDemo.main(LotteryDemo.java:21)

这是我的代码，任何帮助都将不胜感激

类：

    import java.util.Random;


import java.util.Scanner;

   public class Lottery
   {


  int NUM_DIGITS = 5;   
  int[] lotteryNumbers = new int[4];




  public Lottery(){
     Random rand = new Random();
     lotteryNumbers[0] = rand.nextInt(10);
     lotteryNumbers[1] = rand.nextInt(10);
     lotteryNumbers[2] = rand.nextInt(10);
     lotteryNumbers[3] = rand.nextInt(10);
     lotteryNumbers[4] = rand.nextInt(10);
     getLotteryNums();

  }


  public int numIntsInCommon(int[] picks){
     int inCommon = 0;

     for (int counter = 0; counter < 5; counter++)
     {
        for (int index = 0; index < 5; index++)
        {
           if (lotteryNumbers[counter] == picks[index])
              inCommon++;
           return inCommon;
        }
        return inCommon;
     }

     return inCommon;
  }

  public String getLotteryNums(){
     return lotteryNumbers[0] + ", " + lotteryNumbers[1] + ", " + 
                    lotteryNumbers[2] + ", " + lotteryNumbers[3] + ", " +
                    lotteryNumbers[4];
  }




}

The LotteryDemo类：

    import java.util.*;


   public class LotteryDemo
   {
  public static void main(String[] args)
  {

        Scanner input = new Scanner(System.in);
     int[] userNumbers = new int[4];

     System.out.println("Please supply your lottery picks. Choose unique numbers between 0 and 9.");
     System.out.print("Enter digit 1: ");
        userNumbers[0] = input.nextInt();
        System.out.print("Enter digit 2: ");
        userNumbers[1] = input.nextInt();
        System.out.print("Enter digit 3: ");
        userNumbers[2] = input.nextInt();
        System.out.print("Enter digit 4: ");
        userNumbers[3] = input.nextInt();
        System.out.print("Enter digit 5: ");
        userNumbers[4] = input.nextInt();


    Lottery lottery = new Lottery();


    System.out.print("Lottery Numbers: " + lottery.getLotteryNums());
  System.out.print("Number of matching digits: " + lottery.numIntsInCommon(userNumbers));
    if(lottery.numIntsInCommon(userNumbers) == 5)
        System.out.print("All 5 match! You have hit the jackpot!");
  }


}

Answer 1

int[] lotteryNumbers = new int[4];

这意味着数组有4个元素或lotteryNumbers[0]lotteryNumbers[3]

因此lotteryNumbers[4] = rand.nextInt(10);将导致上述异常

与userNumbers在main中类似，这导致了异常

int[] userNumbers = new int[4];
...
userNumbers[4] = input.nextInt(); // java.lang.ArrayIndexOutOfBoundsException

Answer 2

用new int[4]分配数组，这意味着它有4个编号为0到3的元素。 当您访问索引为4的元素时，它超出了范围

Answer 3

Java中的数组具有如下实例化：

type[] name = new type[size]
                       ^

大小表示数组中索引数。如您所知，数组从零开始，因此：

int[] userNumbers = new int[4]

生成一个数组：

[ ][ ][ ][ ]
 0  1  2  3

因此userNumbers[4]不存在。您需要为五个索引创建userNumber[5]