Question

我正在尝试使用do-while反转Integer数组中的每个数字，但出现NullPointerException错误。我正在尝试反转此数组中的每个元素：例如，如果这是我的数组：{12,34 ，56}，那么结果必须是：{21,43,65}。有人可以帮我吗？

public class Reverse {
  public int[] revCalculator(int[] number) {
    int[] reverse = null;
    for (int j = 0; j < number.length; j++) {
        do {
            reverse[j] = reverse[j] * 10 + number[j] % 10;
            number[j] /= 10;
        } while (number[j] > 0);
    }
    return reverse;
  }
}

public class ShowReverse {

  public static void main(String[] args) {

    // instantiation
    // -----------------------------------------
    Reverse rev = new Reverse();
    @SuppressWarnings("resource")
    Scanner in = new Scanner(System.in);


    System.out.println("Enter The Number Of Elements: ");
    int len = in.nextInt();
    int[] numbers = new int[len];


    for (int i = 0; i < len; i++) {
        System.out.println("Enter Number: ");
        numbers[i] = in.nextInt();
    }


    int[] result = rev.revCalculator(numbers);

    // shows the result
    // -----------------------------------------
    System.out.println("THE REVERSE WOULD BE: ");
    System.out.print(result);

  }
}

pic

Answer 1

您没有初始化变量reverseArray，像这样初始化它：

更新，我知道您要做什么，您想反转数组的值，而不是数组本身

public int[] revCalculator(int[] number) {
    int[] reverse = new int[number.length]; //Initialize it to the same size as the passed in arary
    //int[] reverse = null; //Problem
    StringBuilder sb = new StringBuilder();
    for (int j = 0; j < number.length; j++) 
    {
        //You could convert the number to string then reverse it and use parseInt() int
        reverse[j] = parseInt(sb.append(number[j].toString()).reverse().toString());
        //Clear the StringBuilder object
        sb.setLength(0);

    }
    return reverse;
}

Answer 2

我建议将反向数组初始化为与数字数组长度相同的数组。

int[] reverse = new int[number.length];

Answer 3

您需要进行一些更改：

初始化反向数组int[] reverse = new int[number.length];

System.out.print(result);将为您提供结果数组的地址。您必须显示数组的元素。

int[] result = new int[numbers.length];
result = rev.revCalculator(numbers);

// shows the result
// -----------------------------------------
System.out.println("THE REVERSE WOULD BE: ");
//System.out.print(result);
for(int i = 0 ; i<result.length; i++)
    System.out.println(result[i]);

希望这会有所帮助。

用Java反转数组中的每个数字的问题

3 个答案: