Question

我正在编写一个对象类来计算每个字母的数量，当我运行我的测试代码时，它会在“abc”传递时向我显示一个空指针异常。我无法弄清楚原因。测试代码没有错误，但我的对象类中有一些错误。

public class LetterInventory {

   private static final int COUNTER = 26;
   private int size = 0;
   private int[] inventory;

   public LetterInventory() {
    inventory = new int [COUNTER];
 }
   public LetterInventory (String data) {
      data = data.toLowerCase();
      for(int i = 0; i < data.length(); i++) {
         int charPosition = data.charAt(i) - 'a';
         if(charPosition >= 0 && charPosition <  COUNTER) {
             inventory[charPosition]++;
             size++;
         } 
      }
   }

Answer 1

您没有在第二个构造函数中初始化数组。

public LetterInventory(String data) {
    inventory = new int[COUNTER]; // <= initialization was missing
    data = data.toLowerCase();
    for (int i = 0; i < data.length(); i++) {
        int charPosition = data.charAt(i) - 'a';
        if (charPosition >= 0 && charPosition < COUNTER) {
            inventory[charPosition]++;
            size++;
        }
    }
}

Answer 2

我不允许发表评论，所以你去了：

public LetterInventory(String data) {
    this();
    //inventory = new int[COUNTER]; // <= initialization was missing

    data = data.toLowerCase();
    for (int i = 0; i < data.length(); i++) {
        int charPosition = data.charAt(i) - 'a';
        if (charPosition >= 0 && charPosition < COUNTER) {
        inventory[charPosition]++;
        size++;
    }
}

我该如何修复这个特定的空指针异常

2 个答案: