读取文件字符串时charAt(1)抛出字符串过短异常的问题求助

使用charAt()函数获取文件读取字符串的第一个和第二个字符时，执行charAt(0)正常，但charAt(1)抛出字符串过短异常，确认字符串长度足够。代码如下：

while(inputFile.hasNext()){
    //read file first line
    String line = inputFile.nextLine();
    //if the first 2 letters of the line the scanner is reading are the same
    //as the search letters print the line and add one to the linesPrinted count
    String lineOne = String.valueOf(line.charAt(0));
    String lineTwo = String.valueOf(line.charAt(1));
    String searchOne = String.valueOf(search.charAt(0));
    String searchTwo = String.valueOf(search.charAt(1));

    if (lineOne.compareToIgnoreCase(searchOne) == 0 && lineTwo.compareToIgnoreCase(searchTwo) == 0){
        System.out.println(line);
        linesPrinted++;
    }
}

已验证charAt(0)执行后字符串未被修改，移除charAt(1)相关代码后程序运行正常，确定是该代码引发问题。

解决方案 #

• 优先做长度校验：文件中大概率存在空行或长度小于2的行（比如末尾空行、格式异常的行），哪怕你主观认为所有行都符合长度要求，也必须在调用charAt(1)前判断line.length() >= 2，避免数组越界：

  while(inputFile.hasNext()){
      String line = inputFile.nextLine();
      // 跳过长度不足2的行
      if(line.length() < 2){
          continue;
      }
      String lineOne = String.valueOf(line.charAt(0));
      String lineTwo = String.valueOf(line.charAt(1));
      String searchOne = String.valueOf(search.charAt(0));
      String searchTwo = String.valueOf(search.charAt(1));
  
      if (lineOne.compareToIgnoreCase(searchOne) == 0 && lineTwo.compareToIgnoreCase(searchTwo) == 0){
          System.out.println(line);
          linesPrinted++;
      }
  }
  

• 简化字符比较逻辑：无需将字符转为字符串再比较，直接用Character.toLowerCase()统一大小写后对比，代码更简洁高效：

  while(inputFile.hasNext()){
      String line = inputFile.nextLine();
      if(line.length() < 2){
          continue;
      }
      char lineFirst = Character.toLowerCase(line.charAt(0));
      char lineSecond = Character.toLowerCase(line.charAt(1));
      char searchFirst = Character.toLowerCase(search.charAt(0));
      char searchSecond = Character.toLowerCase(search.charAt(1));
  
      if (lineFirst == searchFirst && lineSecond == searchSecond){
          System.out.println(line);
          linesPrinted++;
      }
  }
  

• 检查search字符串的合法性：还要确认search字符串的长度至少为2，否则search.charAt(1)同样会抛出越界异常，建议在循环外先做一次校验：

  if(search == null || search.length() < 2){
      // 处理search字符串不合法的情况，比如抛出异常或直接返回
      throw new IllegalArgumentException("search字符串长度必须至少为2");
  }
  

内容的提问来源于stack exchange，提问作者Max4