java - Java简介: How to use an if statment when a string doesn't exist

Question

当有人只输入他们的两个名字时，我试图让代码输出，但我无法弄清楚。我尝试过使用 if (nameFML==null) 和 (nameFML[2].isEmpty()) 但每当我仍然收到“thread main java.lang.arrayindexoutofboundsexception: 2”错误时我输入一个名字，比如 John Doe。除此之外，程序会执行它应该执行的操作。

    import java.util.Scanner;
    public class Assignment3
    {
      public static void main(String[] args)
      {

       //Declaring variables
        String inputName;
        Scanner in = new Scanner(System.in);

       //Asking user for keyboard input.
        System.out.println("What are your first, middle, and last names? ");
        inputName = in.nextLine();

       //Users First Input restated
        System.out.println(inputName);

       //Splitting the string "inputName" up by making spaces(" ") delimiters.
       if (inputName.contains(" "))
        {
          String[] nameFML = inputName.split(" ");

       // Creates new strings from the new "nameFML" variable, which was created from "inputName" being split.
          String firstInitial = nameFML[0].substring(0,1).toUpperCase();
          String middleInitial = nameFML[1].substring(0,1).toUpperCase();
          String lastInitial = nameFML[2].substring(0,1).toUpperCase();

       //The if method determines whether or not the user inputed in three tokens, two, or an incorrect amount.
          if (nameFML.length== 2)
          {
            System.out.println("Your initials are: " + firstInitial + middleInitial);

        //Separated the print the Variation One print command because it's the only way I could get ".toUpperCase" to work properly.
            System.out.print("Variation One: " + (nameFML[1].toUpperCase()));
            System.out.println(", " + nameFML[0]);

            System.out.println("Variation Two: " + nameFML[1] + ", " + nameFML[0]);


          }
          else
          {
            System.out.println("Your initials are: " + firstInitial + middleInitial + lastInitial);

        //Separated the print the Variation One print command because it's the only way I could get ".toUpperCase" to work properly.
            System.out.print("Variation One: " + (nameFML[2].toUpperCase()));
            System.out.println( ", " + nameFML[0] + " " + lastInitial + ".");

            System.out.println("Variation Two: " + nameFML[2] + ", " + nameFML[0] + " " + nameFML[1]);
          }
        }
        else
        {
      System.out.println("Wrong. Please enter your name properly.");
    }
  }
}

Answer 1

问题是，如果字符串只有两部分，则数组的第三个元素(索引 2)不为空 - 它只是不存在。因此，代码在

处失败

String lastInitial = nameFML[2].substring(0,1).toUpperCase();

如果你移动这些行

String firstInitial = nameFML[0].substring(0,1).toUpperCase();
String middleInitial = nameFML[1].substring(0,1).toUpperCase();
String lastInitial = nameFML[2].substring(0,1).toUpperCase();

进入适当的 if 语句，一切都应该正常工作。 nameFML.length 是要检查的正确内容。

供将来引用，thread main java.lang.arrayindexoutofboundsException: 2 中的异常:2 表示您尝试访问少于 3 个元素的数组的索引 2 (当您执行 nameFML[2] 时发生的情况)。