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我正在尝试编写一个程序来获取用户输入的第一个字母来生成用户名。我正在尝试编写它，以便如果用户将输入留空，则用于生成用户名的字母默认为字母“z”。

这是我的完整代码：

    import java.util.Scanner;
    /**
      UsernameGenerator.java
      Generates a username based on the users inputs.
      @author: Evan Fravert
      */
public class UsernameGenerator {
/**
  * Generates a username based on the users inputs.
  *@param args command line argument
  */
  public static void main(String[] args)
{ // abcde
  String first;
  String middle;
  String last;
  String password1;
  String password2;
  int randomNum;
  randomNum = (int) (Math.random() * 1000) + 100;
  Scanner userInput = new Scanner(System.in);
  System.out.println("Please enter your first name:");
  first = userInput.nextLine();
  String firstLower = first.toLowerCase();
  System.out.println("Please enter your middle name:");
  middle = userInput.nextLine();
  String middleLower = middle.toLowerCase();
  System.out.println("Please enter your last name:");
  last = userInput.nextLine();
  int lastEnd = last.length()-1;
  String lastLower = last.toLowerCase();
  System.out.println("Please enter your password:");
  password1 = userInput.nextLine();
  System.out.println("Please enter your password again:");
  password2 = userInput.nextLine();

  char firstLetter = firstLower.charAt(0);
  char middleLetter = middleLower.charAt(0);
  char lastLetter = lastLower.charAt(0);
  char lastLast = lastLower.charAt(lastEnd);

  if first.length() == 0) {
      firstLetter = 'z';
  }
  else {
  firstLetter = firstLower.charAt(0);
  }

  System.out.println("Your username is " + firstLetter + ""
  + middleLetter + "" + lastLetter + "" + "" + lastLast + "" + randomNum); 
  System.out.println("Your password is " + password1);
  System.out.println("Welcome " + first + " " + middle + " " + last + "!");
}
}
4

3 回答 3

2

这是行不通的：

char firstLetter = firstLower.charAt(0);
...

if (first.length() == 0) {
    firstLetter = 'z';
}

如果长度为0，那么charAt(0)会在标题中抛出异常。你可以这样做：

char firstLetter = first.length() == 0 ? 'z' : firstLower.charAt(0);
于 2012-09-12T03:36:23.470 回答
1

这里可能会抛出异常：

char firstLetter = firstLower.charAt(0);

您在检查输入是否为空charAt(0) 之前调用。尝试这样的事情：

char firstLetter = first.isEmpty() ? 'z' : firstLower.charAt(0);

请注意，这first.isEmpty()是一个等价的表达式first.length() == 0。

于 2012-09-12T03:36:02.340 回答
0

你从这条线得到例外

char firstLetter = firstLower.charAt(0);

低于一个就足以得到第一个字母。所以只保留这个

char firstLetter;
if (first.length() == 0) {
      firstLetter = 'z';
  }
  else {
  firstLetter = firstLower.charAt(0);
  }

以同样的方式，您必须检查其他输入字符串值

于 2012-09-12T06:45:29.117 回答