Java中使用charAt的“字符串索引超出范围”错误消​​息

Question

Recently, while coding I came upon the following error:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: 
                     String index out of range: 0
at java.lang.String.charAt(String.java:686)
at TestAssign2.main(TestAssign2.java:119)

The error appears when I add the line - firstLetter=userName.charAt(0); to the code and program displays the error message after the user enters all the values asked. Before this line was entered, it all worked fine.

while(uProgStart.equals(PROGSTART))
        {


            System.out.println("What is your name?");
            userName=sc.nextLine();
            junk = sc.nextLine();



            System.out.println("What is the year of your birth?");
            birthYear = sc.nextInt();
            junk = sc.nextLine();

            System.out.println("What is the date of your birth? (dd.mm)");
            birthDDMM = sc.nextDouble();
            junk = sc.nextLine();



            day=(int)birthDDMM;

            month=(int)Math.round(100*birthDDMM)%100;

                //Begins calculation of Dss Score
                if(birthYear%CYCLE_LENGTH!=SNAKE_YEAR)
                    {
                        DssScore=DssScore+1;
                    }

                if(month<SPRING_BEGINNING||month>SPRING_END)

                    {
                        DssScore=DssScore+2;
                    }

     firstLetter=userName.charAt(0);            
            if(firstLetter==(LOWER_S)||firstLetter==(UPPER_S))
                {
                    DssScore=DssScore+4;
                }

The idea of the line was to see if the name entered by the user begins with either the letter 's' or 'S'.

All the variables have been declared, I just haven't included them for the sake of keeping this post a little succinct.

Answer 1

I think you are pressing enter key by mistake without giving a chance to enter any input and it forces username variable be empty. I reproduced this error like mentioned above.Sometime when you deal with scanner , it happens like that.

So in your code, check whether the username is null or not before doing any operation.

Answer 2

在charAt调用之前，对sc.nextLine()的调用sc.nextLine()用于分配userName sc.nextLine()可能返回一个空字符串（例如，如果您扫描空白行）。

Answer 3

You may want to use if to make sure that the next line really exists.

Something like this:

if(sc.hasNextLine()) {
   userName = sc.nextLine()
} else {
  System.out.println("OMG... Where is my line?")
}

This most likely not a good fix for your problem, but based on the limited information we have it's difficult to suggest anything better.

The real problem is most likely elsewhere in your logic.