java - 为什么我在执行代码时会收到此 StringIndexOutOfBoundsException？

Question

import java.io.* ;
class Specimen
{
    public static void main(String[] args) throws IOException
    {
        BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Please input the sentence :");
        String s= String.valueOf(bf.readLine());
        System.out.println(s);
        int index ;
        String modif="",part ;
        int c =0 ;
        char ch ;
        String part2;
        while(s.length()>0)
        {
            index = s.indexOf(' ');
            part = s.substring(c,index);
            part = part.trim();
            ch  = part.charAt(0);
            String s1 = String.valueOf(ch);
            modif = modif+ s1.toUpperCase()+".";
            c = index ;
        }
        System.out.println(modif);
    }
}

这是以下问题的代码:

Write a program to accept a sentence and print only the first letter of each word of the sentence in capital letters separated by a full stop. Example:

INPUT SENTENCE : "This is a Cat"
OUTPUT : T.I.A.C.

但是当我执行代码时我得到了

StringIndexOutOfBoundsException: String index out of range: 0

如何解决这个问题？

Answer 1

有几个问题:

    while(s.length()>0) // this is an infinite loop, since s never changes
    {
        index = s.indexOf(' '); // this will always return the index of the first empty 
                                // space or -1 if there are no spaces at all
                                // use index = s.indexOf(' ',c);
        part = s.substring(c,index); // will fail if index is -1
        part = part.trim();
        ch  = part.charAt(0); // will throw an exception if part is an empty String
        String s1 = String.valueOf(ch);
        modif = modif+ s1.toUpperCase()+".";
        c = index ; // this should be c = index + 1
    }