Question

i have the following problem: i want to read in a String from the user, so far it works pretty well but everytime i press just “return” i get alway the following error:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 0
    at java.lang.String.charAt(String.java:658)
    at Shell.execute(Shell.java:20)
    at Shell.main(Shell.java:55)

This would be the code:

private static void execute(BufferedReader stdin) throws IOException {
    boolean quit = false;
    Field test = new Field();
    while (!quit) {
        System.out.print("ch> ");
        String input = stdin.readLine();
        if (input == null) {
                break;
        }
        String[] tokens = input.trim().split("\\s+");
        tokens[0].toLowerCase();
        char tmp = tokens[0].charAt(0);
        switch (tmp) {
        case 'n':
                test.setPoints(null);
                break;
        case 'a':
                test.add(new Point(Integer.parseInt(tokens[1]), Integer
                        .parseInt(tokens[2])));
                break;
        case 'r':
                test.remove(new Point(Integer.parseInt(tokens[1]), Integer
                        .parseInt(tokens[2])));
                break;
        case 'p':
                System.out.println(test);
                break;
        case 'c':
                System.out.println(test.convexHull());
                break;
        case 'h':
                System.out.println("");
                break;
        case 'q':
                quit = true;
                break;
        default:
                break;
        }
    }
}

Thanks for your help.

Answer 1

If you get an index out of bounds exception when accessing the 0th element, you string is probably empty. You need to add a check for this, checking for null is not enough.

By the way, when you write like this:

tokens[0].toLowerCase();

I highly suspect your tokens[0] remains unchanged. Since strings in java are immutable, toLowerCase will have to return a new string which only contains lower case character.