Java: String index out of range: -1

Question

New code:

I have no idea what's going on here, I'm getting this error:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -1
    at java.lang.String.substring(String.java:1949)
    at client0_0_2.loginToClient(client0_0_2.java:98)
    at client0_0_2.general(client0_0_2.java:196)
    at client0_0_2.<init>(client0_0_2.java:208)
    at client0_0_2.main(client0_0_2.java:215)

and this is the contents of the method that's causing the error:

public String loginToClient() throws FileNotFoundException, IOException {
    //decryptUsers();
    int tries;
    tries = 5;
    while (tries > 0) {
        System.out.println("LOGIN");
        String usnm = c.readLine("Username: ");
        char [] passwd = c.readPassword("Password: ");
        users = new FileInputStream("users.fra");
        DataInputStream dis = new DataInputStream(users);
        BufferedReader br = new BufferedReader(new InputStreamReader(dis));
        String logindat = br.readLine();
        System.out.println(logindat);
        int startUsnm = logindat.indexOf(usnm);
        String logdat = logindat.substring(startUsnm, logindat.indexOf("."));
        if (startUsnm == -1) {
            System.err.println("Username not recognised, please try another or create user.");
            usnm = "INV";
            return usnm;
        }
        else {
            int tendUsnm = logdat.indexOf(':'); 
            int startPass = endUsnm + 1;
            int tendPass = logdat.indexOf('.');
            String Usnm = logdat.substring("0", tendUsnm);
            String Pass = logdat.substring(startPass, endPass);
            char [] Passwd = Pass.toCharArray();
            if (usnm.equals(Usnm)) {
                if (Arrays.equals(passwd,Passwd)) {
                    System.out.println ("Logged in. Welcome, " + usnm + ".");
                    String data = "LOGIN: " + usnm;
                    printLog(data);
                    //encryptUsers();
                    return usnm;
                }
                else {
                    System.out.println ("Incorrect password, please try again.");
                    String data = "PASWFAIL: " + usnm;
                    printLog(data);
                    tries -= 1;
                }
            }
            else {
                System.out.println ("Username not recognised.");
                printLog("USNAMFAIL");
                usnm = "INV";
                return usnm;
                //encrytUsers();
            }
        }
    }
    //encryptUsers();
    System.exit(2);
    return usnm;
}

It looks kinda like it's trying to access the last character of something and that's upsetting it, but I have no idea why. Any help for a total newbie?

edits:

users.fra contains username:password at the time of execution.

note: line 98 is the

char [] Passwd = Pass.toCharArray();

n.b. not homework, a personal project.

Will add in a method to deal with the event that username is not in users.fra.

I don't think this is line 98 `char [] Passwd = Pass.toCharArray();` — jn1kk, May 30 '12 at 14:29
i believe the compiler may have pinpointed the wrong line, as it sometimes does. — gossfunkel, May 30 '12 at 14:45

score 3 · Answer 1 · answered May 30 '12 at 14:26

3

indexOf() returns -1 when the argument can't be found. I bet that the string you are searching does not have one of the characters you are searching for and it is causing an invalid index when you try to get a substring.

answered May 30 '12 at 14:26

unholysampler

17,141
7
47
64

Thanks! It shouldn't be... it's finding a plaintext username and password in a file containing only "username:password.", so I presume I've screwed up one of the searches... – gossfunkel May 30 '12 at 14:29

score 3 · Answer 2 · answered May 30 '12 at 14:27

3

try to use contains() before indexOf() for yor string to avoid the situations when indexOf() returns -1 and you try to get substring with the -1 position.

answered May 30 '12 at 14:27

Alex Stybaev

4,623
3
30
44

How exactly should I use `contains()`? – gossfunkel May 30 '12 at 14:58
e.g.: `if(myString.contains(someChar) && myString.contains(someOhterChar)) { String subString = myString.substring(myString.indexOf(someChar), myString.indexOf(someOhterChar))` – Alex Stybaev May 30 '12 at 15:34

score 2 · Answer 3 · answered May 30 '12 at 14:28

2

String().indexOf will return -1 if there is no match

String().substring will throw an StringIndexOutOfBoundsException if you give it a negative begin value.

This is all documented at http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/String.html

Thus, I'd look at this line of code:

String logdat = logindat.substring(startUsnm, logindat.indexOf("."));

This will fail if usnm is not in logindat

answered May 30 '12 at 14:28

Dancrumb

26,597
10
74
130

substring() Throws: IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex. – Manoj Mar 22 '21 at 05:07

Denys Séguret · Answer 4 · 2012-05-30T14:59:02.457

A lot of things can be wrong. You'll have to check what is printed.

An exemple :

int startUsnm = logindat.indexOf(usnm);
String logdat = logindat.substring(startUsnm, logindat.indexOf("."));

If you don't have "Username: " in logindat, it produces the exception you see.

EDIT : Note that if you want to allow "username:" (and not only "Username:"), you can do this :

 int startUsnm = logindat.toLowerCase().indexOf("username:");

And test that startUsnm is >= 0.

score 0 · Answer 5 · answered May 30 '12 at 14:43

You should really look at those lines:

        int startUsnm = logindat.indexOf(usnm);
        int tendUsnm = logdat.indexOf(':');
        int endUsnm = startUsnm + tendUsnm;
        int startPass = endUsnm + 1;
        int tendPass = logdat.indexOf('.');
        int endPass = startPass + tendPass;
        String Usnm = logindat.substring(startUsnm, endUsnm);
        String Pass = logindat.substring(startPass, endPass);

Suppose you have file like this:

user:pass.

so:

startUsnm = 0 //first char
tendUsnm = 4 // index of : char
endUsnm = 4 // sum? this is probably not what you intent to do
startPass = 5 // p char
tendPass = 9 // . char
endPass = 14 // sum again? Those integers are indexes - will throw IndexOutOfBounds

And consider also that indexOf will return -1 value if there is no such match in given String.

the summed integers are for if the username required is not the first in the users.fra file; id est, it may contain "username:password.usrn:pass." and I only seek usrn, not username. This should give me the position of the end of the username with respect to the whole string. Which I've just realised is a pointless exercise, as I have a string which is only the index of usrn through to "."... Will now adjust. — gossfunkel, May 30 '12 at 14:49

Java: String index out of range: -1

5 Answers5