getting StringIndexOutOfBound Exception

Question

I am writing a program to accept user name and password using following conditions- username must be min 8 characters. Password must have min 10 characters, 1 lowerCase, 1 upperCase, 1 digit should present in the password. I wrote a method setPassword() following all the conditions. When I try to execute I am getting StringIndexOutOfBound exception. I am unable to understand why I am getting that error:

public void setPassword(String password)
{
    char ch;
    if (password.length() <= 10) {
        for (int i = 0; i <= password.length() - 1; i++) {
            ch = password.charAt(i);
            if (Character.isDigit(ch)) {
                for (int j = 0; j <= password.length() - 1; j++) {
                    char ch1 = password.charAt(j);
                    if (Character.isUpperCase(ch1)) {
                        for(int k = 0; k <= password.length(); k++) {
                            char ch2 = password.charAt(k);
                            if (Character.isLowerCase(ch2)) {
                                this.password = password;
                            }
                        }
                    }
                }
            }
        }
    }
}

Answer 1

Ignoring the inefficiencies of this implementation, the following line:

for(int k = 0; k <= password.length(); k++) {

Should either be:

for(int k = 0; k < password.length(); k++) {
//                ^ removed the = from here

Or:

for(int k = 0; k <= password.length() - 1; k++) {
//                                    ^ subtract 1 here

For the following string:

String s = "this-is-a-test";

s.length() is going to return 14. The valid indices of characters in that string are 0 through 13. The idiomatic way of iterating over an array with a for loop is:

for (int i = 0; i < length_of_array; i++)

You've opted to instead use i <= length_of_array - 1 which is effectively the same thing (albeit more verbose), except for your last for loop where you neglect to subtract 1 from the length.

Here is a simplistic method for checking password validity based on the criteria you provided:

public static boolean isPasswordValid(String password)
{
    if (password.length() < 10) {
        return false;
    }

    int lc = 0, uc = 0, digit = 0;

    for (int i = 0; i < password.length(); i++) {
        char c = password.charAt(i);

        if (Character.isLowerCase(c)) {
            lc++;
        } else if (Character.isUpperCase(c)) {
            uc++;
        } else if (Character.isDigit(c)) {
            digit++;
        }
    }

    return lc > 0 && uc > 0 && digit > 0;
}

This will return true if all of the conditions pass, and false otherwise.