Validate double number

Question

hi all... I need to write a method that validates a user input for double -
so far I've included that it doesn't contain alphabets or other characters such as *.{}, etc
how do I ensure that my sytem doesn't crash if somebody enters an IP Address -
any help would be truely appreciated.
thx

Answer 1

Sorry, didn't read the question properly (that always used to get me into trouble at school). Just realised that you're trying to read a double, so you need to check for the existence of a maximum of one decimal point. Try this:
        // Assume it's valid to start
        boolean isValid = true;
        // Initialise counters
        int count = 0;
        int index = 0;
        // Loop round all characters in the input or until invald character detected
        while (index < userInput.length() && isValid) {
            // Get the next character from the user input
            char c = userInput.charAt(index);
            // Check if it's a decimal point
            if (c == 46) {
                count ++;
                // Invalid if there's been more than one
                if (count > 1) {
                    isValid = false;
            // Check if it's less than the ASCII for '0' or greater than the ASCII for '9'
            } else if (c < 48 || c > 57) {
                isValid = false;
            // Increment the character counter
            index ++;
        // Output the result
        System.out.println("Input valid: " + isValid);
    }By the way, this doesn't allow for negatives, exponentials and the like. I suspect you'll have to go down the parsing route for that.