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Write two recursive methods that validate if the given string follows allowed patterns: isIdentifier method checks...

Write two recursive methods that validate if the given string follows allowed patterns:

  1. isIdentifier method checks if the given string is a valid java identifier:
    • must start with a letter,
    • the subsequent characters must be letters or digits
    • the length of a valid identifier must be at least one
  2. isDashDotCode method checks if the given string is a valid word in the following pattern:
    • the characters must be dots or dashes
    • the minimum length of a valid word is one
    • only the following patterns are allowed:
word -> dash OR dot followed by word OR word followed by dash
public class ValidatePatterns
{
    /**
     * Write a recursive method that checks if the given string is a valid java identifier:
     *      must start with a letter,
     *      the subsequent characters must be letters or digits
     *      the length of a valid identifier must be at least one
     */
    private static boolean isIdentifier(String str)
    {
        //TODO Project #2a
        // utilize String methods like: length, substring and charAt
        // utilize Character.isLetter and Character.isLetterOrDigit



        return false; //THIS IS A STUB
    }


    /**
     * Write a recursive method that validates if the given string is a valid word in the following pattern:
     *    the characters must be dots or dashes
     *    only the following patterns are allowed:
     *    word -> dash
     *            OR dot followed by word
     *            OR word followed by dash
     */
    private static boolean isDashDotCode(String str)
    {
        //TODO Project #2b
        // utilize String methods like substring and charAt

        return false; // THIS IS A STUB
    }

    public static void main(String[] args)
    {
        String toCheck = "AB5";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "A?B5";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "5AB5";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "ABcdefg";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "12345A";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "A12345";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));

        System.out.println();
        toCheck = "---";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = ".--";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "..-";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "--.";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "-.-";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));

        toCheck = "-..";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = ".-.";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "...";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "+..";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = ".-.-";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "..--";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "-";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = ".";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "...----";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
    }
}

See the sample run:

Is "AB5" a valid identifier ? --> YES

Is "A?B5" a valid identifier ? --> NO

Is "5AB5" a valid identifier ? --> NO

Is "ABcdefg" a valid identifier ? --> YES

Is "12345A" a valid identifier ? --> NO

Is "A12345" a valid identifier ? --> YES

Is "" a valid identifier ? --> NO

Is "---" a valid DashDot code ? --> YES

Is ".--" a valid DashDot code ? --> YES

Is "..-" a valid DashDot code ? --> YES

Is "--." a valid DashDot code ? --> NO

Is "-.-" a valid DashDot code ? --> NO

Is "-.." a valid DashDot code ? --> NO

Is ".-." a valid DashDot code ? --> NO

Is "..." a valid DashDot code ? --> NO

Is "+.." a valid DashDot code ? --> NO

Is ".-.-" a valid DashDot code ? --> NO

Is "..--" a valid DashDot code ? --> YES

Is "-" a valid DashDot code ? --> YES

Is "." a valid DashDot code ? --> NO

Is "...----" a valid DashDot code ? --> YES

Is "" a valid DashDot code ? --> NO

Process finished with exit code 0

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Homework Answers

Answer #1 
public class ValidatePatterns
{
    /**
     * Write a recursive method that checks if the given string is a valid java identifier:
     *      must start with a letter,
     *      the subsequent characters must be letters or digits
     *      the length of a valid identifier must be at least one
     */
    private static boolean isIdentifier(String str)
    {
        //TODO Project #2a
        // utilize String methods like: length, substring and charAt
        // utilize Character.isLetter and Character.isLetterOrDigit
        int length = str.length();
        if (length == 0)
            return false;

        char c = str.charAt(length - 1);

        if (length == 1) {
            if (Character.isLetter(c))
                return true;
            else
                return false;
        } else {
            if (Character.isLetterOrDigit(c))
                return isIdentifier(str.substring(0, length - 1));
            else
                return false;
        }

    }

    private  static boolean isDashDotCode(String str) {
        return isDashDotCodeBase(str, false, '\0');
    }
    /**
     * Write a recursive method that validates if the given string is a valid word in the following pattern:
     *    the characters must be dots or dashes
     *    only the following patterns are allowed:
     *    word -> dash
     *            OR dot followed by word
     *            OR word followed by dash
     */
    private static boolean isDashDotCodeBase(String str, boolean switched, char previous)
    {
        //TODO Project #2b
        // utilize String methods like substring and charAt
        int length = str.length();
        // store state, i.e. whether pattern has been switched one time

        if (length == 0) {
            if (previous == '\0')
                return false;
            else
                return true;
        }

        else {
            char a = str.charAt(0);
            if (a != '.' && a != '-')
                return false;
            if (previous != '\0' && a != previous) {
                if (switched)
                    return false;
                return isDashDotCodeBase(str.substring(1), true, a);
            } else {
                return isDashDotCodeBase(str.substring(1), switched, a);
            }
        }
    }

    public static void main(String[] args)
    {
        String toCheck = "AB5";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "A?B5";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "5AB5";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "ABcdefg";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "12345A";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "A12345";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));
        toCheck = "";
        System.out.println("Is \"" + toCheck + "\" a valid identifier ? --> "
                + (isIdentifier(toCheck) ? "YES" : "NO"));

        System.out.println();
        toCheck = "---";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = ".--";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "..-";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "--.";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "-.-";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));

        toCheck = "-..";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = ".-.";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "...";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "+..";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = ".-.-";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "..--";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "-";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = ".";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "...----";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
        toCheck = "";
        System.out.println("Is \"" + toCheck + "\" a valid DashDot code ? --> "
                + (isDashDotCode(toCheck) ? "YES" : "NO"));
    }
}
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