IndentifierCheck.java

import java.util.ArrayList;
import java.util.Scanner;

public class IdentifierCheck
{

    public static void main(String[] args)
    {
        // input from user
        Scanner in = new Scanner(System.in);
        String name = " ";
        char sp;

        System.out.println("This program checks the properness of a proposed Java variable name.");

        while (true) {

            ArrayList<String> errors = new ArrayList<String>();

            System.out.println("Enter a variable name. (q to quit):");
            name = in.nextLine();

            if (name.charAt(0) == 'q' && name.length() == 1) break;

            for (int i = 0; i < name.length(); i++)
                {
                    sp = name.charAt(i);

                    if (Character.isWhitespace(sp))
                        {
                            if(!errors.contains("Illegal, no whitespace allowed."))
                                errors.add ("Illegal, no whitespace allowed.");
                        }

                    else if (Character.isDigit(sp) && i == 0)
                        {
                            errors.add ("Illegal, must begin with a letter.");
                        }
                    else if (Character.isLetterOrDigit(sp))
                        {
                            if(Character.isLowerCase(sp) && i == 0)
                                {
                                    errors.add("Warning, it would be better with the first letter in uppercase.");
                                }
                        }
                    else {
                        errors.add("Illegal, must only contain letters and digits.");
                    }
                }
            if(errors.size() == 0) {
                System.out.println("Well done, that's a nice variable name.");
            } else {
                System.out.println("You had errors:");
                System.out.println(errors);
            }
            
        }
    }
}