Unicode Character

            The char type is a primitive that holds what?

Single Unicode character which is stored in two bytes. 

The list of unicodes  are given linked below.

http://en.wikipedia.org/wiki/List_of_Unicode_characters

The unicode for your native language is linked below:

http://en.wikipedia.org/wiki/Tamil_script

StringBuilder class

String classes create Strings that are immutable in other words when you use the String class to work with strings, the string has a fixed length and you can't edit the characters that make up the string. If you assigne a new value to a string variable, the original String object is deleted an it's replaced with a new String object that contains the new value. StringBuilder was introduced with Java 1.5 with more flexibililty and is mutable, meaning you can add, delete or replace the characters in a StringBuilder object.

http://docs.oracle.com/javase/tutorial/java/data/buffers.html

try-with-resources

Java 1.7 introduced try-with-resources statement: It uses objects that implement the java.lang.AutoCloseable interface and hence you don’t have to use finally block to close the resources.

try (RandomAccessFile in = new RandomAccessFile("file.ran", "r"))

        {           

            String s = in.readLine();

            return s;

        }

        catch (FileNotFoundException e)

        {

            System.out.println("File not found");

            System.out.println(e.toString());

            return null;           

        }

        catch (IOException e)

        {

            System.out.println("I/o error occurred");

            System.out.println(e.toString());

            return null;

        }

SSN Validator using matches()

SSNValidatorApp : You can use this to validate a textfield. Here it is SSN. Or see below for an easier method to validate.

public class SSNValidatorApp{

    public static void main(String[] args)    {

        boolean isValid =  false;

        while(!isValid)        {

        Scanner sc = new Scanner(System.in);    

        isValid = Validator.getSSN(sc, "Enter a Social Security Number: ");

        if(isValid)

            System.out.println("It is a valid SSN. Thank you");

        else

            System.out.println("It is an invalid SSN. Please try again");

        }    }  

public static boolean getSSN(Scanner sc, String prompt)    {

        System.out.print(prompt);

        String ssn = sc.nextLine();

        boolean isNumeric = false;       

            if(ssn.length() == 11)            {               

                if(getNumeric(ssn.substring(0, 3)))                {

                    if(ssn.charAt(3) == '-')                    {

                        if(getNumeric(ssn.substring(4, 5)))                        {

                            if(ssn.charAt(6) == '-')                            {

                                if(getNumeric(ssn.substring(7, 11)))                                {

                                    isNumeric = true;

                                }          }           }            }                }            }   

        return isNumeric;        }

   

    public static boolean getNumeric(String subString)    {

        boolean isNumeric = false;

        int i = 0;        

        while(i <= (subString.length()-1))        {

            char subStringLetter = subString.charAt(i);          

            switch(subStringLetter)           {

                case('0'):                  

                    isNumeric = true;

                    break;

                ………….. //put all cases  from 0 to 9 here

                case('9'):

                    isNumeric = true;

                    break;

                default:

                    isNumeric = false;                    

            }

            if(isNumeric)

                i++;

            else

                break;

        }

        return isNumeric;      

      }}}

Here is the easier way of doing it. Use matches() in Regular Expression provided by Java API. You can include the java documents in eclipse by clicking :    windows> show view> java docs if you want to see the description of the method you are using

public class SSNValidator {
        public static void main(String[] args) {
                SSNValidator ssnValidator = new SSNValidator();

                String[] ssnList = { null, "", "909-90-9900", "3423-343-23423",
"312fsdfas-sdfsaf-sadfas", "ada-dd-dasd",
                                "123-32-4532", "123*32*4532", "\t" };

                for (String ssn : ssnList) {
                        System.out.println("SSN Value [" + ssn + "] is " +
(ssnValidator.isValid(ssn) ? "valid" : "invalid") + ".");
                }
        }

        public boolean isValid(String ssn) {

                return ssn != null && ssn.matches("\\d{3}-\\d{2}-\\d{4}");

        }
}