Regex : MetaCharacter

public class Metacharacters {

    public static void main(String args[]){
        System.out.println("metacharacters d....");//  \\d means digit
        System.out.println(Pattern.matches("\\d", "abc"));//false (non-digit)        System.out.println(Pattern.matches("\\d", "1"));//true (digit and comes once)        System.out.println(Pattern.matches("\\d", "4443"));//false (digit but comes more than once)        System.out.println(Pattern.matches("\\d", "323abc"));//false (digit and char)
        System.out.println("metacharacters D....");//    \\D means non-digit
        System.out.println(Pattern.matches("\\D", "abc"));//false (non-digit but comes more than once)        System.out.println(Pattern.matches("\\D", "1"));//false (digit)        System.out.println(Pattern.matches("\\D", "4443"));//false (digit)        System.out.println(Pattern.matches("\\D", "323abc"));//false (digit and char)        System.out.println(Pattern.matches("\\D", "m"));//true (non-digit and comes once)
        System.out.println("metacharacters D with quantifier....");        System.out.println(Pattern.matches("\\D*", "mak"));//true (non-digit and may come 0 or more times)
    }
}