java string match

java-string-match.java

import java.util.*;
import java.util.regex.*;
class NumRegex
{
	public static void main(String args[])
	{
		// Create a regular expression that matches
		// any number You know all this! This is why you came here ;)
		// What matches and what doesn't?
		// 1 matches
		// 24133242 matches
		// 2342332d doesn't match (it contains d at last!)
		// 23432 233 doesn't match (it contains a space)
		// asdfsafd doesn't match (it is not a number)
	    
		// What's the +?
		// More 1 or more than 1 digit
		// \\d is for a signle digit
		String numRegex="^[\\d]+$";
	    
		// This is another way, isn't it lengthy?
		// Yet, remember it!
		// String numRegex="^[0-9]+$";
	    
		// Hmm, one more. What if i want only a 2 digit number
		// Replace 2 with whatever you no.of digits you want in
		// the number.
		// String numRegex="^[\\d]{2}$";
	    
		// Create a Scanner object
		Scanner s=new Scanner(System.in);
	    
		// Give the regex for compilation.
		// Don't worry, it gives a Pattern object in return! ;)
		Pattern p=Pattern.compile(numRegex);
	    
		// Ask the user to enter a number, else he
		// scratches his head of what to do!
		System.out.println("Enter the number");
	    
		// Read a line, use nextLine(). If you forgot
		// Line and simply use next(), you don't get spaces!
		String st=s.nextLine();
	    
		// Create a Matcher, not a match box! ;)
		// See if what user has given is a number!
		Matcher m=p.matcher(st);

    		// Now, print whether the user understood what we said!
		System.out.println(m.matches()?"You entered a number! Great! you understood the question :)":"I asked for number!!!!");
	}
}