check if a string contains a number in java

/**
 * @author lautturi.com
 * Java example:  find the number in a java string 
 */

import java.util.*;
import java.io.IOException;

public class Lautturi {
	
	public static void main(String[] args)  {

		String sample = "utf-8";
	      char[] chars = sample.toCharArray();
	      StringBuilder sb = new StringBuilder();
	      for(char c : chars){
	         if(Character.isDigit(c)){
	            sb.append(c);
	         }
	      }
	      System.out.println(sb);
	}
	
}