Pattern

import java.util.regex.Pattern;
import java.util.regex.Matcher;


public class temporaria {
    
    public temporaria() {
    	
    }
    public static void main(String[] args) {
      
                          
         Pattern p = Pattern.compile("([0-9]+)");
         Matcher m = p.matcher("0400e");         
       
         if(m.matches()) {       
        	
         	 System.out.println(m.group(1));
 
         	 
         }         
     } 
}