Help with getting this to work!

Question

Hi,
I am trying to get this Java application to work - but nothing seems to happen! Basically, its a chemical formulae analyser, e.g. in CaC03, C is the symbol for Carbon and there is 1 atom of this element, Ca for Calcium (1 atom), O for Oxygen (3 atoms). The application should ask the user for input (chemical formulae) and then analyse the formula and identify the symbols present together and the number of atoms of the corresponding element.
The elements should then be identified and a table displayed showing the elements present together with the corresponding number of atoms. Appropriate error messages should be displayed for any invalid data.
Now the code I have seems fine to me, but when you run the application, nothing happens! There are no error messages, but just nothing happens! I have two files, InNeedOfHelp.java and InNeedOfHelp.class, and the InNeedOfHelp.java file contains the following code (but nothin happens when run as I have stated!): -
import java.util.regex.*;
public class InNeedOfHelp {
/* names should be loaded dynamically from that file */
private String[] names = {"H", "C", "Ca", "O"};
private Matcher matcher = null;
private Pattern pattern = null;
public static void main(String[] args) {
InNeedOfHelp inoh = new InNeedOfHelp();
for (int i = 0; i < args.length; i++) {
if (inoh.isValid(args[ i])) {
inoh.check(args[ i]);
} else {
System.out.println("Illegal formula: " + args[ i]);
public InNeedOfHelp() {
String regex = "([A-Z][a-z]?+)([0-9]*+)";
pattern = Pattern.compile(regex);
matcher = pattern.matcher("");
/* Element name needs real solution, current implementation is too static ;) */
private String getElementName(String s) {
if ("H".equals(s)) {
return "Hydrogen";
} else if ("O".equals(s)) {
return "Oxygen";
} else {
return s;
private String getElementCount(String s) {
if ("".equals(s)) {
return "1";
} else {
return s;
public boolean isValid(String formula) {
String regex = "((";
for (int i = 0; i < names.length; i++) {
regex += (i == 0 ? "(" : "|(") + names[ i] + ")";
regex += "){1}[0-9]*)+";
return formula.matches(regex);
/* check needs better name and should be redesigned to just collect data */
public void check(String formula) {
int end = 0;
matcher = matcher.reset(formula);
while (matcher.find(end)) {
end = matcher.end();
System.out.println("Element " + getElementName(matcher.group(1))
+ " occured " + getElementCount(matcher.group(2)) + " time(s)");
So, if anyone could help me with this application I would be very grateful! Thanks guys.

Answer 1

If nothing happens, as a first step I suggest putting in some System.out.println statements in the main method to find out what happens with isValid(). It usually makes sense to look for easy problems first. May be your command line arguments are not valid, or your isValid methods thinks they aren't anyway.