Chemical Formulae (contd.)

Question

import java.util.regex.*;
public class ChemicalFormulae {
/* names should be loaded dynamically from that file */
private String[] names = {"H", "C", "Ca", "O"};
private Matcher matcher = null;
private Pattern pattern = null;
static java.io.PrintStream p = System.out;
public static void main(String[] args) {
ChemicalFormulae inoh = new ChemicalFormulae();
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 ChemicalFormulae() {
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;
private static void order() {
p.println("Would you like fries with that?");
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)");
}This one here is my first attempt...However I need to run the program using an IDE not DOS....what this does is, it
needs arguments for the program to work corretly.... To make the Program work, TYPE "java ChemicalFormulae CaCO3" ((Or "H2O" or whatever))
Or in an IDE, go to RUN With ARFGUMENTS and type in there CaCO3 for example.
See what happens...
Now I need to be able to allow the user to enter in those arguments in run-time mode. ((The Program needs Arguments to Work Correctly))
You said earlier that 'system.in' works for this....I will experiment with this tomorrow morning. <<I'm tired>>
In CaCO3 for example, where each element in a compound is identified by a symbol corresponding an upper case character that may be followed by a lower case one. If there is a numerical character following a symbol, that indicates the number of atoms of that element. if there is no numerical value present, then there is 1 atom present.
EG... if the user enters... "CaCO3", The output should be:
Ca for Calcium (1 atom)
C for Carbon (1 atom)
O for Oxygen (3 atoms)
""I need to write a java application that asks the user for a chemical formulae...the application should then analyse the formuale and identify the symbols present together and the number of atoms of the corresponding element. the elements should then be identified from the file of element data and a table displayed showing the elemnts present with the corresponding number of atoms.""
The file looks something like this:
Ag Silver
Au Gold
Al Aluminium
C Carbon
Ca Calcium
etc....
I made a GUI interface in one of my later versions, so the user can enter in his chemical formulae (arguments) and the program would work...but I couldn't make the arguments work in run-time. ((System.In I was told works....so I'll look into it....thanks to whomever suggested it))
Also....about reading the file, your advice all sounds too complicated for a n00b like me....are there any tutorials on this that can help me.
Any Guidance would be appreciated....
Please try and run the program so you get a feel of what I mean.
Thanks Again...
(( To run the Program from DOS just type "java ChemicalFormulae CaCO3"
((Or H2O, or whatver))
:)

Answer 1

for beginners, you should use FileReader and a BufferedReader like so:
first import java.io.*;
make a method that loads the file into some global object.
BufferedReader in = new BufferedReader(new FileReader("Filename"));
in order to read the file, you can use in.readLine() which will give you one line at a time. Just remember when you are at the end of the file, in.readLine() will return null, so you have to watch out for that.
You could store the values in 2 equal size String arrays, which I'm sure you know how to do, but I'm sure everyone will agree that you should use a hashmap since all of the entries are unique.
The API for a HashMap is here:
http://java.sun.com/j2se/1.4.2/docs/api/java/util/HashMap.html
The tutorial for all colections is:
http://java.sun.com/docs/books/tutorial/collections/index.html
I'm guessing you are a college student working on an assignment, eventually you will learn Collections eventually, might as well take a stab at it. You will find that once you learn it, you will find it is far easier to manage for this purpose than 2 arrays.