Update MDB.java

        return null; // Return null if molecule not found

    }

    /**

     * Find the most similar Molecule from the database

     */

    public Molecule similarMolecule(Molecule molecule) {

        // If an exact match is not found then find the most similar

        int maxResult=0;

        Molecule similar=null;

        for (Map.Entry<Integer, ArrayList<Molecule>> entry : db.entrySet()) {

            // Access the key and value of each entry

            Integer numberAtoms = entry.getKey();

            //only check for similarity if they have similar number of atoms within tolerance of 100

            if( (molecule.getNumAtoms()-100)<numberAtoms && numberAtoms<(molecule.getNumAtoms()+100) )

            {

                for (Molecule dbMolecule : db.get(numberAtoms)) {

                    int res = dbMolecule.mostSimilar(molecule);

                    if (res > maxResult) {

                        similar = dbMolecule; // save the similar molecule

                        maxResult = res;

                    }

                }

            }

        }

        return similar;

    }

    /**

     * Find subgraph

     */

    public ArrayList<Molecule> findSubgraph(Molecule molecule) {

        ArrayList<Molecule> returnList = new ArrayList<Molecule>();

        int startingNumber = molecule.getNumAtoms();

        for(int ii : db.keySet()) {

            if (ii >= startingNumber) {

                for(Molecule m: db.get(ii)) {

                    if(m.isSubGraphPresent(molecule) != null) {

                        returnList.add(m);

                        outputTextArea.append(m.moleculeName + "\n\n");

                    }

                }

            }

        }

        return returnList;

    }

    /**

     * Save database to file system

     */