Update MDB.java

import edu.bu.ec504.project.Molecule;

import javax.swing.*;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

import java.io.*;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.Map;

import java.util.List;

/**

 * A class represents the molecule database that works with the GUI.

        return returnList;

    }

    /**

     * Download Molecules from Pubchem in range [start, end]

     */

    public void downloadPubChem(String start, String end) {

        String scriptPath = "testcases/downloadPubChem.py";

        List<String> filenames = new ArrayList<>();

        try {

            // build Python script call

            ProcessBuilder builder = new ProcessBuilder("python", scriptPath, start, end);

            Process process = builder.start();

            // get Python filename output

            InputStream stdout = process.getInputStream();

            BufferedReader reader = new BufferedReader(new InputStreamReader(stdout));

            String file;

            while ((file = reader.readLine()) != null) {

                outputTextArea.append("file created: " + file + "\n\n");

                filenames.add(file);

            }

            int exitCode = process.waitFor();

            outputTextArea.append("Exited with code: " + exitCode + "\n\n");

            // add created files to the database

            for (String filename : filenames) {

                this.addMolecule(new Molecule(filename));

            }

        } catch (Exception e) {

            outputTextArea.append("Error downloading from PubChem" + "\n\n");

            e.printStackTrace();

        }

    }

    /**

     * Save database to file system