Input/output string line from text file

FileManager.java

import java.io.*;
import java.util.ArrayList;

public class FileManager {

    private static volatile FileManager instance;
    private static final Object lock = new Object();
    private final ArrayList<String> msg;
    private final String FILE_NAME = "Data.txt";

    private FileManager() {
        msg = new ArrayList<String>();
    }

    public static FileManager Get() {
        if (instance == null) {
            synchronized (lock) {
                instance = new FileManager();
            }
        }
        return instance;
    }

    void addToWrite(String s) {
        msg.add(s);
    }

    public void addToWrite(ArrayList<String> sList) {
        for (String s : sList)
            addToWrite(s);
    }

    public void save(String filePath) {
        File file;
        try {
            file = new File(filePath);
            file.createNewFile();
            PrintWriter output = new PrintWriter(new FileWriter(file));
            for (String s : this.msg) {
                output.println(s);
            }
            output.close();
        } catch (IOException e) {
            System.err.print(e);
        }
    }


    public void save() {
        save(FILE_NAME);
    }

    public ArrayList<String> load(String filePath) {
        ArrayList<String> stringList = new ArrayList<String>();
        FileInputStream stream;
        try {
            stream = new FileInputStream(FILE_NAME);
            BufferedReader br = new BufferedReader(new InputStreamReader(new DataInputStream(stream)));
            String strLine;
            while ((strLine = br.readLine()) != null) {
                stringList.add(strLine);
            }
        } catch (IOException e) {
            return new ArrayList<String>();
        }
        return stringList;
    }

    public ArrayList<String> load() {
        return load(FILE_NAME);
    }
}