A simple example of writing a java object to a file.

serialize

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

class wallet implements java.io.Serializable {

    private double balence;

    public double check() {
        return balence;
    }

    public double add(double num) {
        return balence += num;
    }

    public static void main(String[] args) {
        if (args.length > 0) {

            String filename = args[0];
            wallet mywallet = new wallet();

            FileOutputStream fos = null;
            ObjectOutputStream out = null;

            try {
                fos = new FileOutputStream(filename);
                out = new ObjectOutputStream(fos);
                out.writeObject(mywallet);

                out.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        } else {
            System.out.println("Please enter wallet name.");
        }
    }
}