I don't like 2 points:

1 - your static connection variables:

// Connection variables
static Connection conn = null;

if you want to access the connection from everywhere, create a singleton class ConnectionManager.

2 - int balance[] = new int[2]; you should create a new class with 2 fields checking/saving

I don't like 2 points:

1. Your static connection variables:

    // Connection variables
    static Connection conn = null;
   

If you want to access the connection from everywhere, create a singleton class ConnectionManager.

2. int balance[] = new int[2];

You should create a new class with 2 fields checking/saving.