Code:

public static void connect() {
        
        if(conn==null) {
            
            try {
                //login data 
                String userName = "sa";
                String password = "";
                
                //driver loading
                Class.forName("org.hsqldb.jdbcDriver");
                
                //url specification
                String url = "jdbc:hsqldb:/home/ivan/MyBookstore/MyBookstore";

                //getting connection
                conn = DriverManager.getConnection(url, userName, password);
                
                //setting Connection state
                connState = true;
                System.out.println("Database connection OPENED");
                if(conn.isClosed()) {System.out.println("CLOSSSSEEEES"); }
              
            } catch (Exception e)
                {        
                System.out.println("Cannot connect to database server --> " + e);
                }
        
        }
        else {
            System.out.println("Allredy Connected");
        }
    }
    
    //DISCONNECT Method
    public static void disconnect() {
            System.out.println("Database Connection CLOSED");
            try {
                stmt = conn.createStatement();
                stmt.execute("SHUTDOWN");
                stmt.close();
                conn.close();
                stmt=null;
                conn =null;
                connState=false;
            } catch(SQLException e) {
                connState=false;
                stmt=null;
                conn =null;
                System.out.println("Disconnecting ERROR:\t" + e);
            }    
        }