Login button

 private void LoginBtnActionPerformed(java.awt.event.ActionEvent evt) {
        // TODO add your handling code here:
        user=UserField.getText();
        password=PasswordField.getText();
        DBCollection coll = db.getCollection("user");


        BasicDBObject andQuery = new BasicDBObject();
        List<BasicDBObject> obj = new ArrayList<BasicDBObject>();
	obj.add(new BasicDBObject("user", user));
	obj.add(new BasicDBObject("password", password));
	andQuery.put("$and", obj);

         DBCursor cursor = coll.find(andQuery);
         DBObject result =null;

	while (cursor.hasNext())
        {
            result=cursor.next();
        }

         if(result!=null){

          String state=result.get("state").toString();



            if(state.equals("parent")){
                 String firstname=result.get("firstname").toString();
                 String lastname=result.get("lastname").toString();
                 Parent parent=new Parent(conn,db,firstname,lastname,this);
                 parent.setSize(frame.getSize());
                 frame.add(parent);
                 UserField.setText("");
                 PasswordField.setText("");
                 this.setVisible(false);

            }else if(state.equals("teacher")) {
                 String firstname=result.get("firstname").toString();
          String lastname=result.get("lastname").toString();
                Teacher teacher=new Teacher(conn,db,firstname,this,frame);
                teacher.setSize(frame.getSize());
                frame.add(teacher);
                 UserField.setText("");
                 PasswordField.setText("");
                 this.setVisible(false);

            }else{
                Admin admin=new Admin(conn,db,this,this.frame);
                admin.setSize(frame.getSize());
                 UserField.setText("");
                 PasswordField.setText("");
                frame.add(admin);
                this.setVisible(false);
            }



               }else{
                  JOptionPane.showMessageDialog(null, "wrong username or password , try  again !");
                  UserField.setText("");
                  PasswordField.setText("");
               }

    }