+-----------+----+--------+
| userName  | id |  pass  |
+-----------+----+--------+
| admin     |  1 |  admin |
| user      |  2 |  pass  |
| chuchelo  |  3 |  elli  |
+-----------+----+--------+

class UserLogin {
    String name;
    String pass;

    public UserLogin() {
    }

    public void login()  {
        BufferedReader reader = null;
        try{
            reader = new BufferedReader(new InputStreamReader(System.in));

            System.out.println("user name: ");
            name = reader.readLine();

            System.out.println("pass: ");
            pass = reader.readLine();
       } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if (reader != null)
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
        }
    }

UserLogin user = new UserLogin();
user.login();
try (Connection connect = MyConnection.getConnection()){
    Statement statement = connect.createStatement();
    String query = "SELECT userName, id, pass FROM users WHERE userName='" + user.name + "' AND pass = '" + user.pass + "'";
    System.out.println(query);
    ResultSet resultSet = statement.executeQuery(query);

    while (resultSet.next()){
        System.out.printf("User: id=%d name=%s pass=%sn",
                resultSet.getInt("id"),
                resultSet.getString("userName"),
                resultSet.getString("pass"));
    }
    MyConnection.closeConnect();
} catch (SQLException e) {
    e.printStackTrace();
}

user name: admin
pass: admin

User: id=1 name=admin pass=admin

SELECT userName, id, pass FROM users WHERE userName='admin' AND pass = 'admin'

user name: admin' or'1'='1
pass: blabla

User: id=1 name=admin pass=admin

SELECT userName, id, pass FROM users WHERE userName='admin' or'1'='1' AND pass = 'blabla'

UserLogin user = new UserLogin();
user.login();
try (Connection connect = MyConnection.getConnection()){
    String query = "SELECT userName, id, pass FROM users WHERE userName=? AND pass=?";
    PreparedStatement statement = connect.prepareStatement(query);
    statement.setString(1, user.name);
    statement.setString(2, user.pass);
    System.out.println(statement);
    ResultSet resultSet = statement.executeQuery();

    while (resultSet.next()){
        System.out.printf("User: id=%d name=%s pass=%sn",
        resultSet.getInt("id"),
        resultSet.getString("userName"),
        resultSet.getString("pass"));
    }
    MyConnection.closeConnect();
} catch (SQLException e) {
    e.printStackTrace();
}

user name: user
pass: pass
User: id=2 name=user pass=pass
Запрос:
SELECT userName, id, pass FROM users WHERE userName='user' AND pass='pass'

user name: user' or'1'='1
pass: inject

SELECT userName, id, pass FROM users WHERE userName='user' or'1'='1' AND pass='inject'