import java.sql.*;

public class Labb {
    public static void main(String[] args) {
        try
        {
          // create the mysql database connection
          String myDriver = "com.mysql.jdbc.Driver";

          //specify the database to connect
          String myUrl = "jdbc:mysql://localhost/studentcontract";

          //connect to the database
          Class.forName(myDriver);
          Connection conn = DriverManager.getConnection(myUrl, "root", "");

          // create the SQL select statement.

                  String query = "SELECT * FROM student";

          // create the java statement
          Statement st = conn.createStatement();

          // execute the query; the result of the execution is stored in an object of ResultSet class
          ResultSet rs = st.executeQuery(query);

          // there can be more than one result. so, we have to go through each data. in each round, only one record will be readed.  int count=0;
                 int count=0;
                 double sum =0;
          while (rs.next())
          {
                      double height = (double) rs.getDouble("height");
                      sum=sum+height;
                      count++;
          }
              sum=sum/count;

              System.out.print(sum);
          st.close();
        }
        catch (Exception e)
        {
          System.err.println("Got an exception! ");
          System.err.println(e.getMessage());
          e.printStackTrace();
        }

    }

}