Issue

import java.sql.*;
import javax.swing.JOptionPane;

public class Uppgift3 {

	public static void main(String[] args) throws SQLException {
		Connection connect = null;
		PreparedStatement preState = null;
		ResultSet result = null;

		try {

			connect = DriverManager.getConnection("jdbc:mysql://localhost/Skola", "Zaher", "hej123");
			preState = connect.prepareStatement("SELECT Betyg FROM BetygVarde WHERE Varde=(SELECT ROUND(AVG(BetygVarde.Varde),0) FROM KursBetyg INNER JOIN BetygVarde ON KursBetyg.Betyg = BetygVarde.Betyg WHERE Kurskod= ?)");
			preState.setString(1, JOptionPane.showInputDialog("Välj Kurs"));
			preState.executeQuery();
			while (result.next()) {
				System.out.println(result.getString("Kurskod"));
			}

		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			result.close();
			preState.close();
			connect.close();
		}

	}

}