CallableStatement in Java

import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.Types;
 
public class Callable {
    public static void main(String[] args) throws Exception {
        try (Connection con =
                 DriverManager.getConnection("jdbc:h2:mem:school");
             Statement st = con.createStatement()) {
            st.execute("CREATE TABLE student ("
                + "id INT PRIMARY KEY, name VARCHAR(50), marks INT)");
            st.executeUpdate("INSERT INTO student VALUES "
                + "(1, 'Navika', 91), (2, 'Srihitha', 84), (3, 'Advitha', 34)");
 
            // Two routines stored in the database. H2 writes them in Java;
            // MySQL, PostgreSQL and Oracle use their own procedure languages.
            st.execute("CREATE ALIAS grade_for AS $$ "
                + "String gradeFor(int marks) { "
                + "return marks >= 90 ? \"A\" : marks >= 35 ? \"B\" : \"F\"; "
                + "} $$");
            st.execute("CREATE ALIAS students_above AS $$ "
                + "java.sql.ResultSet above(java.sql.Connection c, int min) "
                + "throws java.sql.SQLException { "
                + "java.sql.PreparedStatement ps = c.prepareStatement("
                + "\"SELECT name, marks FROM student "
                + "WHERE marks >= ? ORDER BY marks DESC\"); "
                + "ps.setInt(1, min); return ps.executeQuery(); } $$");
 
            // 1. A function: one value comes back through the first "?".
            try (CallableStatement cs =
                     con.prepareCall("{? = call grade_for(?)}")) {
                cs.registerOutParameter(1, Types.VARCHAR);
                for (int marks : new int[] {91, 60, 20}) {
                    cs.setInt(2, marks);
                    cs.execute();
                    System.out.println(marks + " -> grade " + cs.getString(1));
                }
            }
 
            // 2. A procedure that returns rows.
            try (CallableStatement cs =
                     con.prepareCall("{call students_above(?)}")) {
                cs.setInt(1, 80);
                try (ResultSet rs = cs.executeQuery()) {
                    while (rs.next()) {
                        System.out.println(rs.getString("name") + " "
                            + rs.getInt("marks"));
                    }
                }
            }
        }
    }
}

DELIMITER //
CREATE PROCEDURE grade_for(IN p_marks INT, OUT p_grade VARCHAR(1))
BEGIN
    SET p_grade = CASE WHEN p_marks >= 90 THEN 'A'
                       WHEN p_marks >= 35 THEN 'B' ELSE 'F' END;
END //
DELIMITER ;