create or replace package test_system is
    type ref_cursor is ref cursor;
procedure demo_show_students(p_gpa IN STUDENTS.gpa%TYPE,p_ref_cursor  OUT ref_cursor );
end test_system;
/

create or replace package body test_system is
procedure demo_show_students(p_gpa IN STUDENTS.gpa%TYPE,p_ref_cursor   OUT ref_cursor )
is
v_sql_str varchar2(4000);
begin
v_sql_str:='select sid,firstname,lastname,status,gpa,email from students where gpa = p_gpa';
open p_ref_cursor for v_sql_str;
end demo_show_students;
end test_system;

import java.sql.*;

import oracle.jdbc.OracleTypes;

public class ShowStudents {

public void showStudents() {

    try {

        // Connection to Oracle server
        OracleDataSource ds = new oracle.jdbc.pool.OracleDataSource();
        ds.setURL("jdbc:oracle:thin:@localhost:1521:xe");
        Connection conn = ds.getConnection("*****", "*****");

        String val = '4'+"";
        CallableStatement cs = conn.prepareCall("{call
        test_system.demo_show_students(?,?)}");
        cs.setString(1, val);

        cs.registerOutParameter(2, OracleTypes.CURSOR);
        cs.execute();
        ResultSet rs = (ResultSet)cs.getObject(2);

        while (rs.next()) {
            System.out.println(rs.getString(1) + "t" +
                rs.getString(2) + "t" + rs.getString(3) +
                rs.getString(4) +
                "t" + rs.getDouble(5) + "t" +
                rs.getString(6));
        }


        cs.close();

    } catch (SQLException ex) {
        System.out.println("n*** SQLException caught ***n");
        ex.printStackTrace();
    } catch (Exception e) {
        System.out.println("n*** other Exception caught ***n");
    }
}
}



Exception :

*** SQLException caught ***
ORA-00904: "P_GPA": invalid identifier
ORA-06512: at "PROJECT2.TEST_SYSTEM", line 7
ORA-06512: at line 1