"non static method cannot be referenced from a static context" JPA Java

Question

I'm getting the "non static method cannot be referenced from a static context" error from this line:

createStudent("stu00001", new Date(631152000000)), "m", "WB", new Type_Name("Bob", "", "Smith"));

How do you form 'Date' properly? I've had a look on the API's and tried different things but I still get an error for date.

package grade_db;

import bean.Student;
import bean.Type_Name;
import bean.University;
import java.util.Date;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
/**
 *
 * @author Sam
 */

public class Main {

EntityManager em;
EntityManagerFactory emf;

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here

        EntityManagerFactory emf = Persistence.createEntityManagerFactory("db/grades.odb");

        EntityManager em;
        em = emf.createEntityManager();

        createStudent("stu00001", new Date(631152000000)), "m", "WB", new Type_Name("Bob", "", "Smith"));

        em.close();
        emf.close();
    }


    public Student createStudent(String student_id, Date dob, String gender, String nationality, Type_Name name){
    Student stu = new Student();
    stu.setDob(dob);
    stu.setGender(gender);
        stu.setName(name);
    stu.setNationality(nationality);

        stu.setCampus_id("cam00001");
        stu.setCourse_id(null);
        stu.setStudent_id(student_id);

    em.persist(stu);
    return stu;
}
}

sigpwned · Accepted Answer · 2013-04-12T19:32:26.247

The problem is that you're trying to call the instance method createStudent() from a static context in main(). If you change your createStudent() method to be static, you should be good to go:

public static Student createStudent(String student_id, Date dob, String gender, String nationality, Type_Name name) {
    // ... And so on 
}

EDIT: OP pointed out that this change alone gives him another error when accessing the variables em and emf. To fix that, you'd need to make those variables static, too:

static EntityManager em;
static EntityManagerFactory emf;

At that point, everything in your class is static. Assuming this is a simple one-off or example -- which I'm comfortable assuming since the class is called Main -- making everything static is just fine. In all, the code would look like this:

package grade_db;

import bean.Student;
import bean.Type_Name;
import bean.University;
import java.util.Date;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
/**
 *
 * @author Sam
 */

public class Main {

    static EntityManager em;
    static EntityManagerFactory emf;

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here

        EntityManagerFactory emf = Persistence.createEntityManagerFactory("db/grades.odb");

        EntityManager em;
        em = emf.createEntityManager();

        createStudent("stu00001", new Date(631152000000)), "m", "WB", new Type_Name("Bob", "", "Smith"));

        em.close();
        emf.close();
    }

    public static Student createStudent(String student_id, Date dob, String gender, String nationality, Type_Name name){
        Student stu = new Student();
        stu.setDob(dob);
        stu.setGender(gender);
        stu.setName(name);
        stu.setNationality(nationality);

        stu.setCampus_id("cam00001");
        stu.setCourse_id(null);
        stu.setStudent_id(student_id);

        em.persist(stu);
        return stu;
    }
}

Thanks! When I do this though I get the same 'non static method' error with "em.persist(stu);" — , Apr 12 '13 at 19:29
Updated the response. Short answer: the variables need to be static, too. — sigpwned, Apr 12 '13 at 19:32
That worked great, thanks. Do you have any advice on calling the method 'createStudent'? I keep getting errors like "insert ;" and date format errors. It should be createStudent(String, Date, String, String, Type_Name) (TypeName is just three strings for first, middle & last name) — , Apr 12 '13 at 19:46

score 2 · Answer 2 · answered Apr 12 '13 at 19:23

2

Make the method

       public static Student createStudent(String student_id, Date dob, String gender, String nationality, Type_Name name){
Student stu = new Student();

static

answered Apr 12 '13 at 19:23

Seid.M

185
7

score 0 · Answer 3 · answered Apr 12 '13 at 19:23

this is because CreateStudent is a member method of an object. Main is static and is not part of an object.

You need to create a new Main object, or make student static in order for this to work.

If you make createStudent static it will work.

public static Student createStudent(String student_id, Date dob, String gender, String nationality, Type_Name name)

"non static method cannot be referenced from a static context" JPA Java

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