org.hibernate.MappingException: Unknown entity: com.Course
   at org.hibernate.impl.SessionFactoryImpl.getEntityPersister(SessionFactoryImpl.java:550)
   at org.hibernate.impl.SessionImpl.getEntityPersister(SessionImpl.java:1338)
   at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:98)
   at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
   at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
   at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
   at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
   at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
   at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:535)
   at org.hibernate.impl.SessionImpl.save(SessionImpl.java:523)
   at org.hibernate.impl.SessionImpl.save(SessionImpl.java:519)

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.util.HibernateUtil;

public class ExecutingFile {

    public static void main(String[] args) {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction transaction = null;
        try {
            transaction = session.beginTransaction();
            Course course = new Course();
            course.setCourseId(Long.MIN_VALUE);
            course.setCourseName("Math");
            Student student1 = new Student(Long.MAX_VALUE, "Mohen", course);
            session.save(course);
            session.save(student1);
            transaction.commit();
        } catch (HibernateException e) {
            transaction.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }
    }
}

import java.io.Serializable;
import java.util.Collection;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlTransient;

/**
*
* @author super00000
*/
@Entity
@Table(name = "course")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "Course.findAll", query = "SELECT c FROM Course c"),
    @NamedQuery(name = "Course.findByCourseId", query = "SELECT c FROM Course c WHERE c.courseId = :courseId"),
    @NamedQuery(name = "Course.findByCourseName", query = "SELECT c FROM Course c WHERE c.courseName = :courseName")})
public class Course implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @Basic(optional = false)
    @Column(name = "course_id")
    private Long courseId;
    @Column(name = "course_name")
    private String courseName;
    @OneToMany(mappedBy = "studentCourse")
    private Collection<Student> studentCollection;

    public Course() {
    }

    public Course(Long courseId) {
        this.courseId = courseId;
    }

    public Long getCourseId() {
        return courseId;
    }

    public void setCourseId(Long courseId) {
        this.courseId = courseId;
    }

    public String getCourseName() {
        return courseName;
    }

    public void setCourseName(String courseName) {
        this.courseName = courseName;
    }

    @XmlTransient
    public Collection<Student> getStudentCollection() {
        return studentCollection;
    }

    public void setStudentCollection(Collection<Student> studentCollection) {
        this.studentCollection = studentCollection;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (courseId != null ? courseId.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof Course)) {
            return false;
        }
        Course other = (Course) object;
        if ((this.courseId == null && other.courseId != null) || (this.courseId != null && !this.courseId.equals(other.courseId))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "com.Course[ courseId=" + courseId + " ]";
    }
   
}