Two entities relates as many to many (Course and Student).
During deployment it throws:

Caused by: org.hibernate.MappingException: Could not determine type for: java.util.Collection, for columns: org.hibernate.mapping.Column(students)]

Both sides using Generics.
Here is the latest code:

@Entity(name = "StudentUni")
public class Student implements Serializable {
private int id;
private String name;
private Collection<Course> courses = new ArrayList<Course>();

public Student()

{ id = (int) System.nanoTime(); }

@Id
public int getId() { return id; }

public void setId(int id) { this.id = id; }

public String getName() { return name; }

public void setName(String name) { this.name = name; }

@ManyToMany
public Collection<Course> getCourses() { return courses; }

public void setCourses(Collection<Course> courses) { this.courses = courses; }
}

@Entity(name = "CourseUni")
public class Course implements Serializable {
private int id;
private String courseName;
private Collection<Student> students = new ArrayList<Student>();

public Course(){ id = (int) System.nanoTime(); }

@Id
public int getId()

{ return id; }

public void setId(int id)

{ this.id = id; }

public String getCourseName()

{ return courseName; }

public void setCourseName(String courseName)

{ this.courseName = courseName; }

@ManyToMany(mappedBy = "courses")
public Collection<Student> getStudents()

{ return students; }

public void setStudents(Collection<Student> students)

{ this.students = students; }

}