How to use @IdClass annotation with composite key

Question

Someone could please share an example of two entities working on a Master-Detail pattern for EclipseLink (JPA 2.1) using composite key with @IdClass

Answer 1

Here is the example from the documentation

    public class EmployeePK implements Serializable {

     private long empId;
     private long department;

     public EmployeePK() {
     }

     public long getEmpId() {
         return this.empId;
     }

     public void setEmpId(long empId) {
         this.empId = empId;
     }

     public long getDepartment() {
         return this.department;
     }

     public void setDepartment(long department) {
         this.department = department;
     }

     public int hashCode() {
         return (int)this.empId.hashCode();
     }

     public boolean equals(Object obj) {
         if (obj == this) return true;
         if (!(obj instanceof EmployeePK)) return false;
         EmployeePK pk = (EmployeePK) obj;
         return pk.empId.equals(this.empId) && pk.department.equals(this.department);
     }
}

and

@IdClass(EmployeePK.class)
@Entity
public class Employee implements Serializable{

   @Id
   long empId;
   @Id
   @ManyToOne
   Department department;
   ...
}