@idclass vs @embedable

1. @Idclass

@Entity @IdClass(ProjectId.class)
public class Project {
    @Id int departmentId;
    @Id long projectId;
     :
}


Class ProjectId {
    int departmentId;
    long projectId;
}

2.@embedable

@Entity
public class Project {
    @EmbeddedId ProjectId id;
     :
}


@Embeddable
Class ProjectId {
    int departmentId;
    long projectId;
}

Ref: https://www.objectdb.com/java/jpa/entity/id