public Object clone() {
Topic t;
Set<Proposal> proposals = new HashSet<Proposal>();
t = new Topic(getTitle(), getDescription(), getCreationDate());
t.setId(getId());
t.setProject((Project) getProject().clone());
t.setUser((User) getUser().clone());
for (Proposal p : getProposals()) proposals.add((Proposal) p.clone());
t.setProposals(proposals);
return t;
}
