public Letter<?> createRandomLetter() {
		Letter<?> letter;
		Inhabitant sender = this.inhabitants[r.nextInt(100)] ;
		Inhabitant receiver = this.inhabitants[r.nextInt(100)] ;
		Letter<TextContent> lettre = new SimpleLetter<TextContent>(sender, receiver, new TextContent("Bonjour tu vas bien ?")) ;
		switch (r.nextInt(4)) {
		case 0:
				letter = new PromissoryNote<MoneyContent>(sender, receiver, new MoneyContent(10)) ;
				break;
		case 1:
				letter = new SimpleLetter<TextContent>(sender, receiver, new TextContent("Bonjour tu vas bien ?")) ;
				break ;
		case 2:
				letter = new UrgentLetter<Letter<TextContent>>(sender, receiver, lettre);
				break ;
		default:
				letter = new RegisteredLetter<Letter<TextContent>>(sender, receiver, lettre);
				break ;
		}	
		return letter;
	}