public String bidForAuction(User user, int auctionID, double amount) {
		String answer = "";
		
		synchronized (syncAuctionList) {
			Iterator<Auction> iterator = syncAuctionList.iterator();
			Auction auction;
			
			while (iterator.hasNext()) {
				auction = iterator.next();
				if (auction.getId() == auctionID) {
					if (amount > auction.getHightestAmount()) {
						User oldHighestBidder = auction.getHighestBidder();
						
						auction.setHightestAmount(amount);
						auction.setHighestBidder(user);

						if (!oldHighestBidder.getName().equals("none")) {
							String msg = "!new-bid " + auction.getDescribtion();
							// send UDP- notofication that he has been oberbidden if he is online
							if (oldHighestBidder.isOnline()) {
								try {
									AuctionServer_UDPSocket.getInstamce().sendMessage(oldHighestBidder.getInternetAdress(), oldHighestBidder.getUdpPort(), msg);
								} catch (IOException e) {
									System.out.println("Error: Trying to send UDP- Message to unknown user");
								}
							}
							else {
								// if he is not online store the notification
								oldHighestBidder.storeNotification(msg);
							}
						}
						
						
						return answer = "You successfully bid with " + printHighestAmount(amount) + 
								" on '" + auction.getDescribtion() + "'.";
					}
					else {
						return answer = "You unsuccessfully bid with " + printHighestAmount(amount) + " on '" + 
								auction.getDescribtion() + "'. Current highest bid is " + auction.getHightestAmount() + ".";
					}
				}
			}
			answer = "The Aucion- ID '" + auctionID + "' is unknown!";
		}
		
		return answer;
	}