public boolean store(String file){
		Iterator it = this.keySet().iterator();
		StringBuffer sb = new StringBuffer();
		
		String[]  datelist = new String[this.size()];
		int index = 0 ;
		while(it.hasNext()){
			datelist[index] = (String) it.next();
			index++ ;
		}
		
		java.util.Arrays.sort(datelist);
		
		
		for(int i = 0 ; i < index;i++){
			Checkin ci = (Checkin)this.get(datelist[i]);
			sb.append(ci.checkin);
			sb.append(";");
			sb.append(ci.checkout);
			sb.append("\n");
		}
		sb.toString();
		File f = new File(file);
		if(!f.exists()){
			try {
				f.createNewFile();
			} catch (IOException e) {				
				e.printStackTrace();
				return false;
			}
		}
		
		try {
			FileOutputStream fos = new FileOutputStream(f);
			fos.write(sb.toString().getBytes());
			fos.flush();
			fos.close();
			return true ;
		} catch (FileNotFoundException e) {		
			e.printStackTrace();
			return false;
		} catch (IOException e) {			
			e.printStackTrace();
			return false;
		}
	}