public void checkStairs() {
		levels = this.getLevels();
		for (int level = 0; level < 9; level++) {
			if (levels[level] != null) {
				char[][] currLevel = levels[level].getLevel();
				for (int i = 0; i < currLevel.length; i++) {
					for (int j = 0; j < currLevel.length; j++) {
						char element = currLevel[i][j];
						int stair = -1;
						try {
							stair = Integer.parseInt(element + "");
							if(levels[stair]!=null){
							if(levels[stair].getStairs()[level]==null){
								System.out.println("invalid stairs");
								System.exit(0);
							}
							}
						} catch (Exception e) {

						}
					}
				}
			}
		}
	}