public void push(String stack, E element) {
		synchronized(lock) {
			if(STACK1.equals(stack)) {
				array[tail1++] = element;
				if(tail1 >= array.length/3-1) {
					resize();
				}
			} else if (STACK2.equals(stack)) {
				array[tail2--] = element;
				if(tail2 <= tail3+1) {
					resize();
				}
			} else if (STACK3.equals(stack)) {
				array[tail3++] = element;
				if(tail3 >= tail2-1) {
					resize();
				}
			}
		}
	}