Pool implemenation

Pool.java

  private static abstract class Pool<T> {
    private final Deque<T> pool;

    Pool(int initialSize) {
      pool = new ArrayDeque<T>(initialSize);
      for (int i = 0; i < initialSize; i++) {
        pool.addLast(newObject());
      }
    }

    T obtain() {
      return pool.isEmpty() ? newObject() : pool.removeLast();
    }

    void restore(T instance) {
      pool.addLast(instance);
    }

    protected abstract T newObject();
  }