java-类初始化与实例初始化
内存执行顺序：
1. 先完成父类的类初始化
2. 再完成子类的类初始化
3. 父类的实例初始化
4. 子类的实例初始化
When nothing seems to help, I go look at a stonecutter hammering away at his rock, perhaps a hundred times without as much as a crack showing in it. Yet at the hundred and first blow it will split in two, and I know it was not that blow that did it, but all that had gone before. -- Jacob Riis
