一. 继承的特点
1. 继承的特点：
- 子类继承父类
// 从事务的特征来说，子类会继承父类的所有特征
// 从代码操作的角度来说，父类中私有的属性，方法在子类中是不能直接使用的
- 子类继承父类时，构造器是不能被继承的
- 子类继承父类时，在子类的构造器中一定要去调用父类的构造器，默认情况下是调用调用父类的无参构造；如果父类没有无参构造，那么在子类的构造器首行，必须手动调用父类的有参构造
- java中只支持单继承，即一个java类中只能有一个直接父类
- java支持多层继承，即父类还可以有父类
- 一个java类可以同时有很多个子类
- 子类可以扩展父类没有的属性、方法
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