final是修饰符的一种
1.意思是最终的
2.final可以修饰：类（内部类，外部类）、变量（成员变量（类变量、实例变量）、局部变量）、方法（静态方法和非静态方法）
3.它修饰后有什么不同
-修饰类：表示这个类不能被继承了，可以称为“太监类”
例如：String System Math
-修饰方法：表示这个方法不能被重写
-修饰变量：表示这个变量的值不能被修改，即我们说的“常量”
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