听起来，反对使用最后一个关键字的最大论点之一是“这是不必要的”，而且它“浪费空间”。

如果我们承认“final”的许多好处，同时承认它需要更多的输入和空间，我认为Java应该默认将变量设置为“final”，并且如果编码器想要的话，就要求将变量标记为“mutable”。

有效的Java有一个条目写着“偏爱不可变对象”。将字段声明为final可以帮助您在这方面迈出一小步，但是对于真正的不可变对象来说，当然还有更多的事情要做。

如果您知道对象是不可变的，那么可以在多个线程/客户端之间共享它们以供读取，而无需担心同步问题，并且更容易推断程序的运行方式。

我很少在方法或类上使用final，因为我喜欢允许人们重写它们。

否则，我只使用finally如果它是一个公共/私有静态最终类型SOME_CONSTANT;

I have to read a lot of code for my job. Missing final on instance variables is one of the top things to annoy me and makes understanding the code unnecessarily difficult. For my money, final on local variables causes more clutter than clarity. The language should have been designed to make that the default, but we have to live with the mistake. Sometimes it is useful particularly with loops and definite assignment with an if-else tree, but mostly it tends to indicate your method is too complicated.

Final显然应该用在常量上，并加强不可变性，但在方法上还有另一个重要的用途。

Effective Java在这方面有一个完整的项目(项目15)，指出了意外继承的陷阱。实际上，如果您没有为继承而设计和记录您的类，那么从它继承可能会带来意想不到的问题(该项目提供了一个很好的例子)。因此，建议在不打算继承的任何类和/或方法上使用final。

That may seem draconian, but it makes sense. If you are writing a class library for use by others then you don't want them inheriting from things that weren't designed for it - you will be locking yourself into a particular implementation of the class for back compatibility. If you are coding in a team there is nothing to stop another member of the team from removing the final if they really have to. But the keyword makes them think about what they are doing, and warns them that the class they are inheriting from wasn't designed for it, so they should be extra careful.

Final应该总是用于常量。当定义变量的规则很复杂时，它甚至对于短期存在的变量(在单个方法中)也很有用。

例如:

final int foo;
if (a)
    foo = 1;
else if (b)
    foo = 2;
else if (c)
    foo = 3;
if (d)        // Compile error:  forgot the 'else'
    foo = 4;
else
    foo = -1;