在Java中，我们看到很多地方可以使用final关键字，但它的使用并不常见。
例如:
String str = "abc";
System.out.println(str);
在上面的例子中，str可以是final，但通常不使用。
当一个方法永远不会被覆盖时，我们可以使用final关键字。类似地，类不会被继承。
在任何或所有这些情况下使用final关键字真的能提高性能吗?如果是，那该怎么做?请解释一下。如果final的正确使用确实关系到性能，那么Java程序员应该养成什么样的习惯才能最好地利用这个关键字呢?
当前回答
我不是专家，但我认为你应该在类或方法中添加final关键字，如果它不会被覆盖并留下变量。如果有任何方法来优化这样的东西，编译器会为你做。
其他回答
通常不会。对于虚方法，HotSpot会跟踪该方法是否实际被重写，并且能够在假定某个方法没有被重写的情况下执行优化，例如内联——直到它加载一个重写该方法的类，这时它可以撤销(或部分撤销)那些优化。
(当然，这是假设你正在使用HotSpot -但它是迄今为止最常见的JVM，所以…)
在我看来，使用final应该基于清晰的设计和可读性，而不是出于性能考虑。如果您出于性能原因想要更改任何内容，那么应该在修改最清晰的代码之前执行适当的度量——这样您就可以决定以较差的可读性/设计换取额外的性能是否值得。(根据我的经验，这几乎不值得;YMMV)。
EDIT: As final fields have been mentioned, it's worth bringing up that they are often a good idea anyway, in terms of clear design. They also change the guaranteed behaviour in terms of cross-thread visibility: after a constructor has completed, any final fields are guaranteed to be visible in other threads immediately. This is probably the most common use of final in my experience, although as a supporter of Josh Bloch's "design for inheritance or prohibit it" rule of thumb, I should probably use final more often for classes...
根据IBM的说法——它不用于类或方法。
http://www.ibm.com/developerworks/java/library/j-jtp04223.html
注意:不是java专家
如果我没有记错我的java，使用final关键字几乎没有办法提高性能。 我一直知道它的存在是为了“好代码”——设计和可读性。
I cannot say it is uncommon because as far as I know it is the only way of declaring a constant in java. As a javascript developer, I know how important the keyword constant is. If you are working in production level, and you have values that can never be changed even accidentally by other coders, values such as SSN number or even names. Then you have to use the final keyword to declare variables. Sometimes it can be very troublesome if certain classes can be inherited. Because if many people are working in a team someone can inherit a class, extend it and even make changes to the variables and methods of the parent class. This can be stopped with the keyword final because even static variables can be changed unless the final keyword is used. As far as your question is concerned I do not think the final keyword can affect the performance of the code, but it can definitely prevent human errors by making sure that other team members do not accidentally modify anything that needs to remain constant.
我不是专家，但我认为你应该在类或方法中添加final关键字，如果它不会被覆盖并留下变量。如果有任何方法来优化这样的东西，编译器会为你做。
