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Java always makes a copy of parameters before sending them to methods. This means the final doesn't mean any difference for the calling code. This only means that inside the method the variables can not be reassigned.
Classes and MethodsThere are no reported performance benefits of applying final to classes and methods.
Like methods, local variables and parameters need not to be declared final. As others said before, this clutters the code becoming less readable with very little efford for compiler performace optimisation, this is no real reason for most code fragments.
The final keyword does not appear in the class file for local variables and parameters, thus it cannot impact the runtime performance. It's only use is to clarify the coders intent that the variable not be changed (which many consider dubious reason for its usage), and dealing with anonymous inner classes.
There is a lot of argument over whether the final modifier on the method itself has any performance gain since the methods will be inlined by the optimizing compiler at runtime anyway, regardless of the modifier. In this case it should also only be used to restrict the overriding of the method.
The only benefit to a final parameter is that it can be used in anonymous nested classes. If a parameter is never changed, the compiler will already detect that as part of it's normal operation even without the final modifier. It's pretty rare that bugs are caused by a parameter being unexpectedly assigned - if your methods are big enough to need this level of engineering, make them smaller - methods you call can't change your parameters.
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