I needed to confirm if my understanding is correct around final method arguments. If we leave aside anonymous classes from this discussion,the ONLY reason why I would tag a method argument as final is catch something at compile time,rather than scratching my head over a run-time bug later on. Do I get it correct? Or is there some design paradigm I am missing out?
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3 Answers
It is considered a bad practice to assign values to parameters, from within a method's body:
public void myMethod (String parm) {
parm = "some-value"; // This is very frowned upon
}
Declaring the argument as final ensures that you won't pass compilation if you attempt such practice.
There are no other design factors that I am aware of (that is, other than what you had mentioned regarding anonymous classes etc).
Comments
It doesn't make a difference at runtime. This is provable in the most conclusive way: adding the final modifier doesn't even change the compiled bytecode!
FinalParam.java (before)
class FinalParam {
public static void main(String[] args) {
System.out.println(java.util.Arrays.toString(args));
}
}
$ javac -version
javac 1.7.0_15
$ javac FinalParam.java
$ md5sum FinalParam.class
7ca43ea68179f6191d5bf1de7ba21945
$ rm FinalParam.class
FinalParam.java (after)
class FinalParam {
public static void main(final String[] args) {
System.out.println(java.util.Arrays.toString(args));
}
}
$ javac FinalParam.java
$ md5sum FinalParam.class
7ca43ea68179f6191d5bf1de7ba21945
Comments
This is correct, final helps detect parameter assigment at compile time. However I think it is better to configure compiler to detect this kind of problems. Eg Eclipse has Parameter Assigment setting in Java Compiler Errors/Warnings Preferences.
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