Java – Why would one mark local variables and method parameters as “final” in Java?


In Java, you can qualify local variables and method parameters with the final keyword.

public static void foo(final int x) {
  final String qwerty = "bar"; 

Doing so results in not being able to reassign x and qwerty in the body of the method.

This practice nudges your code in the direction of immutability which is generally considered a plus. But, it also tends to clutter up code with "final" showing up everywhere. What is your opinion of the final keyword for local variables and method parameters in Java?

Best Solution

You should try to do this, whenever it is appropriate. Besides serving to warn you when you "accidentally" try to modify a value, it provides information to the compiler that can lead to better optimization of the class file. This is one of the points in the book, "Hardcore Java" by Robert Simmons, Jr. In fact, the book spends all of its second chapter on the use of final to promote optimizations and prevent logic errors. Static analysis tools such as PMD and the built-in SA of Eclipse flag these sorts of cases for this reason.