Question

Suppose, I have a method with a parameter of Object type.
The method returns nothing – void.

First it checks whether the parameter is not null (or any other check, like objectParam.isEnabled())

if (objectParam.isEnabled()) {
    // ok
}

Now, if the condition is satisfied, I need local variables. If it’s not, then I don’t need any variables.

WHERE SHOULD I define them? Inside the “if scope” or just after the method header?

Of course, I can do it wherever I like, but which way should be a better practice?

Answer 1

I believe it’s best practice to declare a variable as late as you can, in the most tightly nested scope that you can, ideally at the point where it’s initialized with a useful value.

That makes it clearer where and how it’s going to be used – when you’re looking at the code where it’s used, you won’t have to look up very far to see the declaration.

In this particular case I disagree with the official Java Style Guide – and so does Josh Bloch. From Effective Java, 2nd edition, item 45:

The most powerful technique for minimizing the scope of a local variable is to declare it where it is first used.

So if you don’t need the variable until you’ve executed a few other statements, don’t declare it until that point.