In Java, should variables be declared at the top of a function, or as they're needed?

Question

I\'m cleaning up Java code for someone who starts their functions by declaring all variables up top, and initializing them to null/0/whatever, as opposed to declaring them a

Answer 1

From the Java Code Conventions, Chapter 6 on Declarations:

6.3 Placement

Put declarations only at the beginning of blocks. (A block is any code surrounded by curly braces "{" and "}".) Don't wait to declare variables until their first use; it can confuse the unwary programmer and hamper code portability within the scope.

void myMethod() {
    int int1 = 0;         // beginning of method block

    if (condition) {
        int int2 = 0;     // beginning of "if" block
        ...
    }
}

The one exception to the rule is indexes of for loops, which in Java can be declared in the for statement:

for (int i = 0; i < maxLoops; i++) { ... }

Avoid local declarations that hide declarations at higher levels. For example, do not declare the same variable name in an inner block:

int count;
...
myMethod() {
    if (condition) {
        int count = 0;     // AVOID!
        ...
    }
    ...
}