This item is
similar in nature to Item 13, “Minimize the accessibility of classes and
members.” By minimizing the scope of local variables, you increase the
readability and maintainability of your code and reduce the likelihood of
error.
The most
powerful technique for minimizing the scope of a local variable is to declare
it where it is first used.
Nearly every
local variable declaration should contain an initializer. If you don’t
yet have enough information to initialize a variable sensibly, you should
postpone the declaration until you do. One exception to this rule concerns trycatch statements.
Loops present
a special opportunity to minimize the scope of variables. The for loop, in both its traditional and for-each
forms, allows you to declare loop variables, limiting
their scope to the exact region where they’re needed. Therefore, prefer for loops to while
loops, assuming the
contents of the loop variable aren’t needed after the loop terminates.
The for loop has one more advantage over the while loop: it is shorter, which enhances
readability.
A final
technique to minimize the scope of local variables is to keep methods
small and focused. If you combine two activities in the same method, local
variables relevant to one activity may be in the scope of the code performing
the other activity. To prevent this from happening, simply separate the method
into two: one for each activity.
Reference: Effective Java 2nd Edition by Joshua Bloch
