file names : Java Glossary

by Roedy Green ©1996-2009 Canadian Mind Products
index page for letter ⇒ punctuation 0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z (all)

file names

Java lets you use any filename the current OS supports. However if your program uses any filenames not supplied by the end user, you want ones that will work on every conceivable platform. Consider avoiding names like this:

../ ..\ ./ .\ .. / \ * [ ] { } : ? ^ | " & % : ; ' < > = + or with those strings embedded as literal filenames. These have special meaning in script languages. Obviously you must use / \ in fully qualified names, and ../ in names you pass to the OS, but you don’t use them in the directory and filename pieces in the disk directory.
! and ` have special meaning in some Unix shells.
lead - : the filename later could be misconstrued as an option switch.
lead . : in Unix variants this means hidden.
Control characters or unprintable characters.
Filenames with spaces are a bear on the command line, requiring special quoting which often gets confused. Never use leading or trailing spaces since they are often automatically trimmed.
$ ~ @ _ are often reserved by progammers for special meaning, especially lead or trailing. It is best to avoid casual use.
To be completely safe, you would have to avoid all punctuation and non-ASCII 7 alphabetics. If you must use some punctuation the safest to use are # _ -.

Case Sensitivity

In some platforms the precise case of each letter matters and on others it does not. For example Vista does not care, but Linux does. On a case sensitive system, strawberry.txt and Strawberry.txt are two separate files. This can lead to confusion when files are manipulated both in the program and externally with a GUI explorer or command line shell.

My rule of thumb is to keep all filenames lower case (easier to type), easier to remember, with the exception of the *.java and *.class files which must follow Java conventions.

Sort Order

When you are naming a group of similar files, think about how they will sort alphabetically. Files named with the pattern receipts-YYYY-MM-DD.log e.g. receipts-2008-12-31.log will sort more sensibly than receipts-MM-DD-YYYY.log. Even safer would be to use the pattern receiptYYYYMMDD.log.

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