Why does this split() fail?

Question

I'm trying to get the extension of a filename, but for some reason I can't make split work:

System.out.println(file.getName()); //gNVkN.png
System.out.println(file.getName().split(".").length); //0

What am I doing wrong?

Answer 1

split() takes a regular expression (See split(java.lang.String)), not a separator string to split by. The regular expression "." means "any single character" (See regex), so it will split on anything leaving nothing in you list. To split on a literal dot use:

file.getName().split("\\.")// \. escapes . in regex \\ escapes \ in Java.String

In general, you can use Pattern.quote(str) to obtain a regular expression that matches str literally. (suggested by ramon)

file.getName().split(Pattern.quote("."))

Answer 2

Maybe you should reread the api-doc for split(java.lang.String)

The string you pass in is a regex.

Try using

split("\\.")

You need the double backslash because \. is an invalid escape in a Java-string. So you need to escape the backslash itself in the javastring.