Java String Splitting: Why Does `split(\'.\')` Throw an `ArrayIndexOutOfBoundsException`?

Java String Split with ""." (Dot)

Problem:

Why does the following code throw an ArrayIndexOutOfBoundsException when attempting to split on a dot, but works when splitting on a slash:

String filename = "D:/some folder/001.docx";
String extensionRemoved = filename.split(".")[0];

versus:

String driveLetter = filename.split("/")[0];

Solution:

To split on a literal dot, the dot character must be escaped to avoid treating it as a regex pattern (any character):

String extensionRemoved = filename.split("\.")[0];

The double backslash (\) is necessary to create a single backslash in the regex string.

Additionally, an edge case occurs when the input string is just a dot (".") because splitting it on a dot results in an empty array. To prevent an ArrayIndexOutOfBoundsException in this case, use the overloaded split(regex, limit) method with a negative limit to disable the removal of trailing blanks:

String extensionRemoved = filename.split("\.", -1)[0];

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