How to Correctly Split a Java String Using a Dot (.) as the Delimiter?

Java String Splitting with "." (Dot)

In Java, the split() method is used to divide a string into substrings based on a specified delimiter. However, when attempting to split a string on the literal dot character '.', an ArrayIndexOutOfBoundsException may be thrown.

To illustrate this issue, consider the following code:

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

In the above code, the intention is to remove the file extension by splitting the filename on the dot. However, executing this code will result in an exception.

Conversely, the following code works correctly:

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

This is due to the fact that the split() method interprets '.' as a wildcard character, which matches any character in the string. To split on the literal dot, it is necessary to escape it using a backslash:

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

By escaping the dot, we indicate that we want to split on the literal character, not the wildcard. It's important to note that the backslash character is itself a special character in regex, so it also needs to be escaped using another backslash.

Additionally, when splitting on a dot, it's crucial to account for the edge case where the filename is empty or only consists of a dot. If you attempt to split such a string without using the limit parameter of the split() method, you may encounter an ArrayIndexOutOfBoundsException. To prevent this, use a negative value for the limit parameter:

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

By setting the limit to a negative value, you disable the removal of trailing blanks from the resulting array, ensuring that you always get a valid index even for empty or single-character strings.

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