Question

(Without including any external libraries.)

What’s the most efficient way to remove the extension of a filename in Java, without assuming anything of the filename?

Some examples and expected results:

• folder > folder
• hello.txt > hello
• read.me > read
• hello.bkp.txt > hello.bkp
• weird..name > weird.
• .hidden > .hidden

(or should the last one be just hidden?)

Edit: The original question assumed that the input is a filename (not a file path). Since some answers are talking about file paths, such functions should also work in cases like:

• rare.folder/hello > rare.folder/hello

This particular case is handled very well by Sylvain M’s answer.

Answer 1

I’m going to have a stab at this that uses the two-arg version of lastIndexOf in order to remove some special-case checking code, and hopefully make the intention more readable. Credit goes to Justin ‘jinguy’ Nelson for providing the basis of this method:

public static String removeExtention(String filePath) {
    // These first few lines the same as Justin's
    File f = new File(filePath);

    // if it's a directory, don't remove the extention
    if (f.isDirectory()) return filePath;

    String name = f.getName();

    // Now we know it's a file - don't need to do any special hidden
    // checking or contains() checking because of:
    final int lastPeriodPos = name.lastIndexOf('.');
    if (lastPeriodPos <= 0)
    {
        // No period after first character - return name as it was passed in
        return filePath;
    }
    else
    {
        // Remove the last period and everything after it
        File renamed = new File(f.getParent(), name.substring(0, lastPeriodPos));
        return renamed.getPath();
    }
}

To me this is clearer than special-casing hidden files and files that don’t contain a dot. It also reads clearer to what I understand your specification to be; something like “remove the last dot and everything following it, assuming it exists and is not the first character of the filename”.

Note that this example also implies Strings as inputs and outputs. Since most of the abstraction requires File objects, it would be marginally clearer if those were the inputs and outputs as well.