I have some JPG files that need to be replaced at runtime with a JFIF standardized version of themselves (we are using a vendor that gives us JPG that do not have proper headers so they don't work in certain applications)... I am able to create a new file from the existing image, then get a buffered image from that file and write the contents right back into the file without having to delete it and it works...

imageSrcFolder.eachFileMatch ( ~/.*\.jpg/, {
    BufferedImage bi = ImageIO.read( it )
    ImageIO.write( bi, "jpg", it )
});

The question I have is why? Why doesn't the file end up doubled in size? Why don't I have to delete it first? Why am I able to take a file object to an existing file and then treat it as if it were a brand new one? It seems that what I consider to be a "file" is not what the File object in java actually is, or else this wouldn't work at all.

My code does exactly what I want it to do, but I'm not convinced it always will... it just seems way too easy