What type of File is created when we create new File without the extension?

In java, when we create a file, we create files using the name of the extension. For example :

File file = new File("D:/light.txt");

I would like to know what type of file format do we get when we create a file without the file extension type. For example : 

File file = new File("D:/light");
Jon Skeet
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This answer assumes you're doing more than just creating a File object - that you're actually creating a file on the file system. (A File object is just a logically representation of a file system entry which may or may not exist.) If you're really just creating a File object, read EJP's answer - at that point, you've basically just got a name. That doesn't have a "type" or a "format".

The extension is just part of the name. The operating system may try to use that to display a different icon, or launch a specific application when you double-click on the icon, or whatever - but it's really just part of the name.

Fundamentally, a file consists of:

  • The name you specify when you create it
  • The bytes you write in it
  • Metadata such as access control

Unless you deliberately add metadata, it's typically just inherited (default permissions etc).

You can write any data in any file - just because a file has an extension of .txt doesn't mean it's definitely a text file. It could have content which is actually MP3-encoded audio data, for example. Whether the OS uses the file extension or the content to work out what to do with the file is up to the OS.

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