java File中File.exists() 与 File.isFile()区别?

/dev/null

File.isFile()

false

File.exists()

true

Use File.exists() when dealing with special files like named pipes, sockets or device files.

Those are not regular files nor directories nor symlinks so both File.isFile() and File.isDirectory() will return false while File.exists() will return true. For example /dev/null (on Unix compatible OSes) is a device file.

Theoretically there may be performance differences visible when processing large amounts of files. This depends also on filesystem, JVM implementation details, OS etc.

Eg. on Android File.exists() is implemented using access() system call while File.isFile()/File.isDirectory() use stat(). In this case processing stat() output requires more logic in userspace than access().