title: why there are .dll or .py files
body: <p>I always have a question in my mind. When I look at the installation folder of a program, though the software is claimed to be written in Java, there are some dll / py or exe files in it.  This is completely weird to me as I used to believe a Java program should only contain .class files or jars. Can someone explain to me what is the reason behind this kind of setting? </p>
  
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  <p>I have read some tutorials about java native interface and is this the reason why there are dll and exe files?</p>