Java class and jar

What's the difference between java class (.class) and .jar ? Can I say .jar may contains serveral java classes ?

If there are serveral .class inside a .jar, how can I know which class to run first when I run the jar file ?

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Radek BaranowskiFull-stack Java DeveloperCommented:
Yes, there can be many classes in many packages in .jar file.

You specify which is the main class in the manifest:

Main class needs to contain main method (public static void main(String[] args) )

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Also just to clarify a .class file is compiled java code.  A .Jar is just a zipped archive file.  You can rename the extension to .zip and uncompress it with any zip tool.
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