javac: file not found: polymorphism.music.Music.java or Error: Could not find or load main class pol

An example of what a java command should look like:

    java -Xmx100m com.acme.example.ListUsers fred joe bert

The above is going to cause the java command to do the following:

1. Search for the compiled version of the com.acme.example.ListUsers class.
2. Load the class.
3. Check that the class has a main method with signature, return type and modifiers given by public static void main(String[]). (Note, the method argument's name is NOT part of the signature.)
4. Call that method passing it the command line arguments ("fred", "joe", "bert") as a String[].

Q1. javac: file not found: polymorphism.music.Music.java 

A1: instead use

$ javac polymorphism/music/Music.java

also use absolute classpath, for example,

javac ~/user/polymorphism/music/Music.java

Q2: Error: Could not find or load main class polymorphism.music.Music

A1: be sure already has Music.class, then use

$ java polymorphism.music.Music

or 

java polymorphism/music/Music

If you want use javac/java in current directory, you need modify source code. Remove package sentences and some comments in exmaples code.

refereces:

1. https://stackoverflow.com/questions/18093928/what-does-could-not-find-or-load-main-class-mean