Interpreter looks for main method in an unexpected class

[Mike Grabl-j]

Examples are from "Thinking in Java".

import static net.mindview.util.Print.*;

class Art {
  Art() { print("Art constructor"); }
}
 
class Drawing extends Art {
  Drawing() { print("Drawing constructor"); }
}
 
public class Cartoon extends Drawing {
  public Cartoon() { print("Cartoon constructor"); }
  public static void main(String[] args) {
    Cartoon x = new Cartoon();
  }
}

Then I compile and run:

michael@michael:~/Downloads/thinking_in_java/TIJ4-code-master/examples/reusing$ javac -cp /home/michael/Downloads/thinking_in_java/TIJ4-code-master/examples Cartoon.java michael@michael:~/Downloads/thinking_in_java/TIJ4-code-master/examples/reusing$ java -cp /home/michael/Downloads/thinking_in_java/TIJ4-code-master/examples:. Cartoon.java error: can't find main(String[]) method in class: Art

The question is: Why is it looking for main class in the Art class? And how to make it run the main method in Cartoon class?

[Campbell Ritchie]

Don't writejavac ... XYZ.javafollowed byjava ... XYZ.javaIt is eitherjava ... XYZ.javaon its own without using javac at all (I think, Java11+ only), or it isjavac ... XYZ.java java ... XYZSince you appear to have compiled the class, you will have to use what it says in line 2 of the last code block.

[Mike Grabl-j]

Yes. The problem is solved. But the question is still here: why it looked for the main method in Art at all?

[Campbell Ritchie]

Mike Grabl-j wrote:Yes. . . .

Success

why it looked for the main method in Art at all?

Afraid I don't know. Please post some more details about your Java® installation, particularly what you get from these two instructions:-javac -version java -version...and maybe somebody else will have an idea.

[Junilu Lacar]

It's because when the command issued was java ... Cartoon.java, this caused Java to go into "source-file mode".

From the documentation (https://docs.oracle.com/en/java/javase/11/tools/java.html):

In source-file mode, the effect is as though the source file is compiled into memory, and the first class found in the source file is executed. Any arguments placed after the name of the source file in the original command line are passed to the compiled class when it is executed.

If the Cartoon class declaration had been at the top instead of at the bottom, it would have run fine. Of course, since you didn't know about source-file mode, then you would have been under the wrong impression that what you did was fine. If you moved the Drawing class to the top of the file and ran the same command, it would have complained about the Drawing class instead.

[Campbell Ritchie]

I am surprised it went into source file mode after a javac command. I thought you weren't allowed both types of execution instruction together.