How does Karel run without “main” method?

Question

I was wondering in the program like Karel the Robot runs because it does not used main() method. Instead it used run() method:

import stanford.karel.Karel;

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Answer 1

There's nothing weird about it. The CollectNewspaperKarel class is just extending the behavior of Karel. It doesn't need to have a main method.

The class that will be the entry point of the program does need to have a main method and create an instance of CollectNewspaperKarel, like:

public class MyProgram {

    public static void main(String[] args) {
        CollectNewspaperKarel cnpk = new CollectNewspaperKarel();
        cnpk.run();
    }
}

Or the instance of CollectNewspaperKarel could be a static field:

public class MyProgram {
    private static CollectNewspaperKarel cnpk = new CollectNewspaperKarel();
    public static void main(String[] args) {
        cnpk.run();
    }
}

Karel is not an application, it's an API. You make the application.