We have to be careful with abstract classes.

I get errors like this.

Class PlayApplication contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (Application:: registerRoutes in registerRoutes) in

This is the page for this error!

In this case, an abstract class called registerRoutes is created in the Application class.
It seems that when the Application class is taken over, this registerRoutes must be implemented.

Since abstract classes are designed to create subclasses in the first place, it is likely that an anomaly will occur if the contents of the abstract class are empty.

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I fixed the problem, but the above error persists... I thought I had created Application.php in a different folder!
I probably referred to that file. I've done it.