Issue linking two classes together

Question

I'm running into a problem with my JSON2Apex code where I'm unable to define objects of another class in the current class I'm working on and I'm not sure where I'm running afoul. I tried changing the 'public class' to a 'global with sharing class ... extends ...' as referenced here, but I'm now getting the below error message:

Line: 1, Column: 27 Dependent class is invalid and needs recompilation: Class restCallout : Non-virtual and non-abstract type cannot be extended: JSON2Apex

I'm not sure how to tie one class (ie make one an ancestor class) into another so I can perform the following call:

JSON2Apex data = (JSON2Apex)JSON.deserialize(res.getBody(), JSON2Apex.class);

I've also tried making my JSON2Apex class a 'public virtual class' so I can 'extend' my "restCallout" class, however that yields a different error message as well:

Line: x, Column: 1 System.JSONException: Expected JSON2Apex.Value but found [line: x, column: x]

Class 1:

public class restCallout extends JSON2Apex{  
    public static void restGroups() { 
    HTTPRequest req = new HttpRequest();
    req.setMethod('GET');
    req.setHeader('Accept', 'application/json');
    req.setEndpoint('callout:rest_endpoint1/');
    HTTPResponse res = new Http().send(req);
    JSON2Apex data = (JSON2Apex)JSON.deserialize(res.getBody(), JSON2Apex.class);
    }
...
}

Class 2:

public virtual class JSON2Apex {
   public class...{
   }
}

Answer 1

Generally composition makes more sense than inheritance: build one class by incorporating other classes.

In your example, leave the generated JSON2Apex class unchanged (or better rename it to reflect the service it calls) and then just reference it in your class:

public class restCallout {  
    public static void restGroups() { 
        HTTPRequest req = new HttpRequest();
        req.setMethod('GET');
        req.setHeader('Accept', 'application/json');
        req.setEndpoint('callout:rest_endpoint1/');
        HTTPResponse res = new Http().send(req);
        JSON2Apex data = (JSON2Apex)JSON.deserialize(res.getBody(), JSON2Apex.class);
        ...
    }
}