Help.java

import java.util.Arrays;
import java.util.Collection;
import java.util.List;

public class Main {
    
    public interface Cat {
        
    }
    
    private static class Tortie implements Cat {
        
    }
    
    public static void main(String... args) {
        DoStuff<Cat> catDoStuff = new DoStuff<>();
        List<Tortie> torties = Arrays.asList(new Tortie());
        catDoStuff.go(torties); // sad
    }
    
    public static class DoStuff<T extends Cat> {
        
        void go(Collection<T> items) {
            
        }
    }
}