public class Poligon {

    public static void main(String argv[]) throws Exception {
        List<TestImpl> list = new ArrayList<>();
        list.add(new TestImpl());
        someMethod(list);
    }
    
    public static void someMethod(List<Test> list){
     
    }
}

public class TestImpl implements Test {

    @Override
    public String getName() {
        return "Denis";
    }

}

public interface Test {
    
    public String getName();
    
}

public static void someMethod(List list){
     Test t = (Test)list.get(0);
     // TODO
 }