Java’s Inheritance Hierarchy with Cyclic Characteristics
If Java code contains a cyclic inheritance involving class A, a compiler error message will be displayed. This error message will also occur if class A inherits from class B and vice versa. It is important to note that cyclic inheritance hierarchies are not allowed in Java.
Cyclic inheritance hierarchy in Java
Although Java does not permit following cyclic inheritance hierarchy, it is not the prohibition that I’m concerned about. Rather, I’m curious about the precise cause of the compilation error that is thrown.
class A extends B<> class B extends C<> class C extends A<> // this will give you compile time error. At what point will the compiler generate an error when I type the following code? class C extends A<>
Creating such a connection is impossible as it establishes an endless recursive loop. To define class C , one requires class A , to define class A , class B is necessary, and to define class B , class C must be defined. This cycle continues indefinitely, leading to an illogical outcome, and the compiler is unable to handle it.
Consider the term «extends» in Java, where a child class effectively inherits all properties of its super class and also adds new and specific members to its own object.
Extension can be described as an order relation, where A extending B implies that A is greater than B (and not just greater than or equal to B). In the given case, if B is less than C, then it is clear that C cannot be less than A.
Apart from the logical issues discussed in other responses, there exists a practical problem that needs to be addressed.
During instantiation, it is necessary to initialize the classes in Java, with the superclass being initialized first. However, in the case of a cycle, the initialization code will ascend the inheritance hierarchy in an attempt to initialize the superclass, but it will never be reached.
It is imperative to prohibit this for Java.
By utilizing the IS-A relationship between C and B , we can simplify the problem to these statements.
class A extends C<> class C extends A<> The error is due to a conflict that the compiler has detected.
Java — Cyclic inheritance uses, I dug up this interesting reference: basically it says that cyclic inheritance is valid as long as there are no repeated fields, as the lookup for any field just needs to traverse one loop of the cycle to find out a meaning. If a field is repeated then none of the two definitions is more valid than the other and …
Inheritance in Java | #16 | Cyclic Inheritance (Not Allowed
JAVA & WEB | Session 9 | Inheritance :- https://goo.gl/6kQycjWatch the complete web series «Java & Web» on YouTube. It’s complete, comprehensive and …
Cyclic inheritance uses
In case I create the subsequent Java code:
The message given is both compiler error and inheritance involving in a cyclic manner.
If I create two classes, A and B, and A inherits B while B inherits A, the same outcome occurs.
I find it logical since it is difficult to conceive of how it could be achieved.
After inquiring about this, a professor from my university informed me that there are languages that facilitate this feature. He expressed disappointment that Java does not permit it and shared that he had worked on projects involving cyclic inheritance. However, I struggled to comprehend the technicalities of his explanation. He further revealed that he had faced issues where he wished to utilize cyclic inheritance.
Can you enlighten me on the potential applications of cyclic inheritance? Under what circumstances is it feasible and how can it be implemented? Are there any issues where this technique could prove advantageous?
I came across a fascinating source which suggests that cyclic inheritance is acceptable, provided that there are no duplicated fields. In this case, the search for a field requires traversing just one cycle to determine its significance. However, if a field is repeated, neither of the two definitions is prioritized, resulting in a potential issue.
Assume you wish to assign distinct features to a person as a human and a voter. Here’s an example of pseudo-code for achieving this.
class Person extends Human: String name; class Human extends Voter: String language; class Voter extends Person: Country residence; One can now refer to various attributes of a person without establishing a hierarchy. For instance, a person can be represented as a Person (with a name), a Human (who speaks a language), or a Voter (residing in a specific country). There is no aspect that holds more significance over the others.
Though it is fascinating, I find it impractical to implement beyond research projects. Envision a scenario where constructors for every class pass parameters to their respective super() constructors; the entire structure could be easily compromised with a mistake.
The provided pseudocode fails to compile in Java 8 and other languages, except for Cecil as indicated by the provided link. Despite the absence of any legitimate use cases, cyclic inheritance was disallowed. This does not necessarily imply that the idea is fundamentally unfeasible, merely that implementing the special circumstance is not worthwhile given the lack of practical applications.
If the classes were at the same level of hierarchy, it would be feasible. The class hierarchy can be visualized as a tree, which is how Java perceives it. Java requires the hierarchy to be at least one level above or more. In other programming languages, it is possible to inherit attributes from a class on the same level as the one being used.
I fail to comprehend the concept of cyclic inheritance and its usefulness as perceived by your professor. It should be noted that the IS-A relationship, which signifies that B is a subclass of A and can be used in place of A without any issues (as per the Liskov substitution principle), is the basis of this inheritance.
If A is a subclass of B and B is a subclass of A, then they must have identical external interfaces. This is due to the fact that adding a method to one class will automatically inherit it to the other, requiring either an override or the other implementation to be obtained.
You may encounter various situations where unusual side effects occur, particularly when utilizing method A.foo() that calls both super.foo() and B.foo() , which in turn call super.foo() . Allowing such behavior seems impractical.
The inheritance structure is designed to resemble a tree, with each subclass defining the characteristics of the classes above it. However, having two classes at the same level within the tree does not serve any meaningful purpose.
As an MSDTHOT with a designation of running Java , I beg to differ from the approved solution claiming the absence of errors in their code. To demonstrate this, I have written and compiled the following code:
class Person extends Human: String name; class Human extends Voter: String language; class Voter extends Person: String residence; Upon receiving an error message, it was reported that there is a cyclic inheritance involving the Person object.
In the Java programming language, cyclic inheritance is not allowed.
How to fix cyclic inheritance involving on android interface?, private class CreateOfferCommand implements Command part occur cyclic inheritance involving. and implement MainActivity.Command here must either be declared abstract or implement abstract method ‘execute (String, JSONObject)’ in ‘Command message. how to fix this problem? thanks. @update
Cyclic inheritance involving
My attempt is to incorporate a navigation drawer into my project with the help of fragments. The navigation drawer implemented is already integrated and is functioning properly. However, upon clicking on the fragments, an error message pops up stating: java.lang.RuntimeException: com.example.saarikakumar.factsappfull.MainActivity@1758ab2 must implement onfragmentinteractionlistener .
As I attempt to integrate the necessary methods into my fragment, an error message appears indicating a cyclic inheritance issue with the fragment. Below is the code for my fragment that caused this error.
import android.content.Context; import android.net.Uri; import android.os.Bundle; import android.support.v4.app.Fragment; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; /** * A simple subclass. * Activities that contain this fragment must implement the * interface * to handle interaction events. * Use the factory method to * create an instance of this fragment. */ public class FirstFragment extends Fragment implements FirstFragment.OnFragmentInteractionListener < // TODO: Rename parameter arguments, choose names that match // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER private static final String ARG_PARAM1 = "param1"; private static final String ARG_PARAM2 = "param2"; // TODO: Rename and change types of parameters private String mParam1; private String mParam2; private OnFragmentInteractionListener mListener; public FirstFragment() < // Required empty public constructor >/** * Use this factory method to create a new instance of * this fragment using the provided parameters. * * @param param1 Parameter 1. * @param param2 Parameter 2. * @return A new instance of fragment SecondFragment. */ // TODO: Rename and change types and number of parameters public static FirstFragment newInstance(String param1, String param2) < FirstFragment fragment = new FirstFragment(); Bundle args = new Bundle(); args.putString(ARG_PARAM1, param1); args.putString(ARG_PARAM2, param2); fragment.setArguments(args); return fragment; >@Override public void onCreate(Bundle savedInstanceState) < super.onCreate(savedInstanceState); if (getArguments() != null) < mParam1 = getArguments().getString(ARG_PARAM1); mParam2 = getArguments().getString(ARG_PARAM2); >> @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) < // Inflate the layout for this fragment return inflater.inflate(R.layout.fragment_first, container, false); >// TODO: Rename method, update argument and hook method into UI event public void onButtonPressed(Uri uri) < if (mListener != null) < mListener.onFragmentInteraction(uri); >> @Override public void onAttach(Context context) < super.onAttach(context); if (context instanceof OnFragmentInteractionListener) < mListener = (OnFragmentInteractionListener) context; >else < throw new RuntimeException(context.toString() + " must implement OnFragmentInteractionListener"); >> @Override public void onDetach() < super.onDetach(); mListener = null; >@Override public void onFragmentInteraction(Uri uri) < >/** * This interface must be implemented by activities that contain this * fragment to allow an interaction in this fragment to be communicated * to the activity and potentially other fragments contained in that * activity. *
* See the Android Training lesson Communicating with Other Fragments for more information. */ public interface OnFragmentInteractionListener < // TODO: Update argument type and name void onFragmentInteraction(Uri uri); >>
Despite its age, the error message clearly shows that the MainActivity at 1758ab2 needs to implement MSDT_A1.
The interface needs to be implemented by MainActivity in order for the fragment to access methods, as shown in mListener.notifyActivityOfSomething() .
Scala: Illegal Cyclic Inheritance on method, After taking some pointers on the magnet pattern and implicit resolution order here I have run into a strange problem pattern matching on my magnet classes. In the first example I get errors about illegal cyclic inheritance, but by switching the pattern matching I do not: sealed trait SeqOrFun [T1, T2] …
Things That Not All Programmers Know #1: Cyclic Inheritance
It has been a month since launching Significant Insignificance last October. Before anything I would like to thank everyone who cared enough to visit my blog and read what may seem to others nothing but insignificant thoughts. I hope you enjoyed reading it as much as I enjoyed writing it and promise more of the same.
Today, I decided to add a new series to my blog: “Things That Not All Programmers Know”. To make sure that I always write technical posts, on the first day of every month, I am going to post something (a trick, a tip, a best practice) related to programming that I believe not many young programmers know. This way, everyone- including me- gets to learn something new.
I am going to start this series with something relatively easy: Cyclic Inheritance. First, the definition:
“If a class or interface inherits from itself, even directly (i.e., it appears as its super-class or in its list of super-interfaces) or indirectly (i.e., one of its super-class or one of its super-interfaces inherits from it), a cyclic inheritance error is reported.”
Ok, this needs an example, consider the following code:
When trying to compile it, you get the error: “cyclic inheritance involving Person“.
This is cyclic inheritance; each class inherits the other: Employee is the subclass of Person, and Person is the subclass of Employee. This relationship is not possible.
Cyclic inheritance can be solved by determining the proper relationship; that is, finding out the right super class and the subclass. In the previous example, Person is the super class, so it should not try to inherit Employee and Employee is the subclass which will inherit Person. Correction is removing “extends Employee” from the Person class signature:
Hope this was useful. If you know any unique programming trick (Java or others) that you believe not many people know, do not hesitate to contact me. And again, for everyone who followed my blog throughout the previous month, thanks a lot for your dedication. This blog would not be alive if it weren’t for your support. Thank you.