how to create a object of abstract class without implementing method

Question

In my Graph class i extends a abstract class List(That extends comparable). I want to make object of list but don't want to implement (abstract)method in graph class.Whoever extends Graph must implement that method. How i can do this?

graph

public abstract class Graph<T> extends List<T>{

private  List<List<T>> adjacencyList;
private  int vertexNumber;
private boolean directed;


public Graph(int vertex,boolean directed)
{
    vertexNumber=vertex;
    this.directed=directed;
    adjacencyList= new List<List<T>>()// The problem is here compiler wants the implementation of the abstract method.
    createVertex(vertexNumber);

}

Possible duplicate of [Abstract class in Java](http://stackoverflow.com/questions/1320745/abstract-class-in-java) — Raedwald, May 10 '16 at 17:36
You can't extend List because List is not a generic, and cannot be parameterized.; — FredK, May 10 '16 at 17:38
@FredK You **can** extend List , List **is** generic and **can** be parameterized. — cyroxis, May 10 '16 at 17:41

score 0 · Answer 1 · answered May 10 '16 at 17:34

0

you are defining an abstract class extending a List so basically you have no more than 2 options;

either implement the methods of the list
or defined abstract to and the class that inherits the Graph will have to handle it...

answered May 10 '16 at 17:34

ΦXocę 웃 Пepeúpa ツ

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cyroxis · Answer 2 · 2016-05-10T17:40:41.323

You can not create an instance of an abstract class, you must implement all methods.

However in your situation you just need to provide one of the existing implementations. Most likely an ArrayList

adjacencyList = new ArrayList<List<T>>();

If you look at the List there are several implementing classes listed.

Most common are: - ArrayList - LinkedList - Stack

Design Question: Why does your Graph extend List and then have a List of Lists? Typically you only do one of the following

Extend List, in this case your Graph is a list
List field, in this case your Graph has a list

It is confusing to have both relationships on one object.

FredK · Accepted Answer · 2016-05-10T18:29:50.133

0

You could do this to force subclasses to provide a means to create the list:

public abstract class Graph<T> {
   private List<List<T>> x;

   public Graph(int vertex,boolean directed) {
      adjacencyList = createListOfList();
   }

   protected abstract List<List<T>> createListOfList();
}

edited May 10 '16 at 18:29

answered May 10 '16 at 17:46

FredK

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score 0 · Answer 4 · answered May 10 '16 at 18:01

since you have provide PRIVATE access modifier in :

private  List<List<T>> adjacencyList;
private  int vertexNumber;
private boolean directed;

so, even if you another class (suppose) A extends Graph, it would be able to access those variables. Try with public access specifier, it may help.

THANK YOU

how to create a object of abstract class without implementing method

4 Answers4