CODEWITHSUNDEEP
javagenericsinstance
Othman H
Othman H

Reputation: 75

Instantiating a generic class in a generic class

I have the following first generic class and its interface:

    public interface Generic1Interface<E extends Comparable> {
    ..
    }

    public class Generic1 <E extends Comparable> implements 
    Generic1Interface<E>  {
    .. //implementation of Doubly linked list using Node objects
    }

And the second generic class and its interface:

    public interface Generic2Interface<E extends Comparable> {
    ..
    }

    public class Generic2 <E extends Comparable> implements 
    Generic22Interface<E>  {
      Generic1Interface<E> list;
        //so nothing here but a reference to an object of type Generic1Interface<E>
    Generic2() {
      list = new Generic1();
    }

Suppose we're working on a method inside the second class, and we try to instantiate a new instance of the second class, and name it "result", then try to access its Generic2 instance, it will give an error:

    public Generic2Interface<E> union (E a, E b) {
      Generic2Interface<E> result = new Generic2();
      **result.list** = ....;

result.list will give an error: "list cannot be resolved or is not a field". I think there must be a workaround to instantiate a generic class in a generic class. Thanks.

EDIT: I need to conform to the interfaces in each implemented class. So as you can see the method union has to return object of type Generic2Interface that's why I declare result like this.

Upvotes: 1

Views: 106

Answers (1)

Vasan
Vasan

Reputation: 4956

You need a cast for result to Generic2 type. This works:

System.out.println(((Generic2)result).list);

Or this:

Generic2<E> result = new Generic2();
System.err.println(result.list);

Upvotes: 1

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