具有通用类型变量List的类

Question

I'm reading about generic types. I'm able to understand that generic types can be used to specify the type of content can be consumed by objects or collections to avoid runtime error and solve it while compile time only.

I want to know how can I create a generic class whose type variable(T = List) is List. For example in below example its String.

import java.util.ArrayList;
import java.util.List;

public class Test<T> {

    T string;

    public Test(T in) {

        this.string = in;

    }

    public static void main(String args[]) {

        Test<String> o = new Test<String>("Generic");


    }
}

Answer 1

I want to know how can I create a generic class whose type variable(T = List) is List.

Specify the List as parameterized type.

To have a generic Test of List<String> do for example :

List<String> myList = new ArrayList<>();
...
Test<List<String>> o = new Test<>(myList);

Answer 2

If you want your list strictly to be a list of strings. Then simply declare your list as List<String>

Answer 3

in this way obliges the developer to use a class that belongs to the Collection es (List, ArrayList, Vector, ...)

public class Test<T extends Collection>{ ... }

UPDATE

public class Test<E,T extends Collection<E>>{ ... }

Answer 4

Just déclare your T like an extends of List Change this:

public class Test<T> {

to this

public class Test<T extends List> {

In this case, you will not be able to write this:

Test<String> o = new Test<String>();