Inheritance using wild cards

Even though Integer is a sub class of Number, List<Integer> is not a sub class of List<Number>. Since List<Integer> and List<Number> are two different classes.

But Both the classes List<Number> and List<Integer> are the sub classes for List<?>.

Example 1
WildCardEx1.java

import java.util.*;

public class WildCardEx1{

    public static void main(String args[]){

        List<?> list1 = new ArrayList<Number>();

        List<?> list2 = new ArrayList<Integer>();

    }

}

 Similarly, List<Number>, List<Integer> are sub classes for List<? Extends Number>.

WildCardEx2.java

import java.util.*;

public class WildCardEx2{

    public static void main(String args[]){

        List<? extends Number> list1 = new ArrayList<Number>();

        List<? extends Number> list2 = new ArrayList<Integer>();

    }

}

 Similarly, List<Number>, List<Integer> are sub classes for List<? super Integer>.

WildCardEx3.java 

import java.util.*;

public class WildCardEx3 {

    public static void main(String args[]){

        List<? super Integer> list1 = new ArrayList<Number>();

        List<? super Integer> list2 = new ArrayList<Integer>();

    }

}

WildCardEx4.java  

import java.util.*;

public class WildCardEx4 {

    public static void main(String args[]){

       List<?> list1;

       List<? extends Number> list2;

       List<? extends Integer> list3;

       List<Integer> list4 = new ArrayList<Integer>();

       list1 = list2 = list3 = list4;

       List<Number> list5 = new ArrayList<Number>();

       list1 = list2 = list5;

    }

}

WildCardEx5.java 

import java.util.*;

public class WildCardEx5{

    public static void main(String args[]){

       List<?> list1;

       List<? super Integer> list2;

       List<? super Number> list3;

       List<Number> list4 = new ArrayList<Number>();

       list1 = list2 = list3 = list4;

       List<Integer> list5 = new ArrayList<Integer>();

       list1 = list2 = list5;

    }

}

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