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Java Tutorial: Generics in java | Java Generics [The extends wildcard boundary]

A.java

public class A
{
    private int value = 10;

    public int getValue()
    {
        return value;
    }

    public void setValue(int value)
    {
        this.value = value;
    }

}

public class B extends A
{

}

public class C extends A
{

}

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

public class GenericDemo
{

    public static void main(String[] args)
    {
        GenericDemo genericDemo = new GenericDemo();

        List<A> listA = new ArrayList<A>();
        listA.add(new A());
        genericDemo.processElements(listA);

        List<B> listB = new ArrayList<B>();
        listB.add(new B());
        genericDemo.processElements(listB);

        List<C> listC = new ArrayList<C>();
        listC.add(new C());
        genericDemo.processElements(listC);
    }

    public void processElements(List<? extends A> list)
    {
        for (A a : list)
        {
            System.out.println(a.getClass());
            System.out.println("value =  "+a.getValue());
            System.out.println("------------");
        }
    }

}

class A
value =  10
------------
class B
value =  10
------------
class C
value =  10
------------