Java Generics example.

TestList.java

import java.util.*;

class A{ public int i; }
class B extends A { public int j; }

public class TestList{

    public static void main(String[] args){
        A a = new A(); a.i = 1;
        B b = new B(); b.i = 2; b.j = 3;

        List<A> alist = new LinkedList<A>();
        alist.add(a);
        alist.add(b);
        System.out.println("a.i: " + alist.get(0).i + "\n"
                           + "b.i: " + alist.get(1).i);
         // System.out.println("b.j: " + alist.get(1).j);
         // COMPILATION ERROR:
         // cannot find symbol
         // symbol  : variable j
        System.out.println("b.j: " + ((B)alist.get(1)).j);
    }
}