Java Generics Bounded Wildcard for List collection

import java.util.LinkedList;
import java.util.List;

public class Main {
   public static void main(String... args) {
      // Wildcard bounded parameterized types
      ////from  ww  w  . j a  v a2s. co  m
      List<? extends Number> cList;
      cList = new LinkedList<Number>();
      cList = new LinkedList<Integer>();
      cList = new LinkedList<Double>();

      // we can get(), but we can't add() with "? extends"
      cList.add(new Integer(5)); // add() not allowed; cList could be LinkedList<Double>
      Number cNum = cList.get(0);

      List<? super Integer> dList;
      dList = new LinkedList<Integer>();
      dList = new LinkedList<Number>();
      dList = new LinkedList<Object>();

      // we can do limited add()'s, but we can't get() with "? super"
      Integer dInt = dList.get(0); // get() not allowed; dList.get(0) could be a Number or Object
      dList.add(new Integer(5)); // OK
      Number dNum = new Double(7);
      dList.add(dNum); // won't compile; dList could be LinkedList<Integer>

   }
}