Java Generics Lower Bounded Wildcards Example

A lower bounded wildcard is expressed using the wildcard character ('?'), following by the super keyword, followed by its lower bound: <? super A>.
GenericType<? super SubClass>

Lower Bounded Wildcards Example

import java.util.ArrayList;

import java.util.List;

/**
 * Wildcard Arguments With An Lower Bound Demo
 * @author javaguides.net
 *
 */

public class WildCardWithLoweroundExample {
 static void processElements(List<? super Integer> a) {
  for (Object element : a) {
   System.out.println(element);
  }
 }

 public static void main(String[] args) {
  // ArrayList Containing Integers

  List<Integer> a1 = new ArrayList<>();

  a1.add(10);

  a1.add(20);

  a1.add(30);

  processElements(a1);

  // ArrayList Containing Longs

  List<Long> a2 = new ArrayList<>();

  a2.add(100L);

  a2.add(200L);

  a2.add(300L);

  processElements(a2); // compiler error

 }
}
Output:
10
20
30

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