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