Generics’ Bounded Wild Cards in Java PRO

When using a bounded wild card we can limit the parametric type as if we were saying that it can be any type as long as it extends or implements a specific type we specify.

package il.ac.hit.samples;

import java.util.Iterator;
import java.util.Vector;

public class BoundedWildCardSample
{
	public static double calculateTotal(Vector<? extends Shape> vicy)
	{
		double sum = 0;
		Iterator<? extends Shape> iterator = vicy.iterator();
		while (iterator.hasNext())
		{
			sum += iterator.next().area();
		}
		return sum;
	}

	public static void main(String args[])
	{
		double total = 0;
		Vector<Circle> victor = new Vector<Circle>();
		victor.add(new Circle(4));
		victor.add(new Circle(8));
		victor.add(new Circle(2));
		// victor.add(new Rectangle(4,2));
		// victor.add(new Rectangle(5,4));
		total = calculateTotal(victor);
		System.out.println("total=" + total);
	}
}

The following video clip shows how to use bounded wild cards and provides more in-depth explanation.