Exploring wildcard types, or the so called question mark type, in Java.

Viewer.java

package wild;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Viewer {
	
	public void process1(List<Object> items) {
		for (Object i : items)
			i.toString();
	}
	
	public void process2(List<Item> items) {
		for (Item i : items)
			i.process();
	}
	
	public void process3(List<?> items) {
	    for (Object i : items) 
			i.toString();
	}

	public void process4(List<? extends Item> items) {
		for (Item i : items)
			i.process();
	}
}