What does the following Java code demonstrate?

import java.util.Collections;
import java.util.List;
import java.util.ArrayList;
public class Main {
    public static void main(String[] args) {
        List<String> items = new ArrayList<>();
        items.add("item1");
        items.add("item2");
        Collections.fill(items, "replaced");
        System.out.println(items.get(0));
    }
}