please assist me with this challenge Exploring the Master Detail Template.

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class DummyContent {

    public static List<DummyItem> ITEMS = new ArrayList<DummyItem>();
    public static Map<String, DummyItem> ITEM_MAP = new HashMap<String, DummyItem>();

    static {
       addItem(new DummyItem("1", "The Avengers"));
addItem(new DummyItem("2", "The Hobbit"));
addItem(new DummyItem("3", "Ball of Fire"));




        addItem(new DummyItem("1", "Item 1"));
        addItem(new DummyItem("2", "Item 2"));
        addItem(new DummyItem("3", "Item 3"));
    }

    private static void addItem(DummyItem item) {
        ITEMS.add(item);
        ITEM_MAP.put(item.id, item);
    }

    /**
     * A dummy item representing a piece of content.
     */
    public static class DummyItem {
        public String id;
        public String content;

        public DummyItem(String id, String content) {
            this.id = id;
            this.content = content;
        }
    }
}