import java.util.Iterator;
import java.util.LinkedHashMap;

public class HashMaps
{
	// There are three types of HashMaps:  HashMap, LinkedHashMap, TreeMap
	// Each HashMap entry contains a KEY and an associated VALUE

	// HashMap:        Does NOT maintain the order in which elements are initially entered
	// LinkedHashMap:  DOES maintain the order in which data is entered
	// TreeMap:        Allow the map elements to be sorted by their keys

	// HashMaps store data in "buckets", which contain key/value pairs; a single
	// bucket can hold multiple key/value pairs (often organized via a List)
	// Hashing refers to the process of retrieving the Value for a specific Key
	private static LinkedHashMap<Integer, String> mapData = new LinkedHashMap<Integer, String>();

	public static void main(String[] args)
	{
		// Inserting data into the HashMap
		mapData.put(37, "computer");
		mapData.put(22, "monitor");
		mapData.put(81, "keyboard");
		mapData.put(74, "mouse");
		mapData.put(6, "flash drive");

		// Retrieve/Display an individual HashMap Value; note that to find the Key
		// associated with a specific Value requires iterating through the HashMap
		System.out.println("Value associated with Key 22:  " + mapData.get(22));

		// Retrieve/Display all of the HashMap data
		ShowMapData();

		// Deleting data from the HashMap
		System.out.println("\nRemoving Values for Keys 81 and 37.");
		mapData.remove(81);
		mapData.remove(37);

		// Retrieve/Display all of the HashMap data
		ShowMapData();

		// Display HashMap data
		System.out.println("\nDoes HashMap contain KEY 74?  " + mapData.containsKey(74));
		System.out.println("Does HashMap contain VALUE 'monitor'?  " + mapData.containsValue("monitor"));

		System.out.println("\nSize of HashMap:  " + mapData.size());
		System.out.println("Is HashMap Empty?  " + mapData.isEmpty());

		// Change HashMap Data (could also use ".put")
		System.out.println("\nChanging the Value for Key 74.");
		mapData.replace(74, "speaker");
		ShowMapData();

		// Clear the HashMap
		System.out.println("\nClearing the HashMap.");
		mapData.clear();
		System.out.println("\nSize of HashMap:  " + mapData.size());
		System.out.println("Is HashMap Empty?  " + mapData.isEmpty());
	}

	public static void ShowMapData()
	{
		// Retrieve/Display all of the HashMap data
		System.out.println("\nComplete Map Data:");
		System.out.println("  All Keys:    " + mapData.keySet());
		System.out.println("  All Values:  " + mapData.values());

		System.out.println("\n  Via Iteration:");
		Iterator itr = mapData.keySet().iterator();
		while (itr.hasNext())
		{
			Integer key = (Integer)itr.next();
			System.out.println("    " + key + ":  " + mapData.get(key));
		}
	}
}