TwoDHashMap.java

package spiffy.core.util;

import java.util.HashMap;
import java.util.Set;

/**
 * A two-dimensional hashmap, is a HashMap that enables you to refer to values via two keys rather than one. The
 * underlying implementation is simply a HashMap containing HashMap, each of which maps to values.
 * <P>
 * This is quite useful e.g. when wanting to cache values such as "currency ration" based keys "day of year" and "year".
 * 
 * @see java.util.HashMap
 * @author Kasper B. Graversen
 */
public class TwoDHashMap<K1, K2, V> {
private HashMap<K1, HashMap<K2, V>> map = new HashMap<K1, HashMap<K2, V>>();

public TwoDHashMap() {

}

public TwoDHashMap(final HashMap<K1, HashMap<K2, V>> map) {
	this.map = map;
}

/**
 * Existence check of a value (or <tt>null</tt>) mapped to the keys.
 * 
 * @param firstKey
 *            first key
 * @param secondKey
 *            second key
 * @return true when an element (or <tt>null</tt>) has been stored with the keys
 */
public boolean containsKey(final K1 firstKey, final K2 secondKey) {
	// existence check on inner map
	final HashMap<K2, V> innerMap = map.get(firstKey);
	if( innerMap == null ) { return false; }
	return innerMap.containsKey(secondKey);
}

/**
 * Fetch a value from the Hashmap .
 * 
 * @param firstKey
 *            first key
 * @param secondKey
 *            second key
 * @return the element or null.
 */
public V get(final K1 firstKey, final K2 secondKey) {
	// existence check on inner map
	final HashMap<K2, V> innerMap = map.get(firstKey);
	if( innerMap == null ) { return null; }
	return innerMap.get(secondKey);
}

/**
 * Insert a value
 * 
 * @param firstKey
 *            first key
 * @param secondKey
 *            second key
 * @param value
 *            the value to be inserted. <tt>null</tt> may be inserted as well.
 * @return null or the value the insert is replacing.
 */
public Object set(final K1 firstKey, final K2 secondKey, final V value) {
	// existence check on inner map
	HashMap<K2, V> innerMap = map.get(firstKey);
	
	if( innerMap == null ) {
		// no inner map, create it
		innerMap = new HashMap<K2, V>();
		map.put(firstKey, innerMap);
	}
	
	return innerMap.put(secondKey, value);
}

/**
 * Returns the number of key-value mappings in this map for the first key.
 * 
 * @return Returns the number of key-value mappings in this map for the first key.
 */
public int size() {
	return map.size();
}

/**
 * Returns the number of key-value mappings in this map for the second key.
 * 
 * @return Returns the number of key-value mappings in this map for the second key.
 */
public int size(final K1 firstKey) {
	// existence check on inner map
	final HashMap<K2, V> innerMap = map.get(firstKey);
	if( innerMap == null ) { return 0; }
	return innerMap.size();
}

/**
 * Returns a set of the keys of the outermost map.
 */
public Set<K1> keySet() {
	return map.keySet();
}

}