Java tutorial
//package com.java2s; import java.util.Collections; import java.util.List; import java.util.Map; public class Main { public static <K, V> List<V> getValueList(Map<K, List<V>> map, K key) { List<V> valueList = map.get(key); if (valueList == null) { return Collections.emptyList(); } return valueList; } }