返回默认值而不是null的Java Map实现
我的代码中有一个 Map< String，List< String>> ，如果地图的，我会避免使用潜在的空指针#get（）方法返回一个空列表而不是null。 java API中有这样的东西吗？我应该只扩展 HashMap ？
I have a Map<String, List<String>> in my code, where I'd avoid potential null pointers if the map's #get() method returned an empty list instead of null. Is there anything like this in the java API? Should I just extend HashMap?
@ Jon的答案是好的直接做你要求的方式。
@Jon's answer is a good way to do what you are asking directly.
但是我觉得你可能想要实现的是一个多图;即从键到值集合的映射。如果是这种情况，那么你还应该查看Guava或Apache commons集合中的multimap类。
But is strikes me that what you might be trying to implement is a "multimap"; i.e. a mapping from a key to a collection of values. If that is the case, then you should also look at the multimap classes in Guava or Apache commons collections.
看看：
-
com.google.common.collect.Multimap界面及其实现，或 -
org.apache.commons.collections.MultiMap界面及其实现。 -
org.apache.commons.collections4.MultiMap界面及其实现（以前的MultiMap的新版本;在v4中引入） ）。
- the
com.google.common.collect.Multimapinterface and its implementations, or - the
org.apache.commons.collections.MultiMapinterface and its implementations. - the
org.apache.commons.collections4.MultiMapinterface and its implementations (a new version of the previous MultiMap; introduced in v4).