将String，ArrayList等对象添加到列表中<Object>

Question

我有一个数据结构Map < String, Map < ConfigKey, ConfigValue<Object > > >。这就像是一个Map的“名字空间”到Map的“键”到“值”。我的解析器读取配置文件并动态决定是否将该值视为String或ArrayList。

我看到错误添加ArrayList以上的数据结构。请告诉我如何解决这个问题。

private Map<String, Map<ConfigKey, ConfigValue<Object>>> configuration = new HashMap<String, Map<ConfigKey, ConfigValue<Object>>>(); 
: 
configuration.get(groupName).put(new ConfigKey(key), new ConfigValue<Object>(override, value)); // works 
: 
configuration.get(groupName).put(new ConfigKey(key), new ConfigValue<List>(override, Arrays.asList(values))); // does not work 

Answer 1

ConfigValue<List> is not a ConfigValue<Object>. 

Read more about covariance and contravariance in Java或programming in general.

这将修复它

private Map<String, Map<ConfigKey, ConfigValue<? extends Object>>> configuration = new HashMap<String, Map<ConfigKey, ConfigValue<? extends Object>>>(); 

或

Map<String, Map<ConfigKey, ConfigValue<?>>> 

请避免raw-types在你的c颂。