Adding String,ArrayList, etc objects to List

Question

I have a data structure Map < String, Map < ConfigKey, ConfigValue<Object > > >. This is like a Map of "namespace" to Map of "key" to "value". My parser reads config file and dynamically decides if the value should be treated as String or ArrayList.

I see error adding ArrayList to above data structure. Please show me how to fix this.

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

"I am facing trouble" is not a good error description. Please amend. — Maarten Bodewes, Jul 11 '15 at 22:33

score 3 · Answer 1 · edited May 23 '17 at 11:43

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

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

This would fix it

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

or

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

And please avoid raw-types in your code.

1 Answers1