Adding String,ArrayList, etc objects to List<Object>

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
– Maarten Bodewes, Commented Jul 11, 2015 at 22:33

Community · Accepted Answer · 2017-05-23 11:43:59Z

3

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.

edited May 23, 2017 at 11:43

CommunityBot

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answered Jul 11, 2015 at 21:53

Sleiman Jneidi

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