Meaning of? in Map
Method createBuilderFactory in Javax. Json Needs Argument of Type Map Generally, We Have Map with Like Map(Some Other Data Types in Place of String) but I...
Method createBuilderFactory in javax.json needs argument of type Map<String, ?>
Generally, we have map with like Map<String, String>(some other data types in place of String)
But I didn't understand what does ? stands for. And in order to pass argument of type Map<String, ?>, how I should define the map.
Can someone please help me to understand this better?
2 Answers
In Java generics the ? stands for wildcard, which represent any object.
If you create a method that takes Map<String, ?> you are saying that you expect a Map that maps from String keys to any possible object values:
public static void main(String[] args) {
Map<String, Object> map1 = null;
Map<String, String> map2 = null;
test(map1);
test(map2);
}
private static void test(Map<String, ?> settings) {}
I had difficulties when I need to pass Map<String, ?> to my function, which was accepting Map<String, Object>. And this cut it:
Map<String, ?> mapQuestion = ...
mapObject = (Map<String, Object>)mapQuestion;
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