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I would like to instantiate Map<String, List<String>> in Java,
I tried
Map<String, List<String>> foo = new <String, List<String>>();
and
Map<String, List<String>> foo = new <String, ArrayList<String>>();
None of them work. Does any one know how to instantiate this map in Java?
405
Let's create a map of string as key and int as value and initialize it with initializer_list i.e. }; std::initializer_list<std::pair<const std::string, int> > = { {"Riti",2}, {"Jack",4} }; std::initializer_list<std::pair<const std::string, int> > = { {"Riti",2}, {"Jack",4} };
The Static Initializer for a Static HashMap We can also initialize the map using the double-brace syntax: Map<String, String> doubleBraceMap = new HashMap<String, String>() {{ put("key1", "value1"); put("key2", "value2"); }};
toMap() method: This method includes creation of a list of the student objects, and uses Collectors. toMap() to convert it into a Map.
new HashMap<String, List<String>>();
or as gparyani commented:
new HashMap<>(); // type inference
Note: each entry needs to be given an instantiated List as a value. You cannot get("myKey").add("some_string_for_this_key"); the very first time you get() a List from it.
So, fetch a List, check if it's null.
If it's null, make a new list, add the string to it, put the List back. If it's anything but null, add to it, or do what you want.
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