How Can I create a generic HashMap to insert collections and objects?

Question

How Can I instantiate a HashMap to put collections and objects?.

//it's wrong
Map<String,?>params=new HashMap<String,? >
List<Person> lstperson=getPerson();
params.put("person",lstperson);
params.put("doc",objectDoc);
params.put("idSol",new Long(5));
service.method(params);

//method

public void method(Map<String, ?> params);

FWIW, this seems like a bad code smell: it looks like you ought to be storing this data in a class, not an untyped `Map`. — Louis Wasserman, Dec 18 '13 at 17:33

score 26 · Accepted Answer · answered Dec 18 '13 at 15:41

26

Declare the hash map as

Map<String,Object> params = new HashMap<String,Object>();

You can keep the declaration of

public void method(Map<String, ?> params);

as it is, as long as the method only every tries to read from the map.

answered Dec 18 '13 at 15:41

Dirk

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After creating a hashmap like this, how can I add an object of generic type to the hashmap? – birgersp Aug 21 '15 at 08:21

score 6 · Answer 2 · answered Dec 18 '13 at 15:42

6

All classes in Java extends Object. so you can use Object for a value type in a map, like

Map<String, Object> params = new HashMap<String, Object>

answered Dec 18 '13 at 15:42

bmanvelyan

149
4

score 5 · Answer 3 · answered Dec 18 '13 at 15:42

5

You need to change

Map<String,?>params=new HashMap<String,? >

to like this

Map<String,Object>params=new HashMap<String,Object>()

But its not good practice to put all type of objects into single map. Better you can create POJO and add it to map.

answered Dec 18 '13 at 15:42

Prabhakaran Ramaswamy

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It seems like the map itself should be a POJO instead. – Paul Bellora Dec 18 '13 at 15:58

score 0 · Answer 4 · answered Apr 11 '20 at 17:58

0

I cam here for substitute in Kotlin

You can declare in kotlin as :-

val map: Map<String, Any?>

answered Apr 11 '20 at 17:58

hitesh

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How Can I create a generic HashMap to insert collections and objects?

4 Answers4