correct usage of generics while creating hashmap

Question

I have a hashMap where key is String and value could be Integer or long . Now in a method I am creating this HashMap and passing into other method something like

methodA(long a,Integer b)

{
Map<String,? super Number> hm = new HashMap<>();
hm.put("key1",a);
hm.put("key2",b);

invokeMethodC(hm);
}

invokeMethodC(Map<String, ?> uriVariables)
{
....
}

Just wanted to know whether i have used correct generics while creating hashMap object

Abhijeet Kushe · Accepted Answer · 2014-12-18 17:17:46Z

1

Don't use extends/super as you will not be able to put elements in a Map.It will give a compilation error

Map<String, Number> uriVariables = = new HashMap<>();

answered Dec 18, 2014 at 17:17

Abhijeet Kushe

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2 Comments

Programmer Over a year ago

I have used super not extends

Abhijeet Kushe Over a year ago

Yep just saw that .Corrected my answer.Have a look a this link for getting more info about adding elements with lower bounded wildcards docs.oracle.com/javase/tutorial/java/generics/lowerBounded.html

Evgeniy Dorofeev · Accepted Answer · 2014-12-18 17:55:08Z

1

Map<String,? super Number> will return Object on get(). It is better to use Map<String, Number> then put() will accept Long and Integer and get() will return Number

edited Dec 18, 2014 at 17:55

answered Dec 18, 2014 at 17:20

Evgeniy Dorofeev

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