CODEWITHSUNDEEP
javagenericshashmap
Julio Ramirez
Julio Ramirez

Reputation: 25

Why is Map<String, int> list = new HashMap<String, int> not permissible?

So as you can see be title I am confused on: 

Map<String, int> list = new HashMap<String, int>

I am a bit lost in class on this specific topic and would appreciate if anybody could explain why and how it actually works.

Upvotes: 1

Views: 3621

Answers (2)

Nirbhay Mishra
Nirbhay Mishra

Reputation: 1648

IN java Some thing like following happens

public interface Map<K, V> {
    public K getKey();            
    public V getValue();          
}

public class HashMap<K, V> implements Map<K, V> {

    private K key;              //1
    private V value;            //2

    public K getKey()   { return key; }
    public V getValue() { return value; }
 //other getter setter methods 

}

As In Here in place of<K,V> in

<String,int> int is a primitive type And we can't make object of primitive type. see //1 and //2 above in code

But <String,Integer> is possible as they are wrapper type and Objects can be made of them

Upvotes: 1

rgettman
rgettman

Reputation: 178333

The type int is not a class, it's a primitive type. Generic type parameters must be assigned classes, not primitive types. You can use

Map<String, Integer> list = new HashMap<String, Integer>();

instead. All Java primitive types have class wrappers, and as of Java 1.5, autoboxing allows expressions such as map.put("dummy", 1);, where 1 is autoboxed as an Integer.

Incidentally, it can be confusing to call a Map list. You could remove the confusion by calling it map.

Upvotes: 11

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