Convert "Object" to "HashMap" in Java

Here is a example:

import java.util.HashMap;

class Main {
    public static void main(String[] args) {
        HashMap<Integer, Integer> a = new HashMap<Integer, Integer>();
        a.put(1,2);
        a.put(2,5);
        Object b = a;
        // Do something here to make the variable "b" become a HashMap
    }
}

I tried this

HashMap<Integer, Integer> c = (HashMap<Integer, Integer>) b;

I get this warning:

Unchecked cast: ‘java.lang.Object’ to ‘java.util.HashMap<java.lang.Integer,java.lang.Integer>’

>Solution :

The warning is expectable in this situation, because such a casting considered as an unsafe operation. From your example it is hard to say why do you need such a cast, maybe you should re-think your code to avoid it. But if there is no other option, you may leave it, because in runtime it will work. You may also consider to suppress the warning for the method or class:

@SuppressWarnings({"unchecked"})
public static void main(String[] args) {
   // your code there
}