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Editorial Team
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Asked: 2026-05-27T18:59:08+00:00

public class arraylst { static HashMap<String,List<String>>hm; public static void main(String[] args) { hm.put(2,Arrays.asList(a,b,c)); }

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 public class arraylst
 {
   static HashMap<String,List<String>>hm;
   public static void main(String[] args)
   {
       hm.put("2",Arrays.asList("a","b","c"));
   }
 }

I don’t understand why this causes NullPointerException.

Can someone please help me out?

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1 Answer

  1. Editorial Team

    You need to set hm:

    hm = new HashMap<String, List<String>>();

    before you use it.

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