HashMap as a static member in java

Question

I want to pass the HashMap as a static member for each instance of the new class. However, every time I try to execute .get or.put in my HashMap, I get a NullPointerException. Help!

I do: public class EmailAccount { private static HashMap<String,Integer> name_list;and then name_list.put(last_name, occurences);Even name_list.containsKey(last_name);returns NullPointer.

This is related to an earlier question: Count string occurrences in Java

Answer 1

You need to create an instance.

private static Map<String, Integer> name_list = new HashMap<String, Integer>();

See also:

• Java Tutorial - Creating Objects
• Java Build Tutorial - Map Interface

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Answer 2

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private static HashMap<String, Integer> name_list = new HashMap<String, Integer>();

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Answer 3

You have not created an instance of the list. You declared this, but did not create an instance.

Answer 4

You created a field that may contain a HashMap, but you didn’t put anything into it

You need to put new HashMap<String, Integer>()in your box.