adding multiple entries to a HashMap at once in one statement

Question

I need to initialize a constant HashMap and would like to do it in one line statement. Avoiding sth like this:

  hashMap.put(\"One\", new Integer(1)); // add         


        

Answer 1

You can use the Double Brace Initialization as shown below:

Map hashMap = new HashMap()
{{
     put("One", 1);
     put("Two", 2);
     put("Three", 3);
}};

As a piece of warning, please refer to the thread Efficiency of Java “Double Brace Initialization" for the performance implications that it might have.