HOW TO INITIALIZE A STATIC MAP?

Glen Martin

Total Post:27

Points:191
Posted by  Glen Martin
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How would you initialise a static Map in Java?

Method one: Static initializer 
Method two: instance initialiser (anonymous subclass) or some other method?

What are the pros and cons of each?

Here is an example illustrating two methods:
import java.util.HashMap;
import java.util.Map;
public class Test {
    private static final Map<Integer, String> myMap = new HashMap<Integer, String>();
    static {
        myMap.put(1, "one");
        myMap.put(2, "two");
    }
    private static final Map<Integer, String> myMap2 = new HashMap<Integer, String>(){
        {
            put(1, "one");
            put(2, "two");
        }
    };
}
  1. Mayank Tripathi

    Post:397

    Points:3117
    Re: How to Initialize a static Map?

    The instance initialiser is just syntactic sugar in this case, right? I don't see why you need an extra anonymous class just to initialize. And it won't work if the class being created is final.

    You can create an immutable map using a static initialiser too:
    public class Test {
        private static final Map<Integer, String> myMap;
        static {
            Map<Integer, String> aMap = ....;
            aMap.put(1, "one");
            aMap.put(2, "two");
            myMap = Collections.unmodifiableMap(aMap);
        }
    }

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