How can I initialise a static Map?

Question

How would you initialise a static Map in Java?

Method one: static initialiser
Method two: instance initialiser (anonymous subclass) or some other m

Answer 1

public class Test {
    private static final Map myMap;
    static {
        Map aMap = ....;
        aMap.put(1, "one");
        aMap.put(2, "two");
        myMap = Collections.unmodifiableMap(aMap);
    }
}

If we declare more than one constant then that code will be written in static block and that is hard to maintain in future. So it is better to use anonymous class.

public class Test {

    public static final Map numbers = Collections.unmodifiableMap(new HashMap(2, 1.0f){
        {
            put(1, "one");
            put(2, "two");
        }
    });
}

And it is suggested to used unmodifiableMap for constants other wise it can't be treated as constant.