Question

I would like to create lock only once when map is initialized. Here is the code i am using.

public static Map<String, String> getOrderStatusInstance() {
    if (orderStatusMap == null) {
        synchronized (Utility.class) {
            orderStatusMap = new HashMap<String, String>();

            orderStatusMap.put("Key1", "Value1");
            orderStatusMap.put("Key2", "Value2");
            orderStatusMap.put("Key3", "Value3");
            orderStatusMap.put("Key4", "Value4");
        }
    }

    return orderStatusMap;
}

Answer 1

No, that’s a bad idea – you’re returning a mutable, non-thread-safe map. You’re also trying to implement double-checked locking, but not doing it properly – and it’s harder to get it right than it is to use static initialization.

I would create an immutable map (using Guava, for preference), ideally as part of class initialization:

private static final ImmutableMap<String, String> STATUS_MAP = ImmutableMap.of(
    "Key1", "Value1",
    "Key2", "Value2",
    "Key3", "Value3",
    "Key4", "Value4");

public static ImmutableMap<String, String> getOrderStatusInstance() {
    return STATUS_MAP;
}

(For more than 5 key/value pairs, use ImmutableMap.Builder.)

Do you really need it to be any lazier than that?