ImmutableMap.Builder from a HashMap

Question

I have a HashMap<K,V> of defaults values per keys.

I want to convert it to an ImmutableMap.Builder As I have another ImmutableMap which I want to merge and override into the original HashMap. I want to override some of the default pairs and eventually build a ImmutableMap.

How can I convert the HashMap to ImmutableMap.Builder?

I haven't seen ImmutableMap.Builder constructor that gets a HashMap.

Answer 1

Simply use putAll or am I missing something here? You cannot modify existing keys while building, but you can add more:

    Map<String, String> srcMap = Map.of("A", "a", "B", "b", "C", "c");

    ImmutableMap<String, String> map = ImmutableMap.<String, String> builder()
            .putAll(srcMap)
            .put("D", "d")
            .build();

    map.forEach((k,v) -> System.out.printf ("[%s:%s]", k, v));

You could modify the srcMap itself before you invoke putAll if you want to override the existing values.

Also, if you have a HashMap that is ready to be converted to an ImmutableMap, you can skip the builder part and just use copyOf:

ImmutableMap<String, String> finalMap = ImmutableMap.copyOf(srcMap);