Question

I am interested why this fragment of code produces a syntax error saying ImmutableMap cannot be resolved to a type:

ImmutableMap<String, String> advice = ImmutableMap<String, String>.builder()
                    .put(KEY1, VAL1)
                    .put(KEY2, VAL2)
                    .build();

While this code works as intended:

ImmutableMap<String, String> advice = ImmutableMap.<String, String>builder()
                    .put(KEY1, VAL1)
                    .put(KEY2, VAL2)
                    .build();

The period isn’t going where my mental model should and I was hoping someone could explain why the goes on the “method side” of the period. I’m using Guava’s ImmutableMap, but its not entirely relevant I don’t think. I think it has something to do with the generics but I’m not sure what and I’m not sure how to search to find a better answer since I don’t know what the concept would be called.

EDIT: For reference, ImmutableMap has this line for builder()

public static <K, V> Builder<K, V> builder() {
    return new Builder<K, V>();
}

Answer 1

builder() is a static method which has generic types associated with it, not the class it is defined in. It will be something like

public static <K,V> ImmutableMap.Builder<K,V> builder() { ... }

Note: the <K, V> here doesn’t have anything to do with the generic types of the class. (Which doesn’t have to be generic)