builder for HashMap

Question

Guava provides us with great factory methods for Java types, such as Maps.newHashMap().

But are there also builders for java Maps?

HashM         


        

Answer 1

Here's one I wrote

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.function.Supplier;

public class MapBuilder {

    private final Map map;

    /**
     * Create a HashMap builder
     */
    public MapBuilder() {
        map = new HashMap<>();
    }

    /**
     * Create a HashMap builder
     * @param initialCapacity
     */
    public MapBuilder(int initialCapacity) {
        map = new HashMap<>(initialCapacity);
    }

    /**
     * Create a Map builder
     * @param mapFactory
     */
    public MapBuilder(Supplier> mapFactory) {
        map = mapFactory.get();
    }

    public MapBuilder put(K key, V value) {
        map.put(key, value);
        return this;
    }

    public Map build() {
        return map;
    }

    /**
     * Returns an unmodifiable Map. Strictly speaking, the Map is not immutable because any code with a reference to
     * the builder could mutate it.
     *
     * @return
     */
    public Map buildUnmodifiable() {
        return Collections.unmodifiableMap(map);
    }
}

You use it like this:

Map map = new MapBuilder(LinkedHashMap::new)
    .put("event_type", newEvent.getType())
    .put("app_package_name", newEvent.getPackageName())
    .put("activity", newEvent.getActivity())
    .build();