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

Not quite a builder, but using an initializer:

Map<String, String> map = new HashMap<String, String>() {{
    put("a", "1");
    put("b", "2");
}};

Answer 2

Here is a very simple one ...

public class FluentHashMap<K, V> extends java.util.HashMap<K, V> {
  public FluentHashMap<K, V> with(K key, V value) {
    put(key, value);
    return this;
  }

  public static <K, V> FluentHashMap<K, V> map(K key, V value) {
    return new FluentHashMap<K, V>().with(key, value);
  }
}

then

import static FluentHashMap.map;

HashMap<String, Integer> m = map("a", 1).with("b", 2);

See https://gist.github.com/culmat/a3bcc646fa4401641ac6eb01f3719065

Answer 3

Underscore-java can build hashmap.

Map<String, Object> value = U.objectBuilder()
        .add("firstName", "John")
        .add("lastName", "Smith")
        .add("age", 25)
        .add("address", U.arrayBuilder()
            .add(U.objectBuilder()
                .add("streetAddress", "21 2nd Street")
                .add("city", "New York")
                .add("state", "NY")
                .add("postalCode", "10021")))
        .add("phoneNumber", U.arrayBuilder()
            .add(U.objectBuilder()
                .add("type", "home")
                .add("number", "212 555-1234"))
            .add(U.objectBuilder()
                .add("type", "fax")
                .add("number", "646 555-4567")))
        .build();
    // {firstName=John, lastName=Smith, age=25, address=[{streetAddress=21 2nd Street,
    // city=New York, state=NY, postalCode=10021}], phoneNumber=[{type=home, number=212 555-1234},
    // {type=fax, number=646 555-4567}]}