Is it possible to add a value to a collection in Java AutoValue?

Question

I have a Java AutoValue class with a List attribute. I'd like to allow the builder to append to the List rather than having to pass the entire constructed list.

Example:

import com.google.auto.value.AutoValue;
@AutoValue
public abstract class Deck {
    public abstract List<Card> cards();
    public static Builder builder() {
        return new AutoValue_Card.Builder()
            .cards(new ArrayList<Card>());
    }
    @AutoValue.Builder
    public abstract static class Builder {
        public abstract Builder cards(List<Card> cards);
        /**
         * Append card to cards in the constructed Deck.
         */
        public Builder addCard(Card card) {
            // Is it possible to write this function?
        }
    }
}

What's the best solution for writing the addCard function? Does AutoValue somehow support this already? The intermediate cards property in the constructed class not visible to the Builder so I can't access it directly. I could try to bypass the Builder directly by keeping my own copy of cards in the Builder, is that the only option here?

Answer 1

In case someone finds it useful - here is the actual code of what I assume Kevin suggested. It was not obvious when I first stumbled upon his reply, so here you go:

import com.google.auto.value.AutoValue;
import com.google.common.collect.ImmutableList;

@AutoValue
public abstract class Hand {
  public static Builder builder() {
    return new AutoValue_Hand.Builder();
  }

  public abstract Builder toBuilder();

  public abstract String name();

  public abstract ImmutableList<String> cards();

  @AutoValue.Builder
  public static abstract class Builder {

    public abstract Builder name(String name);

    protected abstract ImmutableList.Builder<String> cardsBuilder();

    public Builder addCard(String card) {
      cardsBuilder().add(card);
      return this;
    }

    public abstract Hand build();
  }
}

Usage:

Hand fullHouseHand = Hand.builder()
    .name("Full House")
    .addCard("King")
    .addCard("King")
    .addCard("King")
    .addCard("10")
    .addCard("10")
    .build();
System.out.print(fullHouseHand);

Output:

Hand{name=Full House, cards=[King, King, King, 10, 10]}