DefaultMapBuilder.java

/**
 *
 */
package net.objectlab.kit.collections;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import net.objectlab.kit.util.Pair;

/**
 * Inspired by the Google Collection builder.
 *
 * @author Benoit Xhenseval
 *
 */
public class DefaultMapBuilder<K, V> implements MapBuilder<K, V> {
    private final List<Pair<K, V>> entries = new ArrayList<>();
    private final String id;

    public DefaultMapBuilder(final String id) {
        this.id = id;
    }

    @Override
    public String getId() {
        return id;
    }

    /**
     * Associates {@code key} with {@code value} in the built map.
     */
    @Override
    public DefaultMapBuilder<K, V> put(final K key, final V value) {
        entries.add(new Pair<>(key, value));
        return this;
    }

    /**
     * Associates all of the given map's keys and values in the built map.
     *
     * @throws NullPointerException if any key or value in {@code map} is null
     */
    @Override
    public DefaultMapBuilder<K, V> putAll(final Map<? extends K, ? extends V> map) {
        for (final Entry<? extends K, ? extends V> entry : map.entrySet()) {
            put(entry.getKey(), entry.getValue());
        }
        return this;
    }

    /**
     * Returns a newly-created immutable map.
     *
     * @throws IllegalArgumentException if duplicate keys were added
     * @return
     */
    public Map<K, V> build() {
        return fromEntryList(entries);
    }

    private static <K, V> Map<K, V> fromEntryList(final List<Pair<K, V>> entries) {
        final int size = entries.size();
        if (size == 0) {
            return new HashMap<>();
        }
        final Map<K, V> m = new HashMap<>();
        for (final Pair<K, V> entry : entries) {
            m.put(entry.getElement1(), entry.getElement2());
        }
        return m;
    }
}