SortMapByKeys.java

package com.levelup.java.collections;

import static org.hamcrest.collection.IsIterableContainingInOrder.contains;
import static org.junit.Assert.assertThat;

import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.TreeMap;
import java.util.stream.Collectors;

import org.apache.log4j.Logger;
import org.junit.Before;
import org.junit.Test;

import com.google.common.collect.Ordering;

/**
 * This example will demonstrate sorting a map by keys in java. For calories
 * burned it will assume you were 200 pounds and performed the activity for 30
 * minutes. The conversion was provided by
 * http://www.myfitnesspal.com/exercise/lookup.
 * 
 * @author Justin Musgrove
 * @see <a href=
 *      'http://www.leveluplunch.com/java/examples/sort-order-map-by-key/'>Sort
 *      map by key</a>
 * 
 */
public class SortMapByKeys {

	private static final Logger logger = Logger.getLogger(SortMapByKeys.class);

	Map<Integer, String> CALORIES_BURNED;

	@Before
	public void setUp() {

		CALORIES_BURNED = new HashMap<Integer, String>();
		CALORIES_BURNED.put(295, "Race walking");
		CALORIES_BURNED.put(249, "Punching bag");
		CALORIES_BURNED.put(499, "Rock climbing, ascending rock");
		CALORIES_BURNED.put(726, "Running (jogging), 10 mph (6 min mile)");
		CALORIES_BURNED.put(281, "Shoveling snow");
	}

	@Test
	public void sort_map_by_key_java() {

		TreeMap<Integer, String> caloriesBurnedSorted = new TreeMap<Integer, String>(
				CALORIES_BURNED);

		logger.info(caloriesBurnedSorted);

		assertThat(caloriesBurnedSorted.keySet(),
				contains(249, 281, 295, 499, 726));
	}

	@Test
	public void sort_map_by_key_java_reverse() {

		TreeMap<Integer, String> caloriesBurnedReverse = new TreeMap<Integer, String>(
				Collections.reverseOrder());

		caloriesBurnedReverse.putAll(CALORIES_BURNED);

		logger.info(caloriesBurnedReverse);

		assertThat(caloriesBurnedReverse.keySet(),
				contains(726, 499, 295, 281, 249));
	}

	@Test
	public void sort_map_by_key_java8() {

		Map<Integer, String> sortedMapByKey = CALORIES_BURNED
				.entrySet()
				.stream()
				.sorted(Map.Entry.comparingByKey())
				.peek(System.out::println)
				.collect(
						Collectors.toMap(Map.Entry::getKey,
								Map.Entry::getValue, (v1, v2) -> v1, // BinaryOperator
																		// merge
																		// function
								LinkedHashMap::new));

		assertThat(sortedMapByKey.keySet(), contains(249, 281, 295, 499, 726));
	}

	@Test
	public void sort_map_by_key_guava() {

		TreeMap<Integer, String> caloriesBurnedReverse = new TreeMap<Integer, String>(
				Ordering.natural().reverse());

		caloriesBurnedReverse.putAll(CALORIES_BURNED);

		logger.info(caloriesBurnedReverse);

		assertThat(caloriesBurnedReverse.keySet(),
				contains(726, 499, 295, 281, 249));
	}

}