MapUtils.java Source code

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Here is the source code for MapUtils.java

Source

//package sk.hasto.java.collections;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

/**
 * Utility functions for working with Maps.
 * 
 * @author Branislav Hasto
 */
public final class MapUtils {

    /**
     * Sorts map by values in ascending order.
     * 
     * @param <K>
     *            map keys type
     * @param <V>
     *            map values type
     * @param map
     * @return
     */
    public static <K, V extends Comparable<V>> LinkedHashMap<K, V> sortMapByValue(Map<K, V> map) {
        List<Entry<K, V>> sortedEntries = sortEntriesByValue(map.entrySet());
        LinkedHashMap<K, V> sortedMap = new LinkedHashMap<K, V>(map.size());
        for (Entry<K, V> entry : sortedEntries) {
            sortedMap.put(entry.getKey(), entry.getValue());
        }

        return sortedMap;
    }

    /**
     * Sorts map entries by value in ascending order.
     * 
     * @param <K>
     *            map keys type
     * @param <V>
     *            map values type
     * @param entries
     * @return
     */
    private static <K, V extends Comparable<V>> List<Entry<K, V>> sortEntriesByValue(Set<Entry<K, V>> entries) {
        List<Entry<K, V>> sortedEntries = new ArrayList<Entry<K, V>>(entries);
        Collections.sort(sortedEntries, new ValueComparator<V>());
        return sortedEntries;
    }

    /**
     * Komparator podla hodnot v polozkach mapy.
     * 
     * @param <V>
     *            typ hodnot
     */
    private static class ValueComparator<V extends Comparable<V>> implements Comparator<Entry<?, V>> {
        public int compare(Entry<?, V> entry1, Entry<?, V> entry2) {
            return entry1.getValue().compareTo(entry2.getValue());
        }
    }

}