Sort a map by the natural order of its keys. - Java java.util

Java examples for java.util:Map Key

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Description

Sort a map by the natural order of its keys.

Demo Code

/**/*from  w  ww .  ja  va2 s  .  c om*/
 * Copyright 2009-2016 Three Crickets LLC.
 * <p>
 * The contents of this file are subject to the terms of the LGPL version 3.0:
 * http://www.gnu.org/copyleft/lesser.html
 * <p>
 * Alternatively, you can obtain a royalty free commercial license with less
 * limitations, transferable or non-transferable, directly from Three Crickets
 * at http://threecrickets.com/
 */
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.logging.Logger;

public class Main{
    /**
     * Sort a map by the natural order of its keys.
     * 
     * @param <K>
     *        The map key class
     * @param <V>
     *        The map value class
     * @param map
     *        The map
     * @return The sorted map
     */
    public static <K extends Comparable<? super K>, V> LinkedHashMap<K, V> sortedMap(
            Map<K, V> map) {
        LinkedList<Map.Entry<K, V>> list = new LinkedList<Map.Entry<K, V>>(
                map.entrySet());
        Collections.sort(list, new Comparator<Map.Entry<K, V>>() {
            public int compare(Map.Entry<K, V> o1, Map.Entry<K, V> o2) {
                try {
                    return (o1.getKey()).compareTo(o2.getKey());
                } catch (ClassCastException x) {
                    // Because Java generics are erased, we could get a wrong
                    // key type
                    Map.Entry<?, ?> oo1 = o1;
                    Map.Entry<?, ?> oo2 = o2;
                    Logger.getLogger(
                            CollectionUtil.class.getCanonicalName())
                            .warning(
                                    "Can't compare "
                                            + oo1.getKey().getClass() + "("
                                            + oo1.getKey() + ") and "
                                            + oo2.getKey().getClass() + "("
                                            + oo2.getKey() + ")");
                    return (oo1.getKey().toString()).compareTo(oo2.getKey()
                            .toString());
                }
            }
        });

        LinkedHashMap<K, V> result = new LinkedHashMap<K, V>();
        for (Map.Entry<K, V> entry : list)
            result.put(entry.getKey(), entry.getValue());
        return result;
    }
}

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