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A set of utilities and tools to speed up and ease programming in Java.
There is a newer version: 0.5
/*
 * (c) 2005 David B. Bracewell
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package com.davidbracewell.collection;

import com.davidbracewell.conversion.Cast;
import com.google.common.collect.Lists;
import com.google.common.primitives.Doubles;

import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

/**
 * Methods for comparing and sorting.
 *
 * @author David B. Bracewell
 */
public final class Sorting {

  private Sorting() {
  }

  @SuppressWarnings("unchecked")
  public static int compare(Object o1, Object o2) {
    if (o1 == o2) {
      return 0;
    } else if (o1 == null) {
      return -1;
    } else if (o2 == null) {
      return 1;
    }
    return Cast.as(o1).compareTo(o2);
  }

  /**
   * Creates a comparator by examining an item. If the item is of type Comparable (i.e. is not null and implements the
   * Comparable interface), a comparator is returned that uses the Comparable method. Otherwise a hashcode based
   * comparator is returned.
   *
   * @param   The type of the comparator
   * @param item An example item to help and determine the best comparator
   * @return A Comparator
   */
  public static  Comparator comparator(T item) {
    if ((item != null && item instanceof Comparable)) {
      return Sorting::compare;
    }
    return Sorting.hashCodeComparator();
  }

  /**
   * Compares two objects based on their hashcode.
   *
   * @param  the type of object being compared
   * @return A simplistic comparator that compares hash code values
   */
  public static  Comparator hashCodeComparator() {
    return (o1, o2) -> {
      if (o1 == o2) {
        return 0;
      } else if (o1 == null) {
        return -1;
      } else if (o2 == null) {
        return 1;
      }
      return Doubles.compare(o1.hashCode(), o2.hashCode());
    };
  }

  /**
   * Sorts a Map by value.
   *
   * @param        the type parameter
   * @param        the type parameter
   * @param map       The map to sort
   * @param ascending True if in ascending (natural) order, False if in descending order
   * @return A List of Entry containing the map entries in sorted order.
   */
  public static > List> sortMapEntriesByValue(final Map map,
                                                                                     final boolean ascending) {
    return sortMapEntries(map, new MapEntryComparator(false, ascending));
  }

  /**
   * Sorts a Map using a given Comparator
   *
   * @param         the type parameter
   * @param         the type parameter
   * @param map        The map to sort
   * @param comparator The compartor to use for sorting the map entries
   * @return A List of Entry containing the map entries in sorted order.
   */
  public static  List> sortMapEntries(final Map map,
                                                        final Comparator> comparator) {
    List> rval = Lists.newArrayList(map.entrySet());
    Collections.sort(rval, comparator);
    return rval;
  }

  /**
   * Creates a comparator for Map entries. Requires that the element being sorted on implements
   * Comparable.
   *
   * @param        the Key type
   * @param        the value type
   * @param sortByKey True sort by key, False sort by value
   * @param ascending True sort in ascending order, False in descending order
   * @return A comparator for sorting map entries.
   */
  public static  Comparator> mapEntryComparator(boolean sortByKey, boolean ascending) {
    return new MapEntryComparator<>(sortByKey, ascending);
  }

  static class MapEntryComparator implements Comparator> {

    private final boolean ascending;
    private final boolean sortByKey;

    private MapEntryComparator(boolean sortByKey, boolean ascending) {
      this.sortByKey = sortByKey;
      this.ascending = ascending;
    }

    @Override
    public int compare(Entry o1, Entry o2) {
      if (sortByKey) {
        return (ascending ? 1 : -1) * Cast.>as(o1.getKey()).compareTo(o2.getKey());
      } else {
        return (ascending ? 1 : -1) * Cast.>as(o1.getValue()).compareTo(o2.getValue());
      }
    }
  }//END OF MapEntryComparator

}// END OF Sorting