001// ***************************************************************************************************************************
002// * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE file *
003// * distributed with this work for additional information regarding copyright ownership.  The ASF licenses this file        *
004// * to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance            *
005// * with the License.  You may obtain a copy of the License at                                                              *
006// *                                                                                                                         *
007// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
008// *                                                                                                                         *
009// * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an  *
010// * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the License for the        *
011// * specific language governing permissions and limitations under the License.                                              *
012// ***************************************************************************************************************************
013package org.apache.juneau.internal;
014
015/**
016 * Utility class for generating integer hash codes.
017 *
018 * <p>
019 * General usage:
020 * <p class='bcode w800'>
021 *    int hashCode = new HashCode().add("foobar").add(myobject).add(123).get();
022 * </p>
023 */
024public class HashCode {
025
026   private int hashCode = 1;
027
028   /**
029    * Create a new HashCode object.
030    *
031    * @return A new HashCode object.
032    */
033   public static final HashCode create() {
034      return new HashCode();
035   }
036
037   /**
038    * Calculates a hash code over the specified objects.
039    *
040    * @param objects The objects to calculate a hashcode over.
041    * @return A numerical hashcode value.
042    */
043   public static final int of(Object...objects) {
044      HashCode x = create();
045      for (Object oo : objects)
046         x.add(oo);
047      return x.get();
048   }
049
050   /**
051    * Hashes the hashcode of the specified object into this object.
052    *
053    * @param o The object whose hashcode will be hashed with this object.
054    * @return This object (for method chaining).
055    */
056   public HashCode add(Object o) {
057      o = unswap(o);
058      add(o == null ? 0 : o.hashCode());
059      return this;
060   }
061
062   /**
063    * Hashes the hashcode into this object.
064    *
065    * <p>
066    * The formula is simply <c>hashCode = 31*hashCode + i;</c>
067    *
068    * @param i The hashcode to hash into this object's hashcode.
069    * @return This object (for method chaining).
070    */
071   public HashCode add(int i) {
072      hashCode = 31*hashCode + i;
073      return this;
074   }
075
076   /**
077    * Return the calculated hashcode value.
078    *
079    * @return The calculated hashcode.
080    */
081   public int get() {
082      return hashCode;
083   }
084
085   /**
086    * Converts the object to a normalized form before grabbing it's hashcode.
087    *
088    * <p>
089    * Subclasses can override this method to provide specialized handling (e.g. converting numbers to strings so that
090    * <c>123</c> and <js>"123"</js> end up creating the same hashcode.)
091    *
092    * <p>
093    * Default implementation does nothing.
094    *
095    * @param o The object to normalize before getting it's hashcode.
096    * @return The normalized object.
097    */
098   protected Object unswap(Object o) {
099      return o;
100   }
101}