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'>
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    * Hashes the hashcode of the specified object into this object.
039    * 
040    * @param o The object whose hashcode will be hashed with this object.
041    * @return This object (for method chaining).
042    */
043   public HashCode add(Object o) {
044      o = unswap(o);
045      add(o == null ? 1 : o.hashCode());
046      return this;
047   }
048
049   /**
050    * Hashes the hashcode into this object.
051    * 
052    * <p>
053    * The formula is simply <code>hashCode = 31*hashCode + i;</code>
054    * 
055    * @param i The hashcode to hash into this object's hashcode.
056    * @return This object (for method chaining).
057    */
058   public HashCode add(int i) {
059      hashCode = 31*hashCode + i;
060      return this;
061   }
062
063   /**
064    * Return the calculated hashcode value.
065    * 
066    * @return The calculated hashcode.
067    */
068   public int get() {
069      return hashCode;
070   }
071
072   /**
073    * Converts the object to a normalized form before grabbing it's hashcode.
074    * 
075    * <p>
076    * Subclasses can override this method to provide specialized handling (e.g. converting numbers to strings so that
077    * <code>123</code> and <js>"123"</js> end up creating the same hashcode.)
078    * 
079    * <p>
080    * Default implementation does nothing.
081    * 
082    * @param o The object to normalize before getting it's hashcode.
083    * @return The normalized object.
084    */
085   protected Object unswap(Object o) {
086      return o;
087   }
088}