HashCodeUtil


1   // Copyright (c) 2003-2007, Jodd Team (jodd.sf.net). All Rights Reserved.
2   
3   package jodd.util;
4   
5   /**
6    * Collected methods which allow easy implementation of <code>hashCode()</code>.
7    * Based on items 7 and 8 from "Effective Java" book.
8    * <p>
9    * Usage scenarion:<br>
10   * <pre>
11   * int result = HashCodeUtil.SEED;
12   * result = HashCodeUtil.hash(result, fIsDecrepit);
13   * ...
14   * </pre>
15   *
16   * todo: Add primitive arrays.
17   */
18  public class HashCodeUtil {
19  
20      /**
21       * An initial hash code value to which is added contributions from fields.
22       * Using a non-zero value decreases collisons of hash code values.
23       */
24      public static final int SEED = 173;
25  
26      public static final int PRIME = 37;
27  
28      /**
29       * Calculate hash code for booleans.
30       */
31      public static int hash(int seed, boolean aBoolean) {
32          return (PRIME * seed) + (aBoolean ? 1 : 0);
33      }
34  
35      /**
36       * Calculate hash code for chars.
37       */
38      public static int hash(int seed, char aChar) {
39          return (PRIME * seed) + (int) aChar;
40      }
41  
42      /**
43       * Calculate hash code for ints.
44       */
45      public static int hash(int seed, int aInt) {
46          return (PRIME * seed) + aInt;
47      }
48  
49      /**
50       * Calculate hash code for longs.
51       */
52      public static int hash(int seed, long aLong) {
53          return (PRIME * seed) + (int) (aLong ^ (aLong >>> 32));
54      }
55  
56      /**
57       * Calculate hash code for floats.
58       */
59      public static int hash(int seed, float aFloat) {
60          return hash(seed, Float.floatToIntBits(aFloat));
61      }
62  
63      /**
64       * Calculate hash code for doubles.
65       */
66      public static int hash(int seed, double aDouble) {
67          return hash(seed, Double.doubleToLongBits(aDouble));
68      }
69  
70      /**
71       * Calculate hash code for Objects. Object is a possibly-null object field, and possibly an array.
72       * <p>
73       * If <code>aObject</code> is an array, then each element may be a primitive
74       * or a possibly-null object.
75       */
76      public static int hash(int seed, Object   aObject) {
77          int result = seed;
78          if (aObject == null) {
79              result = hash(result, 0);
80          } else if (aObject.getClass().isArray() == false) {
81              result = hash(result, aObject.hashCode());
82          } else {
83              Object  [] objects = (Object  []) aObject;
84              int length = objects.length;
85              for (int idx = 0; idx < length; ++idx) {
86                  result = hash(result, objects[idx]);
87              }
88          }
89          return result;
90      }
91  
92  }
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