HashCode


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8     * under the terms of the GNU Lesser General Public License as
9     * published by the Free Software Foundation; either version 2.1 of
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14    * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15    * Lesser General Public License for more details.
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21    */
22  package org.jboss.util;
23  
24  import java.io.Serializable  ;
25  
26  /**
27   * A hash-code generator and a collection of static hash-code generation
28   * methods.
29   *
30   * @version <tt>$Revision: 1958 $</tt>
31   * @author  <a HREF="mailto:jason@planet57.com">Jason Dillon</a>
32   */
33  public final class HashCode
34     implements Serializable  , Cloneable  , Comparable  
35  {
36     /** Hashcode for a 'null' value. */
37     private static final int NULL_HASHCODE = 0;
38  
39     /** Hashcode for a 'true' boolean */
40     private static final int TRUE_HASHCODE = 1231; // completely arbitrary
41  
42     /** Hashcode for a 'false' boolean */
43     private static final int FALSE_HASHCODE = 1237; // completely arbitrary
44  
45     /** The hash-code value. */
46     private int value;
47  
48     /**
49      * Construct a new <tt>HashCode</tt> using the given <tt>int</tt> as the
50      * base value.
51      *
52      * @param value   <tt>int</tt> to use as the base value.
53      */
54     public HashCode(final int value) {
55        this.value = value;
56     }
57  
58     /**
59      * Construct a new <tt>HashCode</tt>.
60      */
61     public HashCode() {
62        this(0);
63     }
64  
65     /**
66      * Add the hash-code of the given value.
67      *
68      * @param b    Value to get hash-code from.
69      * @return     <i>This</i> <tt>HashCode</tt>.
70      */
71     public HashCode add(final boolean b) {
72        value ^= generate(b);
73        return this;
74     }
75  
76     /**
77      * Add the hash-code of the given value.
78      *
79      * @param n    Value to get hash-code from.
80      * @return     <i>This</i> <tt>HashCode</tt>.
81      */
82     public HashCode add(final byte n) {
83        value ^= n;
84        return this;
85     }
86  
87     /**
88      * Add the hash-code of the given value.
89      *
90      * @param n    Value to get hash-code from.
91      * @return     <i>This</i> <tt>HashCode</tt>.
92      */
93     public HashCode add(final char n) {
94        value ^= n;
95        return this;
96     }
97  
98     /**
99      * Add the hash-code of the given value.
100     *
101     * @param n    Value to get hash-code from.
102     * @return     <i>This</i> <tt>HashCode</tt>.
103     */
104    public HashCode add(final short n) {
105       value ^= n;
106       return this;
107    }
108 
109    /**
110     * Add the hash-code of the given value.
111     *
112     * @param n    Value to get hash-code from.
113     * @return     <i>This</i> <tt>HashCode</tt>.
114     */
115    public HashCode add(final int n) {
116       value ^= n;
117       return this;
118    }
119 
120    /**
121     * Add the hash-code of the given value.
122     *
123     * @param n    Value to get hash-code from.
124     * @return     <i>This</i> <tt>HashCode</tt>.
125     */
126    public HashCode add(final long n) {
127       value ^= generate(n);
128       return this;
129    }
130 
131    /**
132     * Add the hash-code of the given value.
133     *
134     * @param f    Value to get hash-code from.
135     * @return     <i>This</i> <tt>HashCode</tt>.
136     */
137    public HashCode add(final float f) {
138       value ^= generate(f);
139       return this;
140    }
141 
142    /**
143     * Add the hash-code of the given value.
144     *
145     * @param f    Value to get hash-code from.
146     * @return     <i>This</i> <tt>HashCode</tt>.
147     */
148    public HashCode add(final double f) {
149       value ^= generate(f);
150       return this;
151    }
152 
153    /**
154     * Add the hash-code of the given object.
155     *
156     * @param obj    Value to get hash-code from.
157     * @return        <i>This</i> <tt>HashCode</tt>.
158     */
159    public HashCode add(final Object   obj) {
160       value ^= generate(obj);
161       return this;
162    }
163 
164    /**
165     * Get the hash-code.
166     *
167     * @return   Hash-code.
168     */
169    public int hashCode() {
170       return (int)value;
171    }
172 
173    /**
174     * Compares this object with the specified <tt>int</tt> for order.
175     *
176     * @param other   Value to compare with.
177     * @return        A negative integer, zero, or a positive integer as
178     *                this object is less than, equal to, or greater than
179     *                the specified object.
180     */
181    public int compareTo(final int other) {
182       return (value < other) ? -1 : (value == other) ? 0 : 1;
183    }
184 
185    /**
186     * Compares this object with the specified object for order.
187     *
188     * @param other   Value to compare with.
189     * @return        A negative integer, zero, or a positive integer as
190     *                this object is less than, equal to, or greater than
191     *                the specified object.
192     *
193     * @throws ClassCastException    Object is not a <tt>HashCode</tt>.
194     */
195    public int compareTo(final Object   obj) throws ClassCastException   {
196       HashCode hashCode = (HashCode)obj;
197       return compareTo(hashCode.value);
198    }
199 
200    /**
201     * Test the equality of this <tt>HashCode</tt> and another object.
202     *
203     * @param obj    Object to test equality with.
204     * @return       True if object is equal.
205     */
206    public boolean equals(final Object   obj) {
207       if (obj == this) return true;
208 
209       if (obj != null && obj.getClass() == getClass()) {
210          return value == ((HashCode)obj).value;
211       }
212 
213       return false;
214    }
215 
216    /**
217     * Return a string representation of this <tt>HashCode</tt>.
218     *
219     * @return  A string representation of this <tt>HashCode</tt>.
220     */
221    public String   toString() {
222       return String.valueOf(value);
223    }
224 
225    /**
226     * Return a cloned copy of this <tt>HashCode</tt>.
227     *
228     * @return   Cloned <tt>HashCode</tt>.
229     */
230    public Object   clone() {
231       try {
232          return super.clone();
233       }
234       catch (CloneNotSupportedException   e) {
235          throw new InternalError  ();
236       }
237    }
238 
239    /////////////////////////////////////////////////////////////////////////
240    //                           Generation Methods                        //
241    /////////////////////////////////////////////////////////////////////////
242 
243    /**
244     * Generate a hash code for a boolean value.
245     *
246     * @param value   Boolean value to generate hash code from.
247     * @return        Hash code.
248     */
249    public static int generate(final boolean value) {
250       return value ? TRUE_HASHCODE : FALSE_HASHCODE;
251    }
252 
253    /**
254     * Generate a hash code for a long value.
255     *
256     * @param value   Long value to generate hash code from.
257     * @return        Hash code.
258     */
259    public static int generate(final long value) {
260       return (int)(value ^ (value >> 32));
261    }
262 
263    /**
264     * Generate a hash code for a double value.
265     *
266     * @param value   Double value to generate hash code from.
267     * @return        Hash code.
268     */
269    public static int generate(final double value) {
270       return generate(Double.doubleToLongBits(value));
271    }
272 
273    /**
274     * Generate a hash code for a float value.
275     *
276     * @param value   Float value to generate hash code from.
277     * @return        Hash code.
278     */
279    public static int generate(final float value) {
280       return Float.floatToIntBits(value);
281    }
282 
283    /**
284     * Generate a hash code for a byte array.
285     *
286     * @param bytes   An array of bytes to generate a hash code from.
287     * @return        Hash code.
288     */
289    public static int generate(final byte[] bytes) {
290       int hashcode = 0;
291 
292       for (int i=0; i<bytes.length; i++) {
293          hashcode <<= 1;
294          hashcode ^= bytes[i];
295       } 
296 
297       return hashcode;
298    }
299 
300    /**
301     * Generate a hash code for an object array.
302     *
303     * <p>Does not handle nested primitive array elements.
304     *
305     * @param array   Array to generate hashcode for.
306     * @param deep    True to traverse elements which are arrays to 
307     *                determine the elements hash code.
308     * @return        Hash code.
309     */
310    public static int generate(final Object   array[], final boolean deep) {
311       int hashcode = 0;
312 
313       for (int i=0; i<array.length; i++) {
314          if (deep && (array[i] instanceof Object  [])) {
315             hashcode ^= generate((Object  [])array[i], true);
316          }
317          else {
318             hashcode ^= array[i].hashCode();
319          }
320       } 
321 
322       return hashcode;
323    }
324 
325    /**
326     * Generate a shallow hash code for an object array.
327     *
328     * @param array   Array to generate hashcode for.
329     * @return        Hash code.
330     */
331    public static int generate(final Object   array[]) {
332       return generate(array, false);
333    }
334 
335    /**
336     * Generate a hash code for an object.
337     *
338     * @param obj     Object to generate hashcode for.
339     * @return        Hash code.
340     */
341    public static int generate(final Object   obj) {
342       if (obj != null) {
343          return obj.hashCode();
344       }
345 
346       return NULL_HASHCODE;
347    }
348 }
349
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