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1   package org.apache.torque.om;
2   
3   /*
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *   http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing,
15   * software distributed under the License is distributed on an
16   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17   * KIND, either express or implied.  See the License for the
18   * specific language governing permissions and limitations
19   * under the License.
20   */
21  
22  import java.io.Serializable;
23  import org.apache.torque.TorqueException;
24  
25  /***
26   * This class can be used to uniquely identify an object within
27   * an application.  There are four subclasses: StringKey, NumberKey,
28   * and DateKey, and ComboKey which is a Key made up of a combination
29   * ofthe first three.
30   *
31   * @author <a href="mailto:jmcnally@apache.org">John McNally</a>
32   * @version $Id: ObjectKey.java 473821 2006-11-11 22:37:25Z tv $
33   */
34  public abstract class ObjectKey implements Serializable, Comparable
35  {
36      /***
37       * The underlying key value.
38       */
39      protected Object key;
40  
41      /***
42       * Initializes the internal key value to <code>null</code>.
43       */
44      protected ObjectKey()
45      {
46          key = null;
47      }
48  
49      /***
50       * Returns the hashcode of the underlying value (key), if key is
51       * not null.  Otherwise calls Object.hashCode()
52       *
53       * @return an <code>int</code> value
54       */
55      public int hashCode()
56      {
57          if (key == null)
58          {
59              return super.hashCode();
60          }
61          return key.hashCode();
62      }
63  
64      /***
65       * Get the underlying object.
66       *
67       * @return the underlying object
68       */
69      public Object getValue()
70      {
71          return key;
72      }
73  
74      /***
75       * Appends a String representation of the key to a buffer.
76       *
77       * @param sb a <code>StringBuffer</code>
78       */
79      public void appendTo(StringBuffer sb)
80      {
81          sb.append(this.toString());
82      }
83  
84      /***
85       * Implements the compareTo method.
86       *
87       * @param obj the object to compare to this object
88       * @return a numeric comparison of the two values
89       */
90      public int compareTo(Object obj)
91      {
92          return toString().compareTo(obj.toString());
93      }
94  
95      /***
96       * Reset the underlying object using a String.
97       *
98       * @param s a <code>String</code> value
99       * @exception TorqueException if an error occurs
100      */
101     public abstract void setValue(String s) throws TorqueException;
102 }