ExactCompatibilityPolicy


1   /*
2    * ModuleLoader - A generic, policy-driven class loader.
3    * Copyright (c) 2004, Richard S. Hall
4    * All rights reserved.
5    *
6    * Redistribution and use in source and binary forms, with or without
7    * modification, are permitted provided that the following conditions
8    * are met:
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11   *     notice, this list of conditions and the following disclaimer.
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32   * Contact: Richard S. Hall (heavy@ungoverned.org)
33   * Contributor(s):
34   *
35  **/
36  package org.ungoverned.moduleloader.search.compatibility;
37  
38  import org.ungoverned.moduleloader.search.CompatibilityPolicy;
39  
40  /**
41   * This class implements a simple version numbering compatibility policy for the
42   * <tt>ImportSearchPolicy</tt> where only exact version numbers are considered
43   * to be compatible.  This policy simply returns the result of
44   * "<tt>leftId.equals(rightId) && leftVersion.equals(rightVersion)</tt>". Any
45   * calls to the <tt>compare()</tt> method result in an exception since this
46   * policy has no basis for comparing identifiers and versions.
47   * @see org.ungoverned.moduleloader.search.CompatibilityPolicy
48   * @see org.ungoverned.moduleloader.search.ImportSearchPolicy
49  **/
50  public class ExactCompatibilityPolicy implements CompatibilityPolicy
51  {
52      /**
53       * Compares two versioned identifiers, but since this policy has
54       * no understanding of how to compare identifiers, it always throws
55       * an <tt>IllegalArgumentException</tt>.
56       * @param leftId the identifier to test for compatibility.
57       * @param leftVersion the version number to test for compatibility.
58       * @param rightId the identifier used as the compatibility base line.
59       * @param rightVersion the version used as the compatibility base line.
60       * @return <tt>0</tt> if the identifiers are equal, <tt>-1</tt> if the
61       *         left identifier is less then the right identifier, and <tt>1</tt>
62       *         if the left identifier is greater than the right identifier.
63       * @throws java.lang.IllegalArgumentException if the two identifiers
64       *         are not comparable, i.e., they refer to completely different
65       *         entities.
66      **/
67      public int compare(
68          Object   leftId, Object   leftVersion,
69          Object   rightId, Object   rightVersion)
70      {
71          throw new IllegalArgumentException  ("Identifiers are not comparable.");
72      }
73  
74      /**
75       * Returns whether the first import/export target is compatible
76       * with the second. This method simply uses the "<tt>equals()</tt>" method
77       * to test both the identifier and the verison number.
78       * @param leftId the identifier to test for compatibility.
79       * @param leftVersion the version number to test for compatibility.
80       * @param rightId the identifier used as the compatibility base line.
81       * @param rightVersion the version used as the compatibility base line.
82       * @return <tt>true</tt> if the left version number object is compatible
83       *         with the right version number object, otherwise <tt>false</tt>.
84      **/
85      public boolean isCompatible(
86          Object   leftId, Object   leftVersion,
87          Object   rightId, Object   rightVersion)
88      {
89          return leftId.equals(rightId) && leftVersion.equals(rightVersion);
90      }
91  }
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