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| 3 | <head>
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| 4 | <meta http-equiv="Content-Language" content="en-us">
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| 5 | <title>Depend Task</title>
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| 6 | <link rel="stylesheet" type="text/css" href="../stylesheets/antmanual.css">
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| 7 | </head>
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| 8 |
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| 9 | <body>
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| 10 |
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| 11 | <h2>Depend</h2>
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| 12 |
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| 13 | A task to manage Java class file dependencies.
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| 14 |
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| 15 | <h3>Description</h3>
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| 16 |
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| 17 | <p>
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| 18 | The depend task works by determining which classes are out of date with
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| 19 | respect to their source and then removing the class files of any other
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| 20 | classes which depend on the out-of-date classes.
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| 21 | </p>
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| 22 |
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| 23 | <p> To determine the class dependencies, the depend task analyses the class
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| 24 | files of all class files passed to it. Depend does not parse your source code in
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| 25 | any way but relies upon the class references encoded into the class files by the
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| 26 | compiler. This is generally faster than parsing the Java source.</p>
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| 27 |
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| 28 | <p>
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| 29 | To learn more about how this information is obtained from the class files,
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| 30 | please refer to <a href="http://java.sun.com/docs/books/vmspec/">the Java
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| 31 | Virtual Machine Specification</a>
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| 32 | </p>
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| 33 |
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| 34 | <p> Since a class' dependencies only change when the class itself changes, the
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| 35 | depend task is able to cache dependency information. Only those class files
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| 36 | which have changed will have their dependency information re-analysed. Note that
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| 37 | if you change a class' dependencies by changing the source, it will be
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| 38 | recompiled anyway. You can examine the dependency files created to understand
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| 39 | the dependencies of your classes. Please do not rely, however, on the format of
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| 40 | the information, as it may change in a later release. </p>
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| 41 |
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| 42 | <p> Once depend discovers all of the class dependencies, it "inverts"
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| 43 | this relation to determine, for each class, which other classes are dependent
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| 44 | upon it. This "affects" list is used to discover which classes are
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| 45 | invalidated by the out of date class. The class files of the invalidated
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| 46 | classes are removed, triggering the compilation of the affected classes. </p>
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| 47 |
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| 48 | <p> The depend task supports an attribute, "closure" which controls
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| 49 | whether depend will only consider direct class-class relationships or whether it
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| 50 | will also consider transitive, indirect relationships. For example, say there
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| 51 | are three classes, A, which depends on B, which in-turn depend on C. Now say
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| 52 | that class C is out of date. Without closure, only class B would be removed by
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| 53 | depend. With closure set, class A would also be removed. Normally direct
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| 54 | relationships are sufficient - it is unusual for a class to depend on another
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| 55 | without having a direct relationship. With closure set, you will notice that
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| 56 | depend typically removes far more class files. </p>
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| 57 |
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| 58 | <p>The classpath attribute for <code><depend></code> is optional. If it is present,
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| 59 | depend will check class dependencies against classes and jars on this classpath.
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| 60 | Any classes which depend on an element from this classpath and which are older
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| 61 | than that element will be deleted. A typical example where you would use this
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| 62 | facility would be where you are building a utility jar and want to make sure
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| 63 | classes which are out of date with respect to this jar are rebuilt. You should
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| 64 | <b>not</b> include jars in this classpath which you do not expect to change,
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| 65 | such as the JDK runtime jar or third party jars, since doing so will just slow
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| 66 | down the dependency check. This means that if you do use a classpath for the
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| 67 | depend task it may be different from the classpath necessary to actually
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| 68 | compile your code.</p>
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| 69 |
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| 70 | <h3>Performance</h3>
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| 71 |
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| 72 | <p> The performance of the depend task is dependent on a
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| 73 | number of factors such as class relationship complexity and how many class files
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| 74 | are out of date. The decision about whether it is cheaper to just recompile all
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| 75 | classes or to use the depend task will depend on the size of your project and
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| 76 | how interrelated your classes are. </p>
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| 77 |
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| 78 |
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| 79 | <h3>Limitations</h3>
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| 80 |
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| 81 | <p> There are some source dependencies which depend will not detect. </p>
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| 82 |
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| 83 | <ul>
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| 84 | <li>If the Java compiler optimizes away a class relationship,
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| 85 | there can be a source dependency without a class dependency. </li>
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| 86 |
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| 87 | <li>Non public classes cause two problems. Firstly depend cannot relate
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| 88 | the class file to a source file. In the future this may be addressed
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| 89 | using the source file attribute in the classfile. Secondly, neither
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| 90 | depend nor the compiler tasks can detect when a non public class is
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| 91 | missing. Inner classes are handled by the depend task.</li>
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| 92 | </ul>
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| 93 |
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| 94 | The most obvious example of these limitations is that the task can't tell
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| 95 | which classes to recompile when a constant primitive data type exported
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| 96 | by other classes is changed. For example, a change in the definition of
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| 97 | something like
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| 98 | <pre>
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| 99 | public final class Constants {
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| 100 | public final static boolean DEBUG=false;
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| 101 | }
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| 102 | </pre> will not be picked up by other classes.
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| 103 |
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| 104 | <h3>Parameters</h3>
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| 105 | <table border="1" cellpadding="2" cellspacing="0">
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| 106 | <tr>
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| 107 | <td valign="top"><b>Attribute</b></td>
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| 108 | <td valign="top"><b>Description</b></td>
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| 109 | <td align="center" valign="top"><b>Required</b></td>
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| 110 | </tr>
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| 111 | <tr>
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| 112 | <td valign="top">srcDir</td>
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| 113 | <td valign="top">This is the directory where the source exists. depend
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| 114 | will examine this to determine which classes are out of date. If you use multiple
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| 115 | source directories you can pass this attribute a path of source directories.</td>
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| 116 | <td valign="top" align="center">Yes</td>
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| 117 | </tr>
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| 118 | <tr>
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| 119 | <td valign="top">destDir</td>
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| 120 | <td valign="top">This is the root directory of the class files which
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| 121 | will be analysed. If this is not present, the srcdir is used.</td>
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| 122 | <td valign="top" align="center">No</td>
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| 123 | </tr>
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| 124 | <tr>
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| 125 | <td valign="top">cache</td>
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| 126 | <td valign="top">This is a directory in which depend can store and
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| 127 | retrieve dependency information. If this is not present, depend will not
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| 128 | use a cache </td>
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| 129 | <td valign="top" align="center">No</td>
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| 130 | </tr>
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| 131 | <tr>
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| 132 | <td valign="top">closure</td>
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| 133 | <td valign="top">This attribute controls whether depend only removes
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| 134 | classes which directly depend on out of date classes. If this is set to true,
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| 135 | depend will traverse the class dependency graph deleting all affected
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| 136 | classes. Defaults to false</td>
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| 137 | <td valign="top" align="center">No</td>
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| 138 | </tr>
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| 139 | <tr>
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| 140 | <td valign="top">dump</td>
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| 141 | <td valign="top">If true the dependency information will be written to the debug level log
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| 142 | </td>
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| 143 | <td valign="top" align="center">No</td>
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| 144 | </tr>
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| 145 | <tr>
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| 146 | <td valign="top">classpath</td>
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| 147 | <td valign="top">The classpath containing jars and classes for which <code><depend></code> should also
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| 148 | check dependencies</td>
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| 149 | <td valign="top" align="center">No</td>
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| 150 | </tr>
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| 151 | </table>
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| 152 |
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| 153 | <h3>Parameters specified as nested elements</h3>
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| 154 | <p>The <code>depend</code> task's <code>classpath</code> attribute is a
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| 155 | <a href="../using.html#path">PATH-like structure</a> and can also be set
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| 156 | via a nested <code><classpath></code> element.</p>
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| 157 |
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| 158 | <p>Additionally,
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| 159 | this task forms an implicit
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| 160 | <a href="../CoreTypes/fileset.html">FileSet</a>
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| 161 | and supports all attributes of
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| 162 | <code><fileset></code> (<code>dir</code> becomes <code>srcdir</code>),
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| 163 | as well as the nested <code><include></code>,
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| 164 | <code><exclude></code>, and <code><patternset></code> elements.
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| 165 |
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| 166 | <h3>Examples</h3>
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| 167 | <pre><depend srcdir="${java.dir}"
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| 168 | destdir="${build.classes}"
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| 169 | cache="depcache"
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| 170 | closure="yes"/></pre>
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| 171 |
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| 172 | <p>removes any classes in the <code>${build.classes}</code> directory
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| 173 | that depend on out-of-date classes. Classes are considered out-of-date with
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| 174 | respect to the source in the <code>${java.dir}</code> directory, using the same
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| 175 | mechanism as the <code><javac></code> task. In this example, the
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| 176 | <code><depend></code> task caches its dependency
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| 177 | information in the <code>depcache</code> directory. </p>
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| 178 |
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| 179 | <pre>
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| 180 | <depend srcdir="${java.dir}" destdir="${build.classes}"
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| 181 | cache="depcache" closure="yes">
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| 182 | <include name="**/*.java"/>
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| 183 | <excludesfile name="${java.dir}/build_excludes"/>
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| 184 | </depend>
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| 185 | </pre>
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| 186 | <p>does the same as the previous example, but explicitly includes all
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| 187 | <code>.java</code> files, except those that match the list given
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| 188 | in <code>${java.dir}/build_excludes</code>.</p>
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| 189 |
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| 190 | <hr>
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| 191 | <p align="center">Copyright © 2001-2002,2004 The Apache Software Foundation.
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| 192 | All rights Reserved.</p>
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| 193 |
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| 194 | </body>
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| 195 | </html>
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| 196 |
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