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    <title>Generating Initial Values</title>
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      <h1>Generating Initial Values</h1>
      <p>
        <font size="-2">by&nbsp;Peter B. West</font>
      </p>
      <ul class="minitoc">
        <li>
          <a href="#N10014">Introduction</a>
        </li>
        <li>
          <a href="#N10021">
            Generating &amp; Accessing Initial Values
          </a>
          <ul class="minitoc">
            <li>
              <a href="#N10062">Properties without
                getInitialValue()</a>
            </li>
          </ul>
        </li>
      </ul>
      
      <a name="N10014"></a>
      <h3>Introduction</h3>
      <p>
        The <a href="simple-properties.html">previous section</a>
        discussed the common data elements in the simplest examples of
        property classes.  This section discusses more complex classes
        whose facilities are accessed only through various methods.
      </p>
      
      <a name="N10021"></a>
      <h3>
        Generating &amp; Accessing Initial Values
      </h3>
      <p>
        
        <a href= "javascript:window.top.displayCode( 'AutoRestore.html' )"
        ><span class="codefrag"
        >org.apache.fop.fo.properties.AutoRestore</span></a> is an
        example of the next most complex property class.  In
        addition to all of the common static fields, these classes
        have initial data value types which require the dynamic
        generation of a PropertyValue instance.
      </p>
      <p>
        The method <a href= "javascript:window.top.displayCode(
        'AutoRestore.html#getInitialValue' )" ><span
        class="codefrag">PropertyValue getInitialValue(int)</span></a>
        returns an instance of PropertyValue of the appropriate
        subclass containing the initial value for this property.  Like
        the static data fields, this value is, in turn, stored in the
        array of initial values maintained in the <a href=
        "javascript:window.top.displayCode(
        'PropertyConsts.html#PropertyConstsClass' )" ><span
        class="codefrag">PropertyConsts</span></a> singleton <a href=
        "javascript:window.top.displayCode( 'PropertyConsts.html#pconsts'
        )" ><span class="codefrag">pconsts</span></a>.` As with the
        fields, the first invocation of the method <a href=
        "javascript:window.top.displayCode(
        'PropertyConsts.html#setupProperty' )" ><span
        class="codefrag">setupProperty</span></a> on the property
        instantiates the singleton instance of the class, and stores
        that instance in the in the <a href=
        "javascript:window.top.displayCode(
        'PropertyConsts.html#properties' )" ><span
        class="codefrag">Property[] properties</span></a> array of <a
        href= "javascript:window.top.displayCode(
        'PropertyConsts.html#pconsts' )" ><span
        class="codefrag">pconsts</span></a>.
      </p>
      <p>
        Unlike the static data fields, however, the initial value is
        not immediately generated.  It is generated by a call to <a
        href= "javascript:window.top.displayCode(
        'PropertyConsts.html#getInitialValue' )" ><span
        class="codefrag">PropertyValue getInitialValue(int)</span></a>
        in <a href= "javascript:window.top.displayCode(
        'PropertyConsts.html#pconsts' )" ><span
        class="codefrag">pconsts</span></a>.  This call, in turn,
        locates the relevant instance of the particular property class
        in the <a href= "javascript:window.top.displayCode(
        'PropertyConsts.html#properties' )" ><span class= "codefrag"
        >properties</span> array of <span class= "codefrag"
        >PropertyConsts</span></a>, and invokes the <span class=
        "codefrag" >getInitialValue()</span> of that instance.  A
        side-effect of this call is to store the initial value in <a
        href= "javascript:window.top.displayCode(
        'PropertyConsts.html#initialValues' )" ><span
        class="codefrag">PropertyValue[] initialValues</span></a>.
      </p>
      <a name="N10062"></a>
      <h4>Properties without
        getInitialValue()</h4>
      <p>
        What about property classes which have no <span
        class="codefrag">getInitialValue()</span> method?  The
        simplest classes, e.g. <span
        class="codefrag">Character</span>, fall into this category.
        As <a href="classes-overview.html#property-classes">noted
        previously</a>, all of the property classes extend <span
        class="codefrag">org.apache.fop.fo.properties.Property</span>.
        <a href= "javascript:window.top.displayCode(
        'Property.html#PropertyClass' )" ><span
        class="codefrag">Property</span></a> provides a base <a href=
        "javascript:window.top.displayCode(
        'Property.html#getInitialValue' )" ><span
        class="codefrag">PropertyValue getInitialValue(int)</span></a>
        method to which the simple classes fall back.  Note that it is
        only valid for <span class="codefrag">NOTYPE_IT</span>, <span
        class="codefrag">AUTO_IT</span>, <span
        class="codefrag">NONE_IT</span> and <span
        class="codefrag">AURAL_IT</span> initial value types, so all
        classes which have any other initial value type must override
        this method.
      </p>

      <p>
        <strong>Previous:</strong> <a href = "simple-properties.html"
        >Simple property classes</a>
      </p>
      <p>
        <strong>Next:</strong> <a href= "enumerated-values.html"
                                  >Enumerated values</a>
      </p>
      
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