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package javax.servlet.jsp.tagext;

/**
 * Information on the scripting variables that are created/modified by
 * a tag (at run-time). This information is provided by TagExtraInfo
 * classes and it is used by the translation phase of JSP.
 *
 * <p>
 * Scripting variables generated by a custom action have an associated 
 * scope of either AT_BEGIN, NESTED, or AT_END.
 *
 * <p>
 * The class name (VariableInfo.getClassName) in the returned objects
 * is used to determine the types of the scripting variables.
 * Note that because scripting variables are assigned their values
 * from scoped attributes which cannot be of primitive types,
 * &quot;boxed&quot; types such as <code>java.lang.Integer</code> must 
 * be used instead of primitives.
 *
 * <p>
 * The class name may be a Fully Qualified Class Name, or a short
 * class name.
 *
 * <p>
 * If a Fully Qualified Class Name is provided, it should refer to a
 * class that should be in the CLASSPATH for the Web Application (see
 * Servlet 2.4 specification - essentially it is WEB-INF/lib and
 * WEB-INF/classes). Failure to be so will lead to a translation-time
 * error.
 *
 * <p>
 * If a short class name is given in the VariableInfo objects, then
 * the class name must be that of a public class in the context of the
 * import directives of the page where the custom action appears. 
 * The class must also be in the CLASSPATH for the Web Application 
 * (see Servlet 2.4 specification - essentially it is WEB-INF/lib and
 * WEB-INF/classes). Failure to be so will lead to a translation-time
 * error.
 *
 * <p><B>Usage Comments</B>
 * <p>
 * Frequently a fully qualified class name will refer to a class that
 * is known to the tag library and thus, delivered in the same JAR
 * file as the tag handlers. In most other remaining cases it will
 * refer to a class that is in the platform on which the JSP processor
 * is built (like Java EE). Using fully qualified class names in this
 * manner makes the usage relatively resistant to configuration
 * errors.
 *
 * <p>
 * A short name is usually generated by the tag library based on some
 * attributes passed through from the custom action user (the author),
 * and it is thus less robust: for instance a missing import directive
 * in the referring JSP page will lead to an invalid short name class
 * and a translation error.
 *
 * <p><B>Synchronization Protocol</B>
 *
 * <p>
 * The result of the invocation on getVariableInfo is an array of
 * VariableInfo objects.  Each such object describes a scripting
 * variable by providing its name, its type, whether the variable is
 * new or not, and what its scope is.  Scope is best described through
 * a picture:
 *
 * <p>
 * <IMG src="doc-files/VariableInfo-1.gif"
 *      alt="NESTED, AT_BEGIN and AT_END Variable Scopes"/>
 *
 *<p>
 * The JSP 2.0 specification defines the interpretation of 3 values:
 * 
 * <ul>
 * <li> NESTED, if the scripting variable is available between
 * the start tag and the end tag of the action that defines it.
 * <li>
 * AT_BEGIN, if the scripting variable is available from the start tag
 * of the action that defines it until the end of the scope.
 * <li> AT_END, if the scripting variable is available after the end tag
 * of the action that defines it until the end of the scope.
 * </ul>
 *
 * The scope value for a variable implies what methods may affect its
 * value and thus where synchronization is needed as illustrated by
 * the table below.  <b>Note:</b> the synchronization of the variable(s)
 * will occur <em>after</em> the respective method has been called.
 *
 * <blockquote>
 * <table cellpadding="2" cellspacing="2" border="0" width="55%"
 *        bgcolor="#999999" summary="Variable Synchronization Points">
 *   <tr align="center">
 *     <td valign="top" colspan="6" bgcolor="#999999"><u><b>Variable Synchronization
 *     Points</b></u><br>
 *     </td>
 *   </tr>
 *   <tr>
 *     <th valign="top" bgcolor="#c0c0c0">&nbsp;</th>
 *     <th valign="top" bgcolor="#c0c0c0" align="center">doStartTag()</th>
 *     <th valign="top" bgcolor="#c0c0c0" align="center">doInitBody()</th>
 *     <th valign="top" bgcolor="#c0c0c0" align="center">doAfterBody()</th>
 *     <th valign="top" bgcolor="#c0c0c0" align="center">doEndTag()</th>
 *     <th valign="top" bgcolor="#c0c0c0" align="center">doTag()</th>
 *   </tr>
 *   <tr>
 *     <td valign="top" bgcolor="#c0c0c0"><b>Tag<br>
 *     </b></td>
 *     <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff"><br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff"><br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, AT_END<br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff"><br>
 *     </td>
 *   </tr>
 *   <tr>
 *     <td valign="top" bgcolor="#c0c0c0"><b>IterationTag<br>
 *     </b></td>
 *     <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff"><br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, AT_END<br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff"><br>
 *     </td>
 *   </tr>
 *   <tr>
 *     <td valign="top" bgcolor="#c0c0c0"><b>BodyTag<br>
 *     </b></td>
 *     <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<sup>1</sup><br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<sup>1</sup><br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, AT_END<br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff"><br>
 *     </td>
 *   </tr>
 *   <tr>
 *     <td valign="top" bgcolor="#c0c0c0"><b>SimpleTag<br>
 *     </b></td>
 *     <td valign="top" align="center" bgcolor="#ffffff"><br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff"><br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff"><br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff"><br>
 *     </td>
 *     <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, AT_END<br>
 *     </td>
 *   </tr>
 * </table>
 * <sup>1</sup> Called after <code>doStartTag()</code> if 
 * <code>EVAL_BODY_INCLUDE</code> is returned, or after 
 * <code>doInitBody()</code> otherwise.
 * </blockquote>
 *
 * <p><B>Variable Information in the TLD</B>
 * <p>
 * Scripting variable information can also be encoded directly for most cases
 * into the Tag Library Descriptor using the &lt;variable&gt; subelement of the
 * &lt;tag&gt; element.  See the JSP specification.
 */

public class VariableInfo {

    /**
     * Scope information that scripting variable is visible only within the
     * start/end tags.
     */
    public static final int NESTED = 0;

    /**
     * Scope information that scripting variable is visible after start tag.
     */
    public static final int AT_BEGIN = 1;

    /**
     * Scope information that scripting variable is visible after end tag.
     */
    public static final int AT_END = 2;


    /**
     * Constructor
     * These objects can be created (at translation time) by the TagExtraInfo
     * instances.
     *
     * @param varName The name of the scripting variable
     * @param className The type of this variable
     * @param declare If true, it is a new variable (in some languages this will
     *     require a declaration)
     * @param scope Indication on the lexical scope of the variable
     */

    public VariableInfo(String varName,
			String className,
			boolean declare,
			int scope) {
	this.varName = varName;
	this.className = className;
	this.declare = declare;
	this.scope = scope;
    }

    // Accessor methods
    
    /**
     * Returns the name of the scripting variable.
     *
     * @return the name of the scripting variable
     */
    public String getVarName() { 
        return varName; 
    }
    
    /**
     * Returns the type of this variable.
     *
     * @return the type of this variable
     */
    public String getClassName() { 
        return className; 
    }
    
    /**
     * Returns whether this is a new variable.
     * If so, in some languages this will require a declaration.
     *
     * @return whether this is a new variable.
     */
    public boolean getDeclare() { 
        return declare; 
    }
    
    /**
     * Returns the lexical scope of the variable.
     * 
     * @return the lexical scope of the variable, either AT_BEGIN, AT_END,
     *    or NESTED.
     * @see #AT_BEGIN
     * @see #AT_END
     * @see #NESTED
     */
    public int getScope() { 
        return scope; 
    }


    // == private data
    private String varName;
    private String className;
    private boolean declare;
    private int scope;
}

