/*
 * ElementList.java July 2006
 *
 * Copyright (C) 2006, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 
 * implied. See the License for the specific language governing 
 * permissions and limitations under the License.
 */

package org.simpleframework.xml;

import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Retention;

/**
 * The <code>ElementList</code> annotation represents a method or
 * field that is a <code>Collection</code> for storing entries. The
 * collection object deserialized is typically of the same type as
 * the field. However, a <code>class</code> attribute can be used to
 * override the field type, however the type must be assignable.
 * <pre>
 * 
 *    <list class="java.util.ArrayList">
 *       <entry name="one"/>
 *       <entry name="two"/>
 *       <entry name="three"/>  
 *    </list>
 * 
 * </pre>
 * If a <code>class</code> attribute is not provided and the type or
 * the field or method is abstract, a suitable match is searched for 
 * from the collections available from the Java collections framework.
 * This annotation can also compose an inline list of XML elements. 
 * An inline list contains no parent or containing element.
 * <pre>
 *
 *    <entry name="one"/>
 *    <entry name="two"/>
 *    <entry name="three"/>  
 * 
 * </pre>
 * The above XML is an example of the output for an inline list of
 * XML elements. In such a list the annotated field or method must
 * not be given a name. Instead the name is acquired from the name of
 * the entry type. For example if the <code>type</code> attribute of
 * this was set to an object <code>example.Entry</code> then the name 
 * of the entry list would be taken as the root name of the object
 * as taken from the <code>Root</code> annotation for that object.
 * 
 * @author Niall Gallagher
 */
@Retention(RetentionPolicy.RUNTIME)
public @interface ElementList {
   
   /**
    * This represents the name of the XML element. Annotated fields
    * can optionally provide the name of the element. If no name is
    * provided then the name of the annotated field or method will
    * be used in its place. The name is provided if the field or
    * method name is not suitable as an XML element name. Also, if
    * the list is inline then this must not be specified.
    * 
    * @return the name of the XML element this represents
    */
   String name() default "";
   
   /**
    * This is used to provide a name of the XML element representing
    * the entry within the list. An entry name is optional and is
    * used when the name needs to be overridden. This also ensures
    * that entry, regardless of type has the same root name.   
    * 
    * @return this returns the entry XML element for each value
    */
   String entry() default "";
   
   /**
    * Represents the type of object the element list contains. This
    * type is used to deserialize the XML elements from the list. 
    * The object typically represents the deserialized type, but can
    * represent a subclass of the type deserialized as determined
    * by the <code>class</code> attribute value for the list. If 
    * this is not specified then the type can be determined from the
    * generic parameter of the annotated <code>Collection</code>.
    * 
    * @return the type of the element deserialized from the XML
    */
   Class type() default void.class;
   
   /**
    * This is used to determine whether the element data is written
    * in a CDATA block or not. If this is set to true then the text
    * is written within a CDATA block, by default the text is output
    * as escaped XML. Typically this is useful when this annotation
    * is applied to an array of primitives, such as strings.
    * 
    * @return true if entries are to be wrapped in a CDATA block
    */
   boolean data() default false;
   
   /**
    * Determines whether the element is required within the XML
    * document. Any field marked as not required will not have its
    * value set when the object is deserialized. If an object is to
    * be serialized only a null attribute will not appear as XML.
    * 
    * @return true if the element is required, false otherwise
    */        
   boolean required() default true;
   
   /**
    * Determines whether the element list is inlined with respect
    * to the parent XML element. An inlined element list does not
    * contain an enclosing element. It is simple a sequence of 
    * elements that appear one after another within an element.
    * As such an inline element list must not have a name. 
    *
    * @return this returns true if the element list is inline
    */
   boolean inline() default false;
   
   /**
    * This is used to determine if an optional field or method can
    * remain null if it does not exist. If this is false then the
    * optional element is given an empty list. This is a convenience
    * attribute which avoids having to check if the element is null
    * before providing it with a suitable default instance.
    * 
    * @return false if an optional element is always instantiated
    */
   boolean empty() default true;
}