content: /*
   * CoversionInstance.java April 2007
   *
   * Copyright (C) 2007, 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 com.aliyun.odps.simpleframework.xml.core;
  
  import com.aliyun.odps.simpleframework.xml.strategy.Value;
  
  /**
   * The <code>ConversionInstance</code> object is used to promote the
   * type to some more specialized type. For example if a field or 
   * method that represents a <code>List</code> is annotated then this
   * might create a specialized type such as a <code>Vector</code>. It
   * typically used to promote a type either because it is abstract
   * or because another type is required. 
   * <p>
   * This is used by the <code>CollectionFactory</code> to convert the
   * type of a collection field from an abstract type to a instantiable
   * type. This is used to simplify strategy implementations. 
   *
   * @author Niall Gallagher
   * 
   * @see CollectionFactory
   */
  class ConversionInstance implements Instance {
     
     /**
      * This is the context that is used to create the instance.
      */
     private final Context context;
     
     /**
      * This is the new class that is used for the type conversion. 
      */
     private final Class convert;
     
     /**
      * This is the value object that will be wrapped by this.
      */
     private final Value value;
     
     /**
      * This is used to specify the creation of a conversion type that
      * can be used for creating an instance with a class other than 
      * the default class specified by the <code>Value</code> object.
      * 
      * @param context this is the context used for instantiation
      * @param value this is the type used to create the instance
      * @param convert this is the class the type is converted to
      */
     public ConversionInstance(Context context, Value value, Class convert) throws Exception {
        this.context = context;
        this.convert = convert;      
        this.value = value;
     }
     
     /**
      * This method is used to acquire an instance of the type that
      * is defined by this object. If for some reason the type can
      * not be instantiated an exception is thrown from this.
      * 
      * @return an instance of the type this object represents
      */
     public Object getInstance() throws Exception {
        if(value.isReference()) {
           return value.getValue();
        }
        Object created = getInstance(convert);
        
        if(created != null) {
           setInstance(created);
        }
        return created;
     }
  
     /**
      * This method is used to acquire an instance of the type that
      * is defined by this object. If for some reason the type can
      * not be instantiated an exception is thrown from this.
      * 
      * @param type this is the type of the instance to create
      * 
      * @return an instance of the type this object represents
      */
     public Object getInstance(Class type) throws Exception {
        Instance value = context.getInstance(type);
        Object object = value.getInstance();
        
        return object;
     }
     
     /**
      * This method is used acquire the value from the type and if
      * possible replace the value for the type. If the value can
      * not be replaced then an exception should be thrown. This 
      * is used to allow primitives to be inserted into a graph.
      * 
      * @param object this is the object to insert as the value
      * 
      * @return an instance of the type this object represents
      */
     public Object setInstance(Object object) throws Exception {
        if(value != null) {
           value.setValue(object);
        }
        return object;
     }
     
     /**
      * This is the type of the object instance that will be created
      * by the <code>getInstance</code> method. This allows the 
      * deserialization process to perform checks against the field.
      * 
      * @return the type of the object that will be instantiated
      */
     public Class getType() {
        return convert;
     }
     
     /**
      * This will return true if the <code>Value</code> object provided
      * is a reference type. Typically a reference type refers to a 
      * type that is substituted during the deserialization process 
      * and so constitutes an object that does not need initialization.
      * 
      * @return this returns true if the type is a reference type
      */
     public boolean isReference() {
        return value.isReference();
     }   
  }
  