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Java library for transforming beans, maps, collections, java arrays and XML to JSON.
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/*
 * Copyright 2002-2007 the original author or authors.
 *
 * 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 net.sf.json.util;

import net.sf.json.JSONArray;
import net.sf.json.JSONException;
import net.sf.json.JSONObject;

/**
 * Base class for cycle detection in a hierarchy.

 * The JSON spec forbides cycles in a hierarchy and most parsers will raise and
 * error when a cycle is detected. This class defines a contract for handling
 * those cycles and two base implementations:
 * 
 * STRICT - will throw a JSONException if a cycle is found.
 * LENIENT - will return an empty array or null object if a cycle is found.
 * 
 *
 * @author Andres Almiray 
 */
public abstract class CycleDetectionStrategy {
   /** Returns empty array and null object */
   public static final CycleDetectionStrategy LENIENT = new LenientCycleDetectionStrategy();
   /** Throws a JSONException */
   public static final CycleDetectionStrategy STRICT = new StrictCycleDetectionStrategy();

   /**
    * Handle a repeated reference

    * Must return a valid JSONArray or null.
    *
    * @param reference the repeated reference.
    */
   public abstract JSONArray handleRepeatedReferenceAsArray( Object reference );

   /**
    * Handle a repeated reference

    * Must return a valid JSONObject or null.
    *
    * @param reference the repeated reference.
    */
   public abstract JSONObject handleRepeatedReferenceAsObject( Object reference );

   private static final class LenientCycleDetectionStrategy extends CycleDetectionStrategy {
      public JSONArray handleRepeatedReferenceAsArray( Object reference ) {
         return new JSONArray();
      }

      public JSONObject handleRepeatedReferenceAsObject( Object reference ) {
         return new JSONObject( true );
      }
   }

   private static final class StrictCycleDetectionStrategy extends CycleDetectionStrategy {
      public JSONArray handleRepeatedReferenceAsArray( Object reference ) {
         throw new JSONException( "There is a cycle in the hierarchy!" );
      }

      public JSONObject handleRepeatedReferenceAsObject( Object reference ) {
         throw new JSONException( "There is a cycle in the hierarchy!" );
      }
   }
}