/*

  * Copyright 2002-2009 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;

 import java.io.IOException;

 import java.io.Writer;

 /**

  * JSONNull is equivalent to the value that JavaScript calls null, whilst Java's

  * null is equivalent to the value that JavaScript calls undefined.

  *

  * @author JSON.org

  */

 public final class JSONNull implements JSON {

    /** singleton instance */

    private static JSONNull instance;

    static{

       instance = new JSONNull();

    }

    /**

     * Returns the singleton instance of JSONNull

     */

    public static JSONNull getInstance() {

       return instance;

    }

    private JSONNull() {

    }

    /**

     * A Null object is equal to the null value and to itself.

     *

     * @param object An object to test for nullness.

     * @return true if the object parameter is the JSONObject.NULL object or

     *         null.

     */

    public boolean equals( Object object ) {

       return object == null || object == this || object == instance

             || (object instanceof JSONObject && ((JSONObject) object).isNullObject())

             || "null".equals( object );

    }

    public int hashCode() {

       return 37 + "null".hashCode();

    }

    public boolean isArray() {

       return false;

    }

    public boolean isEmpty() {

       throw new JSONException( "Object is null" );

    }

    public int size() {

       throw new JSONException( "Object is null" );

    }

    /**

     * Get the "null" string value.

     *

     * @return The string "null".

     */

    public String toString() {

       return "null";

    }

    public String toString( int indentFactor ) {

       return toString();

    }

    public String toString( int indentFactor, int indent ) {

       StringBuffer sb = new StringBuffer();

       for( int i = 0; i < indent; i += 1 ){

          sb.append( ' ' );

       }

       sb.append( toString() );

       return sb.toString();

    }

    public Writer write( Writer writer ) {

       try{

          writer.write( toString() );

          return writer;

       }catch( IOException e ){

          throw new JSONException( e );

       }

    }

 }