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feilong is a suite of core and expanded libraries that include utility classes, http, excel,cvs, io classes, and much much more.

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/*
 * Copyright (C) 2008 feilong
 *
 * 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.feilong.lib.json;

/**
 * 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{

    /** The Constant serialVersionUID. */
    private static final long serialVersionUID = 7216124736163645852L;

    /** singleton instance. */
    private static JSONNull   instance;

    //---------------------------------------------------------------

    static{
        instance = new JSONNull();
    }

    //---------------------------------------------------------------

    /**
     * Returns the singleton instance of JSONNull.
     *
     * @return the singleton instance
     */
    public static JSONNull getInstance(){
        return instance;
    }

    /**
     * Instantiates a new JSON null.
     */
    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.
     */
    @Override
    public boolean equals(Object object){
        return object == null || //
                        object == this || //
                        object == instance || //
                        (object instanceof JSONObject && ((JSONObject) object).isNullObject()) || //
                        "null".equals(object);
    }

    //---------------------------------------------------------------

    /**
     * Hash code.
     *
     * @return the int
     */
    @Override
    public int hashCode(){
        return 37 + "null".hashCode();
    }

    //---------------------------------------------------------------

    /**
     * Size.
     *
     * @return the int
     */
    @Override
    public int size(){
        throw new JSONException("Object is null");
    }

    //---------------------------------------------------------------

    /**
     * Get the "null" string value.
     *
     * @return The string "null".
     */
    @Override
    public String toString(){
        return "null";
    }

    /**
     * To string.
     *
     * @param indentFactor
     *            the indent factor
     * @param indent
     *            the indent
     * @return the string
     */
    @Override
    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();
    }

}