# COSNull.java

    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You 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.apache.pdfbox.cos;

    import java.io.IOException;
    import java.io.OutputStream;

    /**
     * This class represents a null PDF object.
     *
     * @author Ben Litchfield
     */
    public final class COSNull extends COSBase
    {
        /**
         * The null token.
         */
        public static final byte[] NULL_BYTES = new byte[] {110, 117, 108, 108}; //"null".getBytes( "ISO-8859-1" );

        /**
         * The one null object in the system.
         */
        public static final COSNull NULL = new COSNull();

        /**
         * Constructor.
         */
        private COSNull()
        {
            //limit creation to one instance.
        }

        /**
         * Visitor pattern double dispatch method.
         *
         * @param visitor The object to notify when visiting this object.
         * @throws IOException If an error occurs while visiting this object.
         */
        @Override
        public void accept(ICOSVisitor visitor) throws IOException
        {
            visitor.visitFromNull(this);
        }

        /**
         * This will output this string as a PDF object.
         *
         * @param output The stream to write to.
         * @throws IOException If there is an error writing to the stream.
         */
        public void writePDF( OutputStream output ) throws IOException
        {
            output.write(NULL_BYTES);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public String toString()
        {
            return "COSNull{}";
        }
    }