# PDObjectStream.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.pdmodel.common;

    import org.apache.pdfbox.cos.COSName;
    import org.apache.pdfbox.cos.COSStream;

    import org.apache.pdfbox.pdmodel.PDDocument;

    /**
     * A PDStream represents a stream in a PDF document.  Streams are tied to a single
     * PDF document.
     *
     * @author Ben Litchfield
     */
    public class PDObjectStream extends PDStream
    {

        /**
         * Constructor.
         *
         * @param str The stream parameter.
         */
        public PDObjectStream( COSStream str )
        {
            super( str );
        }

        /**
         * This will create a new PDObjectStream object.
         *
         * @param document The document that the stream will be part of.
         * @return A new stream object.
         */
        public static PDObjectStream createStream( PDDocument document )
        {
            COSStream cosStream = document.getDocument().createCOSStream();
            PDObjectStream strm = new PDObjectStream( cosStream );
            strm.getCOSObject().setItem( COSName.TYPE, COSName.OBJ_STM );
            return strm;
        }

        /**
         * Get the type of this object, should always return "ObjStm".
         *
         * @return The type of this object.
         */
        public String getType()
        {
            return getCOSObject().getNameAsString( COSName.TYPE );
        }

        /**
         * Get the number of compressed object.
         *
         * @return The number of compressed objects.
         */
        public int getNumberOfObjects()
        {
            return getCOSObject().getInt( COSName.N, 0 );
        }

        /**
         * Set the number of objects.
         *
         * @param n The new number of objects.
         */
        public void setNumberOfObjects( int n )
        {
            getCOSObject().setInt( COSName.N, n );
        }

        /**
         * The byte offset (in the decoded stream) of the first compressed object.
         *
         * @return The byte offset to the first object.
         */
        public int getFirstByteOffset()
        {
            return getCOSObject().getInt( COSName.FIRST, 0 );
        }

        /**
         * The byte offset (in the decoded stream) of the first compressed object.
         *
         * @param n The byte offset to the first object.
         */
        public void setFirstByteOffset( int n )
        {
            getCOSObject().setInt( COSName.FIRST, n );
        }

        /**
         * A reference to an object stream, of which the current object stream is
         * considered an extension.
         *
         * @return The object that this stream is an extension.
         */
        public PDObjectStream getExtends()
        {
            COSStream stream = getCOSObject().getCOSStream(COSName.EXTENDS);
            return stream != null ? new PDObjectStream(stream) : null;
        }

        /**
         * A reference to an object stream, of which the current object stream is
         * considered an extension.
         *
         * @param stream The object stream extension.
         */
        public void setExtends( PDObjectStream stream )
        {
            getCOSObject().setItem( COSName.EXTENDS, stream );
        }
    }