# AbstractXReference.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.pdfparser.xref;

    import org.apache.pdfbox.pdfparser.PDFXRefStream;

    /**
     * An extending class represents an entry, as it can be found in a PDF's crossreference stream ({@link PDFXRefStream}).
     * Such an entry shall locate a PDF object/resource in a PDF document.
     *
     * @author Christian Appl
     */
    public abstract class AbstractXReference implements XReferenceEntry
    {

        private final XReferenceType type;

        /**
         * Creates a crossreference stream entry of the given {@link XReferenceType}.
         *
         * @param type The {@link XReferenceType} of the crossreference stream entry.
         */
        protected AbstractXReference(XReferenceType type)
        {
            this.type = type;
        }

        /**
         * Returns the {@link XReferenceType} of this crossreference stream entry.
         *
         * @return The {@link XReferenceType} of this crossreference stream entry.
         */
        @Override
        public XReferenceType getType()
        {
            return type;
        }

        /**
         * Returns the value for the first column of the crossreference stream entry. (The numeric representation of this
         * entry's (The numeric representation of this entry's {@link XReferenceType}.)
         *
         * @return The value for the first column of the crossreference stream entry.
         */
        @Override
        public long getFirstColumnValue()
        {
            return getType().getNumericValue();
        }

        /**
         * Compares this object with the specified object for order. Returns a negative integer, zero, or a positive integer
         * as this object is less than, equal to, or greater than the specified object.
         *
         * @param xReferenceEntry the object to be compared.
         * @return a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than
         * the specified object.
         */
        @Override
        public int compareTo(XReferenceEntry xReferenceEntry)
        {
            if (getReferencedKey() == null)
            {
                return -1;
            }
            else if (xReferenceEntry == null || xReferenceEntry.getReferencedKey() == null)
            {
                return 1;
            }

            return getReferencedKey().compareTo(xReferenceEntry.getReferencedKey());
        }
    }