    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one or more
    003     * contributor license agreements.  See the NOTICE file distributed with
    004     * this work for additional information regarding copyright ownership.
    005     * The ASF licenses this file to You under the Apache License, Version 2.0
    006     * (the "License"); you may not use this file except in compliance with
    007     * the License.  You may obtain a copy of the License at
    008     *
    009     *      http://www.apache.org/licenses/LICENSE-2.0
    010     *
    011     * Unless required by applicable law or agreed to in writing, software
    012     * distributed under the License is distributed on an "AS IS" BASIS,
    013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014     * See the License for the specific language governing permissions and
    015     * limitations under the License.
    016     */
    017
    018    package org.apache.commons.math.fraction;
    019
    020    import java.io.Serializable;
    021
    022    import org.apache.commons.math.Field;
    023
    024    /**
    025     * Representation of the fractional numbers field.
    026     * <p>
    027     * This class is a singleton.
    028     * </p>
    029     * @see Fraction
    030     * @version $Revision: 811827 $ $Date: 2009-09-06 17:32:50 +0200 (dim. 06 sept. 2009) $
    031     * @since 2.0
    032     */
    033    public class FractionField implements Field<Fraction>, Serializable  {
    034
    035        /** Serializable version identifier */
    036        private static final long serialVersionUID = -1257768487499119313L;
    037
    038        /** Private constructor for the singleton.
    039         */
    040        private FractionField() {
    041        }
    042
    043        /** Get the unique instance.
    044         * @return the unique instance
    045         */
    046        public static FractionField getInstance() {
    047            return LazyHolder.INSTANCE;
    048        }
    049
    050        /** {@inheritDoc} */
    051        public Fraction getOne() {
    052            return Fraction.ONE;
    053        }
    054
    055        /** {@inheritDoc} */
    056        public Fraction getZero() {
    057            return Fraction.ZERO;
    058        }
    059
    060        // CHECKSTYLE: stop HideUtilityClassConstructor
    061        /** Holder for the instance.
    062         * <p>We use here the Initialization On Demand Holder Idiom.</p>
    063         */
    064        private static class LazyHolder {
    065            /** Cached field instance. */
    066            private static final FractionField INSTANCE = new FractionField();
    067        }
    068        // CHECKSTYLE: resume HideUtilityClassConstructor
    069
    070        /** Handle deserialization of the singleton.
    071         * @return the singleton instance
    072         */
    073        private Object readResolve() {
    074            // return the singleton instance
    075            return LazyHolder.INSTANCE;
    076        }
    077
    078    }