    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.math3.ode.sampling;
    019
    020    /**
    021     * This class is a step handler that does nothing.
    022
    023     * <p>This class is provided as a convenience for users who are only
    024     * interested in the final state of an integration and not in the
    025     * intermediate steps. Its handleStep method does nothing.</p>
    026     *
    027     * <p>Since this class has no internal state, it is implemented using
    028     * the Singleton design pattern. This means that only one instance is
    029     * ever created, which can be retrieved using the getInstance
    030     * method. This explains why there is no public constructor.</p>
    031     *
    032     * @see StepHandler
    033     * @version $Id: DummyStepHandler.java 1416643 2012-12-03 19:37:14Z tn $
    034     * @since 1.2
    035     */
    036
    037    public class DummyStepHandler implements StepHandler {
    038
    039        /** Private constructor.
    040         * The constructor is private to prevent users from creating
    041         * instances (Singleton design-pattern).
    042         */
    043        private DummyStepHandler() {
    044        }
    045
    046        /** Get the only instance.
    047         * @return the only instance
    048         */
    049        public static DummyStepHandler getInstance() {
    050            return LazyHolder.INSTANCE;
    051        }
    052
    053        /** {@inheritDoc} */
    054        public void init(double t0, double[] y0, double t) {
    055        }
    056
    057        /**
    058         * Handle the last accepted step.
    059         * This method does nothing in this class.
    060         * @param interpolator interpolator for the last accepted step. For
    061         * efficiency purposes, the various integrators reuse the same
    062         * object on each call, so if the instance wants to keep it across
    063         * all calls (for example to provide at the end of the integration a
    064         * continuous model valid throughout the integration range), it
    065         * should build a local copy using the clone method and store this
    066         * copy.
    067         * @param isLast true if the step is the last one
    068         */
    069        public void handleStep(final StepInterpolator interpolator, final boolean isLast) {
    070        }
    071
    072        // CHECKSTYLE: stop HideUtilityClassConstructor
    073        /** Holder for the instance.
    074         * <p>We use here the Initialization On Demand Holder Idiom.</p>
    075         */
    076        private static class LazyHolder {
    077            /** Cached field instance. */
    078            private static final DummyStepHandler INSTANCE = new DummyStepHandler();
    079        }
    080        // CHECKSTYLE: resume HideUtilityClassConstructor
    081
    082        /** Handle deserialization of the singleton.
    083         * @return the singleton instance
    084         */
    085        private Object readResolve() {
    086            // return the singleton instance
    087            return LazyHolder.INSTANCE;
    088        }
    089
    090    }