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
018package org.apache.commons.math3.geometry.spherical.twod;
019
020import java.io.Serializable;
021
022import org.apache.commons.math3.geometry.Space;
023import org.apache.commons.math3.geometry.spherical.oned.Sphere1D;
024
025/**
026 * This class implements a two-dimensional sphere (i.e. the regular sphere).
027 * <p>
028 * We use here the topologists definition of the 2-sphere (see
029 * <a href="http://mathworld.wolfram.com/Sphere.html">Sphere</a> on
030 * MathWorld), i.e. the 2-sphere is the two-dimensional surface
031 * defined in 3D as x<sup>2</sup>+y<sup>2</sup>+z<sup>2</sup>=1.
032 * </p>
033 * @since 3.3
034 */
035public class Sphere2D implements Serializable, Space {
036
037    /** Serializable version identifier. */
038    private static final long serialVersionUID = 20131218L;
039
040    /** Private constructor for the singleton.
041     */
042    private Sphere2D() {
043    }
044
045    /** Get the unique instance.
046     * @return the unique instance
047     */
048    public static Sphere2D getInstance() {
049        return LazyHolder.INSTANCE;
050    }
051
052    /** {@inheritDoc} */
053    public int getDimension() {
054        return 2;
055    }
056
057    /** {@inheritDoc} */
058    public Sphere1D getSubSpace() {
059        return Sphere1D.getInstance();
060    }
061
062    // CHECKSTYLE: stop HideUtilityClassConstructor
063    /** Holder for the instance.
064     * <p>We use here the Initialization On Demand Holder Idiom.</p>
065     */
066    private static class LazyHolder {
067        /** Cached field instance. */
068        private static final Sphere2D INSTANCE = new Sphere2D();
069    }
070    // CHECKSTYLE: resume HideUtilityClassConstructor
071
072    /** Handle deserialization of the singleton.
073     * @return the singleton instance
074     */
075    private Object readResolve() {
076        // return the singleton instance
077        return LazyHolder.INSTANCE;
078    }
079
080}