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/*
* 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.commons.math3.geometry.spherical.twod;
import java.io.Serializable;
import org.apache.commons.math3.geometry.Space;
import org.apache.commons.math3.geometry.spherical.oned.Sphere1D;
/**
* This class implements a two-dimensional sphere (i.e. the regular sphere).
* <p>
* We use here the topologists definition of the 2-sphere (see
* <a href="http://mathworld.wolfram.com/Sphere.html">Sphere</a> on
* MathWorld), i.e. the 2-sphere is the two-dimensional surface
* defined in 3D as x<sup>2</sup>+y<sup>2</sup>+z<sup>2</sup>=1.
* </p>
* @since 3.3
*/
public class Sphere2D implements Serializable, Space {
/** Serializable version identifier. */
private static final long serialVersionUID = 20131218L;
/** Private constructor for the singleton.
*/
private Sphere2D() {
}
/** Get the unique instance.
* @return the unique instance
*/
public static Sphere2D getInstance() {
return LazyHolder.INSTANCE;
}
/** {@inheritDoc} */
public int getDimension() {
return 2;
}
/** {@inheritDoc} */
public Sphere1D getSubSpace() {
return Sphere1D.getInstance();
}
// CHECKSTYLE: stop HideUtilityClassConstructor
/** Holder for the instance.
* <p>We use here the Initialization On Demand Holder Idiom.</p>
*/
private static class LazyHolder {
/** Cached field instance. */
private static final Sphere2D INSTANCE = new Sphere2D();
}
// CHECKSTYLE: resume HideUtilityClassConstructor
/** Handle deserialization of the singleton.
* @return the singleton instance
*/
private Object readResolve() {
// return the singleton instance
return LazyHolder.INSTANCE;
}
}
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