code: /*******************************************************************************
   * Copyright (c) 2015 Voyager Search and MITRE
   * All rights reserved. This program and the accompanying materials
   * are made available under the terms of the Apache License, Version 2.0 which
   * accompanies this distribution and is available at
   *    http://www.apache.org/licenses/LICENSE-2.0.txt
   ******************************************************************************/
  
  package org.locationtech.spatial4j.shape;
  
  import org.locationtech.spatial4j.context.SpatialContext;
  
  /**
   * The base interface defining a geometric shape. Shape instances should be
   * instantiated via one of the create* methods on a {@link SpatialContext} or
   * by reading WKT which calls those methods; they should <em>not</em> be
   * created directly.
   * <p>
   * Shapes are generally immutable and thread-safe. If a particular shape has a
   * <code>reset(...)</code> method then its use means the shape is actually
   * mutable. Mutating shape state is considered expert and should be done with care.
   */
  public interface Shape {
  
    /**
     * Describe the relationship between the two objects.  For example
     * <ul>
     *   <li>this is WITHIN other</li>
     *   <li>this CONTAINS other</li>
     *   <li>this is DISJOINT other</li>
     *   <li>this INTERSECTS other</li>
     * </ul>
     * Note that a Shape implementation may choose to return INTERSECTS when the
     * true answer is WITHIN or CONTAINS for performance reasons. If a shape does
     * this then it <i>must</i> document when it does.  Ideally the shape will not
     * do this approximation in all circumstances, just sometimes.
     * <p>
     * If the shapes are equal then the result is CONTAINS (preferred) or WITHIN.
     */
    SpatialRelation relate(Shape other);
  
    /**
     * Get the bounding box for this Shape. This means the shape is within the
     * bounding box and that it touches each side of the rectangle.
     * <p>
     * Postcondition: <code>this.getBoundingBox().relate(this) == CONTAINS</code>
     */
    Rectangle getBoundingBox();
  
    /**
     * Does the shape have area?  This will be false for points and lines. It will
     * also be false for shapes that normally have area but are constructed in a
     * degenerate case as to not have area (e.g. a circle with 0 radius or
     * rectangle with no height or no width).
     */
    boolean hasArea();
  
    /**
     * Calculates the area of the shape, in square-degrees. If ctx is null then
     * simple Euclidean calculations will be used.  This figure can be an
     * estimate.
     */
    double getArea(SpatialContext ctx);
  
    /**
     * Returns the center point of this shape. This is usually the same as
     * <code>getBoundingBox().getCenter()</code> but it doesn't have to be.
     * <p>
     * Postcondition: <code>this.relate(this.getCenter()) == CONTAINS</code>
     */
    Point getCenter();
  
    /**
     * Returns a buffered version of this shape.  The buffer is usually a
     * rounded-corner buffer, although some shapes might buffer differently. This
     * is an optional operation.
     *
     * @return Not null, and the returned shape should contain the current shape.
     */
    Shape getBuffered(double distance, SpatialContext ctx);
  
    /**
     * Shapes can be "empty", which is to say it exists nowhere. The underlying coordinates are
     * typically NaN.
     */
    boolean isEmpty();
  
    /** The sub-classes of Shape generally implement the
     * same contract for {@link Object#equals(Object)} and {@link Object#hashCode()}
     * amongst the same sub-interface type.  This means, for example, that multiple
     * Point implementations of different classes are equal if they share the same x
     * &amp; y. */
    @Override
    public boolean equals(Object other);
    
    
    /**
     * Get the SpatialContext that created the Shape
     */
    public SpatialContext getContext();
  }
  
  