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    1   /*
    2    * Copyright (c) 2003, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   package java.security.spec;
   26   
   27   import java.math.BigInteger;
   28   
   29   /**
   30    * This immutable class represents a point on an elliptic curve (EC)
   31    * in affine coordinates. Other coordinate systems can
   32    * extend this class to represent this point in other
   33    * coordinates.
   34    *
   35    * @author Valerie Peng
   36    *
   37    * @since 1.5
   38    */
   39   public class ECPoint {
   40   
   41       private final BigInteger x;
   42       private final BigInteger y;
   43   
   44       /**
   45        * This defines the point at infinity.
   46        */
   47       public static final ECPoint POINT_INFINITY = new ECPoint();
   48   
   49       // private constructor for constructing point at infinity
   50       private ECPoint() {
   51           this.x = null;
   52           this.y = null;
   53       }
   54   
   55       /**
   56        * Creates an ECPoint from the specified affine x-coordinate
   57        * <code>x</code> and affine y-coordinate <code>y</code>.
   58        * @param x the affine x-coordinate.
   59        * @param y the affine y-coordinate.
   60        * @exception NullPointerException if <code>x</code> or
   61        * <code>y</code> is null.
   62        */
   63       public ECPoint(BigInteger x, BigInteger y) {
   64           if ((x==null) || (y==null)) {
   65               throw new NullPointerException("affine coordinate x or y is null");
   66           }
   67           this.x = x;
   68           this.y = y;
   69       }
   70   
   71       /**
   72        * Returns the affine x-coordinate <code>x</code>.
   73        * Note: POINT_INFINITY has a null affine x-coordinate.
   74        * @return the affine x-coordinate.
   75        */
   76       public BigInteger getAffineX() {
   77           return x;
   78       }
   79   
   80       /**
   81        * Returns the affine y-coordinate <code>y</code>.
   82        * Note: POINT_INFINITY has a null affine y-coordinate.
   83        * @return the affine y-coordinate.
   84        */
   85       public BigInteger getAffineY() {
   86           return y;
   87       }
   88   
   89       /**
   90        * Compares this elliptic curve point for equality with
   91        * the specified object.
   92        * @param obj the object to be compared.
   93        * @return true if <code>obj</code> is an instance of
   94        * ECPoint and the affine coordinates match, false otherwise.
   95        */
   96       public boolean equals(Object obj) {
   97           if (this == obj) return true;
   98           if (this == POINT_INFINITY) return false;
   99           if (obj instanceof ECPoint) {
  100               return ((x.equals(((ECPoint)obj).x)) &&
  101                       (y.equals(((ECPoint)obj).y)));
  102           }
  103           return false;
  104       }
  105   
  106       /**
  107        * Returns a hash code value for this elliptic curve point.
  108        * @return a hash code value.
  109        */
  110       public int hashCode() {
  111           if (this == POINT_INFINITY) return 0;
  112           return x.hashCode() << 5 + y.hashCode();
  113       }
  114   }

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