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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  package java.security.spec;
  
  import java.math.BigInteger;
  
  /**
   * This immutable class represents a point on an elliptic curve (EC)
   * in affine coordinates. Other coordinate systems can
   * extend this class to represent this point in other
   * coordinates.
   *
   * @author Valerie Peng
   *
   * @since 1.5
   */
  public class ECPoint {
  
      private final BigInteger x;
      private final BigInteger y;
  
      /**
       * This defines the point at infinity.
       */
      public static final ECPoint POINT_INFINITY = new ECPoint();
  
      // private constructor for constructing point at infinity
      private ECPoint() {
          this.x = null;
          this.y = null;
      }
  
      /**
       * Creates an ECPoint from the specified affine x-coordinate
       * {@code x} and affine y-coordinate {@code y}.
       * @param x the affine x-coordinate.
       * @param y the affine y-coordinate.
       * @exception NullPointerException if {@code x} or
       * {@code y} is null.
       */
      public ECPoint(BigInteger x, BigInteger y) {
          if ((x==null) || (y==null)) {
              throw new NullPointerException("affine coordinate x or y is null");
          }
          this.x = x;
          this.y = y;
      }
  
      /**
       * Returns the affine x-coordinate {@code x}.
       * Note: POINT_INFINITY has a null affine x-coordinate.
       * @return the affine x-coordinate.
       */
      public BigInteger getAffineX() {
          return x;
      }
  
      /**
       * Returns the affine y-coordinate {@code y}.
       * Note: POINT_INFINITY has a null affine y-coordinate.
       * @return the affine y-coordinate.
       */
      public BigInteger getAffineY() {
          return y;
      }
  
      /**
       * Compares this elliptic curve point for equality with
       * the specified object.
       * @param obj the object to be compared.
       * @return true if {@code obj} is an instance of
       * ECPoint and the affine coordinates match, false otherwise.
       */
      public boolean equals(Object obj) {
          if (this == obj) return true;
          if (this == POINT_INFINITY) return false;
          if (obj instanceof ECPoint) {
              return ((x.equals(((ECPoint)obj).x)) &&
                      (y.equals(((ECPoint)obj).y)));
          }
          return false;
      }
  
      /**
       * Returns a hash code value for this elliptic curve point.
       * @return a hash code value.
       */
      public int hashCode() {
          if (this == POINT_INFINITY) return 0;
          return x.hashCode() << 5 + y.hashCode();
      }
  }
  