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 *

 * 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

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 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

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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.

     * {@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();

    }

}