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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
/** * 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.
/** * 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 x and affine y-coordinate y.
Params:
  • x – the affine x-coordinate.
  • y – the affine y-coordinate.
Throws:
/** * Creates an ECPoint from the specified affine x-coordinate * <code>x</code> and affine y-coordinate <code>y</code>. * @param x the affine x-coordinate. * @param y the affine y-coordinate. * @exception NullPointerException if <code>x</code> or * <code>y</code> 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 x. Note: POINT_INFINITY has a null affine x-coordinate.
Returns:the affine x-coordinate.
/** * Returns the affine x-coordinate <code>x</code>. * Note: POINT_INFINITY has a null affine x-coordinate. * @return the affine x-coordinate. */
public BigInteger getAffineX() { return x; }
Returns the affine y-coordinate y. Note: POINT_INFINITY has a null affine y-coordinate.
Returns:the affine y-coordinate.
/** * Returns the affine y-coordinate <code>y</code>. * 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.
Params:
  • obj – the object to be compared.
Returns:true if obj is an instance of ECPoint and the affine coordinates match, false otherwise.
/** * Compares this elliptic curve point for equality with * the specified object. * @param obj the object to be compared. * @return true if <code>obj</code> 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.
Returns:a hash code value.
/** * 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(); } }