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13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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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
ECPoint()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} and affine y-coordinate {@code y}.
58      * @param x the affine x-coordinate.
59      * @param y the affine y-coordinate.
60      * @exception NullPointerException if {@code x} or
61      * {@code y} is null.
62      */
ECPoint(BigInteger x, BigInteger y)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}.
73      * Note: POINT_INFINITY has a null affine x-coordinate.
74      * @return the affine x-coordinate.
75      */
getAffineX()76     public BigInteger getAffineX() {
77         return x;
78     }
79 
80     /**
81      * Returns the affine y-coordinate {@code y}.
82      * Note: POINT_INFINITY has a null affine y-coordinate.
83      * @return the affine y-coordinate.
84      */
getAffineY()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} is an instance of
94      * ECPoint and the affine coordinates match, false otherwise.
95      */
equals(Object obj)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      */
hashCode()110     public int hashCode() {
111         if (this == POINT_INFINITY) return 0;
112         return x.hashCode() << 5 + y.hashCode();
113     }
114 }
115