????????????????????????????????????????????????

Point p1 = new Point(1?? 2);
Point p2 = new Point(1?? 2);

Point q = new Point(2?? 3);

System.out.println(p1.equals(p2)); // prints true

System.out.println(p1.equals(q)); // prints false

???????????????????????Point?????????????????????????????

import java.util.HashSet;

HashSet coll = new HashSet();
coll.add(p1);

System.out.println(coll.contains(p2)); // prints false

???????coll????а???p2?????????p1?????????????棬p1??p2???????????????????????У??????????????е??Щ???????p2a????????p2?????????p2a????????Object????Point?????

Object p2a = p2;

??????????????????????????????????p2????p2a??????????????μ?????

System.out.println(p1.equals(p2a)); // prints false

???????????????????????????????????????equals?汾????и???Object???equals???????????????????????????Object??equals?????????

public boolean equals(Object other)

???????Point???е?equals????????????Point?????Object????????????????????и???Object?е?equals?????????????仯??????????Java????????????????????????????????????????????????????????Point??Point??equals?????????á???????????????????Object???Object???equals?????á???????????????б???????????????????????????????????????p1??p2a?????????x??y???”p1.equals(p2a)”?????????false??????????HasSet??contains????????false?????????????????????????????????????????Object??equals????????Point????仯??????????equals

????????????????????equals???????????￡?

// A better definition?? but still not perfect
@Override public boolean equals(Object other) {
    boolean result = false;
    if (other instanceof Point) {
        Point that = (Point) other;
        result = (this.getX() == that.getX() && this.getY() == that.getY());
    }
    return result;
}

????????equals????????????????????????Object??????????????????????????????????????????instanceof?????????????????????????????????????????Point??????????????????????????????????????false??