How to implement a hash function for a point on a grid

Question

I need a hash function to overide the hashCode() method from the object class.

I have a Point class that represents a point on coordinate grid. The instance variables are double x, y;

I also have methods

public int getX(){
 return Math.round(x);
}

public int getY(){
   Math.round(y);
}

How can I create a hash function that will return an integer? Would a simply put

return Math.round(getX()/getY());

work?

The aim of a hash function is to uniformly distribute values between 0 and 2^32 - 1. Does your function do that? — Oliver Charlesworth, Jan 25 '14 at 21:24
Well how are you defining equality, first? Why do you have `double` variables if you're rounding in the getters? Are they actually intended to be more than integers, usefully? — Jon Skeet, Jan 25 '14 at 21:24
There are going to be a lot of hash collisions if you do it this way... For example, 6/3 = 2 and 4/2 = 2; — 1110101001, Jan 25 '14 at 21:25

score 1 · Answer 1 · edited May 23 '17 at 10:25

1

Your IDE most likely has a utility to generate hash code and equals for you, look under the source or insert code menus.

All you need to do though is return getX()+31*getY();

See this question and answer for more detailed discussion on the theory of hash codes:

edited May 23 '17 at 10:25

Community

answered Jan 25 '14 at 21:27

Tim B

1 Answers1