how to generate hashcode

1. Store some constant nonzero value, say 17, in an int variable called result.
2. For each significant field f in your object (each field taken into account by the
equals method, that is), do the following:
a. Compute an int hash code c for the field:
i. If the field is a boolean, compute (f ? 0 : 1).
ii. If the field is a byte, char, short, or int, compute (int)f.
iii. If the field is a long, compute (int)(f ^ (f >>> 32)).
iv. If the field is a float compute Float.floatToIntBits(f).
v. If the field is a double, compute Double.doubleToLongBits(f), and
then hash the resulting long as in step 2.a.iii.
vi. If the field is an object reference and this class’s equals method
compares the field by recursively invoking equals, recursively
invoke hashCode on the field. If a more complex comparison is
required, compute a “canonical representation” for this field and
invoke hashCode on the canonical representation. If the value of the
field is null, return 0 (or some other constant, but 0 is traditional).
vii. If the field is an array, treat it as if each element were a separate field.
That is, compute a hash code for each significant element by applying
these rules recursively, and combine these values as described in
step 2.b.
b. Combine the hash code c computed in step a into result as follows:
result = 37*result + c;
3. Return result.
4. When you are done writing the hashCode method, ask yourself whether equal
instances have equal hash codes. If not, figure out why and fix the problem.