Java hashcode reverse calculation

Question

I am trying to test out how String hashcode works by adding a new character and do the reverse to subtract it out, however it didn't give me the right answer when i did the calculation.

For example

int PRIME = 31;

//this will print 1687846330 
System.out.println("mlkjihgfedcb".hashCode());   

//this will print 783628775 which equals to "mlkjihgfedcba".hashCode();
System.out.println(("mlkjihgfedcb".hashCode() * PRIME + (int) 'a')); 

//this will print 25278344 which doesn't equals to "mlkjihgfedcb".hashCode()
System.out.println(("mlkjihgfedcba".hashCode() - (int) 'a') / PRIME);

I am wondering did i do the math right on my last step above ? overflow shouldn't matter for the calculation right ?

Java hashcode reverse calculation

3 Answers