So for a given prime number 31, how can I write a hash function for a string parameter?

Here is my attempt.

    private int hash(String key){
        int c = 31;
        int hash = 0;
    
        for (int i = 0; i < key.length(); i   ) {
            int ascii = key.charAt(i);
            hash  = c * hash   ascii; 
    }
        return (hash % sizetable);} // sizetable is an integer which is declared outside. You can see it as a table.length().

So, since I can not run any other function in my work and I need to be sure about the process here, I need your answers and help! Thank you so much.

CodePudding user response：

Your implementation looks quite similar to what is documented as standard String.hashCode() implementation, this even uses also 31 as prime factor, so it should be good enough.

I just would not assign 31 to a variable, but declare a private static final field or use it directly as magic number - not OK in general, but might be OK in this case.

Additionally you should add some tests - if you already know about the concept of unit tests - to prove that your method gives different hashes for different strings. And pick the samples clever, so they are different (for the case of the homework ;)