hash function to generate hash value with only 5 digits in java

Question

I have used hashCode() method from String API and it is generating value as 99162322 for the below code:

String str = "hello";           
System.out.println(str.hashCode());

Is there any Java API which generate a hash value with only 5 digits (63346) like Oracle SQL as below?

select ORA_HASH('hello','99999') from dual  --63346

Answer 1

Oracle's ora_hash function is designed to provide a hash code for distributing items into buckets efficiently. That makes the purpose of the function with no maximum equivalent to the purpose Java's hashCode() method.

It appears that in Oracle the maximum value argument just takes the modulus of the hash code by the maximum value + 1.

SQL> select ora_hash('hello', 49999) from dual;

ORA_HASH('HELLO',49999)
-----------------------
                  13346

In Java, to provide an equivalent value, you can obtain the remainder of dividing the hash code by that maximum value plus one.

int hash = str.hashCode() % (max + 1);  // max could be 99999

However, the hashing algorithms for String and Oracle are different, so the values will differ.

String s = "hello";
System.out.println(s.hashCode() % 100000);

Output:

62322

Also, the range of a Java hash code is that of a signed int, and the range of ora_hash is that of an unsigned integer.

Answer 2

Not really sure why you need this, but you could MOD the result, for example...

String h = "blah";

int hash = h.hashCode() % 100000; // Would give numbers from 0-99999
int hash = h.hashCode() % 10000; // Would give numbers from 0-9999

I suppose you need it to return exactly the same number as the Oracle function thought right?