[Solved] Java hashing function to return int that does not exceed Integer.MAX_VALUE [closed]

Question

1
The methods you used were for returning longs. The method you should use is String.hashCode() if you don’t need hashing for security purposes. Make sure to cast an integer as a String through String.valueOf(int) before hashing it, since you said you want to hash ints as well.

int hash = String.valueOf(input).hashCode();

2
Edit: Added MD5 info after OP requested in comment

I have a class that can take an input String, process it through MD5, and convert it to a long, though I don’t know how to convert it to an int. What you can do is return the long, and truncate it to only 10 characters for an int. Here is the class:

import java.security.*;

public class HX {

  final String seed;
  final MessageDigest md;
  final long hash;

  public HX(String s) throws NoSuchAlgorithmException {

   seed = s;
    md = MessageDigest.getInstance("MD5");
    hash = computeHash();
  }

  public long getHash() {
    return hash;
  }

  public long computeHash() {
    md.reset();
    final byte[] digest = md.digest(seed.getBytes());
    return (computeHash(digest, 0) ^ computeHash(digest, 8));
  }

  private static final long computeHash(final byte[] array, final int offset) {
    long value = 0;
    for (int i = 0; i < 8; i++) {
       value = ((value << 8) | (array[offset+i] & 0xFF));
    }
    return value;
   }
}

It could still exceed the MAX_VALUE after truncation, however, so if that’s the case, you’d need to truncate it an int of length 9.

long longHash = 0;
try {
     HX h = new HX(seed);
     longHash = h.getHash();
} catch(Exception e) {
     e.printStackTrace();
}

try {
  int hash = Integer.parseInt(longHash.substring(0,9));
} catch(Exception e) {
  int hash = Integer.parseInt(longHash.substring(0,8));
}

3
If you’d like an alternative to MD5, I have a method I downloaded a long time ago from a post by a guy claiming that his “better hash” reduced collisions; some tests with a list of thousands of dictionary words appeared to have confirmed this, from what I recall.

public static int hash(String s) {
  int hash = 0;
  for (int i = 0; i < s.length(); i++) {
      hash = 257*hash + s.charAt(i);
  }
  return h;
}

Accepted Answer