The best implementation? That is a hard question because it depends on the usage pattern. A for nearly all cases reasonable good implementation was proposed in Josh Bloch‘s Effective Java in Item 8 (second edition). The best thing is to look it up there because the author explains there why the approach is good. A … Read more
Joshua Bloch says on Effective Java You must override hashCode() in every class that overrides equals(). Failure to do so will result in a violation of the general contract for Object.hashCode(), which will prevent your class from functioning properly in conjunction with all hash-based collections, including HashMap, HashSet, and Hashtable. Let’s try to understand it … Read more
The theory (for the language lawyers and the mathematically inclined): equals() (javadoc) must define an equivalence relation (it must be reflexive, symmetric, and transitive). In addition, it must be consistent (if the objects are not modified, then it must keep returning the same value). Furthermore, o.equals(null) must always return false. hashCode() (javadoc) must also be … Read more
Why reinvent the wheel? Give Lodash a try. It has a number of must-have functions such as isEqual(). _.isEqual(object, other); It will brute force check each key value – just like the other examples on this page – using ECMAScript 5 and native optimizations if they’re available in the browser. Note: Previously this answer recommended Underscore.js, … Read more
The MessageDigest class can provide you with an instance of the MD5 digest. When working with strings and the crypto classes be sure to always specify the encoding you want the byte representation in. If you just use string.getBytes() it will use the platform default. (Not all platforms use the same defaults) import java.security.*; .. … Read more
Yes, it is important if your item will be used as a key in a dictionary, or HashSet<T>, etc – since this is used (in the absence of a custom IEqualityComparer<T>) to group items into buckets. If the hash-code for two items does not match, they may never be considered equal (Equals will simply never … Read more
I usually go with something like the implementation given in Josh Bloch’s fabulous Effective Java. It’s fast and creates a pretty good hash which is unlikely to cause collisions. Pick two different prime numbers, e.g. 17 and 23, and do: public override int GetHashCode() { unchecked // Overflow is fine, just wrap { int hash … Read more