I was just wondering why is that primes are used in a class’s hashCode() method? For example, when using Eclipse to generate my hashCode() method there is always the prime number 31 used: public int hashCode() { final int prime = 31; //… } References: Here is a good primer on Hashcode and article on … Read more
What’s a correct and good way to implement __hash__()? I am talking about the function that returns a hashcode that is then used to insert objects into hashtables aka dictionaries. As __hash__() returns an integer and is used for “binning” objects into hashtables I assume that the values of the returned integer should be uniformly … Read more
As per my understanding I think: It is perfectly legal for two objects to have the same hashcode. If two objects are equal (using the equals() method) then they have the same hashcode. If two objects are not equal then they cannot have the same hashcode Am I correct? Now if am correct, I have … Read more
When a class in Java doesn’t override hashCode(), printing an instance of this class gives a nice unique number. The Javadoc of Object says about hashCode(): As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. But when the class overrides hashCode(), how can I … Read more
How do we decide on the best implementation of hashCode() method for a collection (assuming that equals method has been overridden correctly) ? 20 Answers 20
Recently I read through this Developer Works Document. The document is all about defining hashCode() and equals() effectively and correctly, however I am not able to figure out why we need to override these two methods. How can I take the decision to implement these methods efficiently? 3Best Answer 31
This question’s answers are a community effort. Edit existing answers to improve this post. It is not currently accepting new answers or interactions. What issues / pitfalls must be considered when overriding equals and hashCode? 1Best Answer 11 The theory (for the language lawyers and the mathematically inclined): equals() (javadoc) must define an equivalence relation … Read more
A strict equality operator will tell you if two object types are equal. However, is there a way to tell if two objects are equal, much like the hash code value in Java? Stack Overflow question Is there any kind of hashCode function in JavaScript? is similar to this question, but requires a more academic … Read more
Is there any method to generate MD5 hash of a string in Java? 33 s 33
In .NET, the GetHashCode method is used in a lot of places throughout the .NET base class libraries. Implementing it properly is especially important to find items quickly in a collection or when determining equality. Is there a standard algorithm or best practice on how to implement GetHashCode for my custom classes so I don’t … Read more
