I am trying to generate a HashSet containing unique Employee instances. Uniqueness should be established based on the object properties. The problem is that I end up with having duplicates. Note that Employee class is provided by a framework, and it’s not possible to provide custom implementations for e…
Tag: hashcode
Which choice is better for generating equals() and hashCode() methods in Hibernate?
I create equals() and hashCode() methods in each Hibernate entity (if there is no inheritance) in my Java app. However, I am a little bit confused and wanted to be sure if I define it properly. Could you please clarify the following issues? In IntelliJ, when I use the “Generate” feature (via Alt +…
How can UserDefined class be a key of hashmap if hashCode() & equals() return same value
I am trying to implement HashMap with UserDefined class as Key, i am successfull even when I implement both hashCode() (returns 0 for every object) & equals() (returns false for every object). My Code output:- Can anyone let me know the reason how it’s working Answer This is happening because equals…
Hashcode value for Map Entry
As per javadocs hashcode for a map.entry is defined as : Plz confirm, if a bitwise XOR operator is used for calculating the hashcode value for a map entry? Answer Yes, it indeed is a bitwise XOR operator. I tried & got the same result for both the hashcode() method & by using ^ operator.
How to create a HashMap with two keys (Key-Pair, Value)?
I have a 2D array of Integers. I want them to be put into a HashMap. But I want to access the elements from the HashMap based on Array Index. Something like: For A[2][5], map.get(2,5) which returns a value associated with that key. But how do I create a hashMap with a pair of keys? Or in general, multiple key…
How could a LinkedHashMap fail to find an entry produced by an iterator?
Under what circumstances given a correct implementation of hashCode and equals() can the following code return false? Answer Most likely scenario I can think of would be even though hashCode is “deterministic”, it may be based on mutable fields. If you change the fields used to compute hashCode af…
is there hash code / Heap address for primitive types in Java?
I was trying to find some approximization to address on heap , and you guys gave me the function System.IdentityHashCode(Object). The problem is – this function doesn’t fit for primitive types. I’ll explain why. I’m given as input Java compiled program – class file. My goal is to…
Why can hashCode() return the same value for different objects in Java?
A quote from the book I’m reading Head First Java: The point is that hashcodes can be the same without necessarily guaranteeing that the objects are equal, because the “hashing algorithm” used in the hashCode() method might happen to return the same value for multiple objects. Why might the …
Why doesn’t String’s hashCode() cache 0?
I noticed in the Java 6 source code for String that hashCode only caches values other than 0. The difference in performance is exhibited by the following snippet: Running this in ideone.com gives the following output: So my questions are: Why doesn’t String’s hashCode() cache 0? What is the probab…
How should equals and hashcode be implemented when using JPA and Hibernate
How should model class’s equals and hashcode be implemented in Hibernate? What are the common pitfalls? Is the default implementation good enough for most cases? Is there any sense to use business keys? It seems to me that it’s pretty hard to get it right to work in every situation, when lazy fetc…