Why is hashcode needed

Hi Dhara, Please check line 70 in first code and line 81 in second code snippet, i have added object m4. Thanks, Jitendra Zaa. Can you please correct it. That is the reason i have used code like this. Yes got your explanation now.. Pjoshi : Jitendra Zaa is absolutly correct, although the m4 object not been added in the map, but m4 is the exact copy of m2 and m2 is getting used here as a KEY, so it will return m2 object value.

Please correct me if i am wrong. Thanks K. Perfect demonstration of hashcode and equals and it cleared most of my doubts. Thanx u v. JVM assigns unique hashcode value to each object when they are created in memory. It is just a perfect explanation with perfect example.. It cleared all my doubts.. Thanks for the explanation.. So is this explanation meaning , logically equals objects should be treated as same key in hash map and they should be stored in the same bucket in hashtable.

Hi Jitendra, just one question.. I debugged the program and saw after putting values in map it goes there, but why? Thanks in advance. The article is very helpful. Though the flow of call between equal ,hash code and the main is not clear.

It will be very helpful ,If anyone explain the flow. Here we are not adding the m4 as key to Hashmap,But still we can able to get that from Hashmap. Can pls explain it clearly. Hi Jitendra, Thanks,My questions is that Object class provides default implemtation then why we should override these methods what is the actual difference between Objects equal method and override custom class equal method?

In Object class. In String class and all Wrapper classes,. But everybody starts explaining how its being used in hashtables and hashmaps. Thanks Jitendra for this blog.

Jitendra Zaa is absolutly correct, although the m4 object not been added in the map, but m4 is the exact copy of m2 and m2 is getting used here as a KEY, so it will return m2 object value. How Do Annotations Work in Java? How do I use the ternary operator in Java? What is instanceof keyword in Java? How ClassLoader Works in Java? What are fail-safe and fail-fast Iterators in Java What are method references?

Does garbage collection guarantee that a program will not run out of memory? How setting an Object to null help Garbage Collection? How do objects become eligible for garbage collection? How to calculate date difference in Java Difference between Path and Classpath Is Java "pass-by-reference" or "pass-by-value"? Difference between static and nonstatic methods java Why Java does not support pointers?

What is package in Java? What are wrapper classes? What is singleton class in Java? Can a top level class be private or protected in java Are Polymorphism , Overloading and Overriding similar concepts? Why can't a Java class be declared as static? Difference between Abstract class and Interface in Java Why does Java not support operator overloading?

How to generate random integers within a specific range in Java What's the meaning of System. Now any time an element with the same hash code is inserted into the set, it will just replace alex1. However, since alex2 has a different hash code, it will be stored in a separate bucket and will be considered a totally different object.

Now when HashSet searches for an element inside it, it first generates the element's hash code and looks for a bucket which corresponds to this hash code. Here comes the importance of overriding hashcode , so let's override it in Student and set it to be equal to the ID so that students who have the same ID are stored in the same bucket:.

See the magic of hashcode! The two elements are now considered as equal and stored in the same memory bucket, so any time you call contains and pass a student object holding the same hash code, the set will be able to find the element. The same is applied for HashMap, HashTable , or any data structure that uses a hashing mechanism for storing elements.

In order to achieve a fully working custom equality mechanism, it is mandatory to override hashcode each time you override equals. Follow the tips below and you'll never have leaks in your custom equality mechanism:. See the original article here. Thanks for visiting DZone today,. Edit Profile. Sign Out View Profile. Over 2 million developers have joined DZone. Working With hashcode and equals. Need to implement your own custom equality-checking mechanism? Here are some tips for when you need to override hashcode and equals.

Like Join the DZone community and get the full member experience. Join For Free. Method Definition and Default Implementation equals Object obj : a method provided by java.