How does java hashcode

The hashcode method of Java is needed to be overridden in every class, which helps to override the methods like equal. During the time of executing the application, If the hashcode method is invoked more than one time on the particular same object, then hashcode will return the same integer value consistently.

This is an example of converting a blog link and some text into hash code conversion. Before this, save the program file in the name of StringExample1.

Then the main function is created to enter the java program code. Then again, a textprint1 variable is created with some string text. Then hashcode function is made to convert the profitloops. Likewise, for the other string text too, the string will be converted into hash code. Then closing of the parenthesis for the correct syntax purpose. Check out the output below so that you will get an idea of how the hash code is turned.

A hash function is just a mathematical function. Here it means only that we have some data and a certain rule that maps the data into a set of characters code. For example, it could be a hexadecimal cipher. We have some data of any size at the input, and apply a hash function to it. At the output, we get a fixed-size data, say, 32 characters. Usually, that kind of function converts a big piece of data into a small integer value.

The result of this function work is called a hash code. Hash functions are widely used in cryptography, and some other areas too. Hash functions can be different, but they all have certain properties: A particular object has a particular hash code.

If two objects are equal, their hash codes are the same. The reverse is not true. If two objects are at same memory location the same object referred by two reference variable then hashcode number for both will be same but if two objects reside at different memory location then hashcode number for both object will be different.

You probably asked the question because you need to override the method. But, when to override it? Default implementation of hashCode method returns hashcode number unique identity of object based on the address of the object.

But if my application requires to uniquely identify the objects based on some different parameter rather than address of the object , then I should override hashCode method and should give implementation as per the requirement.

For more, check out this Java hashcode example. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Ask Question. Asked 11 years, 10 months ago. Active 2 years, 3 months ago. Viewed 31k times.

Improve this question. Luke Francl Hellnar Hellnar Add a comment. Active Oldest Votes. Now, regarding the how it works, this answer from Tom Hawtin does a great job at explaining it: Many people will claim that Object.

The whole answer is actually worth the read. Which is more expensive and requires coordination. Lines L to L deal with finding the header and checking for a cached identity hash. From L it needs to bite the bullet:. At this point, if the id. I wrote a simple JMH harness to verify those conclusions. The benchmark source does something equivalent to this:. One configuration withIdHash synchronizes on an object that uses the identity hash, so we expect that biased locking will be disabled as soon as hashCode is invoked.

A second configuration withoutIdHash implements a custom hash code so biased locking should not be disabled. When two threads contend for the lock, biased locking is disabled anyway so there is no significative difference between both hash methods.

The hash method no longer has any impact and withoutIdHash loses its advantage. Whatever is not wild speculation and my weak reasoning trying to make sense of the JVM sources, comes from stitching together various sources about layout, biased locking, etc. The main ones are below:. To get notifications for new posts, subscribe to the RSS feed or follow me on Twitter. Here is the log of older posts.

A trivial mystery Last week at work I submitted a trivial change to a class, an implementation of toString so logs would be meaningful.

Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer. A randomly generated number.