Agreement Between Hashcode and Equals
When it comes to programming, Hashcode and Equals are two methods that are commonly used to compare objects in Java. While both methods are essential, they have some subtle differences that may not be apparent to new programmers. Understanding the agreement between Hashcode and Equals is crucial in ensuring your code is efficient, correct, and easy to maintain.
What is Hashcode?
In Java, Hashcode is a method that returns a unique integer for an object. The integer is generated using an algorithm that converts an object`s data into a 32-bit number. This number is used to place the object in a hash table, which is a data structure that allows for fast access to items.
What is Equals?
Equals, on the other hand, is a method that checks if two objects are equal. The method is used to test if two objects have the same data and state. If two objects are equal, the Equals method returns true. If not, it returns false.
The Hashcode and Equals methods have to work together correctly for your code to function correctly. The agreement between the Hashcode and Equals methods states that if two objects are equal, then their hash codes must be equal too. The reverse is not necessarily true. Two objects with the same Hashcode are not guaranteed to be equal.
This agreement is vital because it ensures that objects are correctly placed in hash tables. A hash table will store each object in a specific slot, and the slot is determined by the object`s hash code. If two objects with different data have the same hash code, they will end up in the same slot. This situation causes a collision, and the hash table will have to use additional logic to determine which object is which.
Therefore, when you override the Equals method, you should also override the Hashcode method to ensure the agreement between the two is maintained. The default implementation of Hashcode returns a unique number for every object, even if the objects have the same data. Therefore, if you override the Equals method and not the Hashcode method, you will end up with objects that are considered equal but have different hash codes.
In summary, understanding the agreement between Hashcode and Equals is crucial in ensuring your code is efficient, correct, and easy to maintain. When you override the Equals method, you should also override the Hashcode method to ensure the two methods work together correctly. This will help your code avoid collisions and correctly store and retrieve objects from hash tables.