Understanding the Equals and HashCode Contract in Java

source : javatpoint.com

In the world of Java programming, the equals and hashCode methods play a crucial role in object comparison and hashing. They are foundational elements of the Java language, integral for implementing data structures like HashMaps and HashSets effectively. However, their usage and implementation are often misunderstood, leading to bugs and inefficiencies in code. In this article, we’ll delve into the equals and hashCode contract in Java, explaining each concept thoroughly with clear examples.

Equals Method:
The equals method in Java is used to compare the equality of two objects. It’s defined in the Object class and can be overridden in custom classes to provide meaningful comparison logic. The general contract for the equals method is as follows:

Reflexive: For any non-null reference value x, x.equals(x) should return true.

Symmetric: For any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.

Transitive: For any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.

Consistent: For any non-null reference values x and y, multiple invocations of x.equals(y) should consistently return the same…