What's the Difference Between `==` and `Equals()`/`equals()` for Comparing Objects in Java and C#?

In-depth discussion of object comparison in Java and C#: the difference between == and Equals/equals

In programming, determining whether two values ​​are equal is a basic operation. Both Java and C# provide two operators for this purpose: == and Equals/equals. However, the results of their operation may vary depending on the context.

Identity comparison (==)

The

== operator checks whether two references point to the same memory location, indicating reference equality. Essentially, it compares the addresses of objects, not their contents. The behavior is consistent in both Java and C#.

Equals/equals

On the other hand, the Equals/equals method provides greater flexibility. In Java, Equals checks whether values ​​are equal, comparing the contents of objects. However, this behavior is virtual, which means it can be overridden in derived classes. If not overridden, Equals defaults to identity comparison.

In C#, the behavior of == depends on the compile-time type of the object. For reference types, it performs reference equality, similar to Java. However, user-defined operators may be used if they are overloaded, allowing value equality comparisons.

Runtime context

Importantly, Equals/equals compares the runtime type of the object, not the compile-time type. This means that even if two variables are declared as the same type at compile time, their runtime types may be different, which may lead to different comparison results.

null value

It should be noted that in Java and C#, using Equals/equals on a null reference will throw an exception.

Summary

The key difference between == and Equals/equals is that == checks references for equality, while Equals/equals compares values. In Java, Equals overrides the default identity comparison in Object, while in C# it is used unless an overload exists. Understanding these differences is critical to writing robust code that accurately compares values.

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