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

Deeply explore the differences between == and Equals()/equals() in Java and C#

In programming, the equality operator is crucial in value comparison. A common question is the difference between the == operator and the Equals or equals method.

For reference types (objects) in Java and C#, the == operator checks whether two variables refer to the same object, that is, reference equality. Instead, Equals or equals calls a virtual method defined in the Object class, which typically validates the identity but can be overridden by a specific type, thereby implementing a value equality check.

Java implementation

In Java, == always checks reference equality, which means it determines whether two references point to the same object. There are no user-defined operator overloading in Java, so the behavior remains the same.

Flexibility of C#

C# provides greater flexibility in comparison. ==Reference equality is enforced by default. However, if an overload exists for a variable of a specific compile-time type (for example, a string), that overload will be implemented. This overload can define its own behavior, typically implementing value equality, where two different references can have the same value.

Equals and equals

In Java and C#, a.Equals(b) or a.equals(b) calls a virtual Object or Equals method inherited from the equals class. This method checks for identity by default. However, it can be overridden in specific types to enable custom value comparisons, depending on the runtime type of the object being referenced.

Handling null values

Note that attempting to use Equals or equals with a null reference will result in NullReferenceException or NullPointerException.

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