What's the Difference Between `string.Equals()` and the `==` Operator in C#?

C# String Comparison: Differences between string.Equals() and == Operators

String equality in C# often raises questions. Can the == operator and string.Equals() method really be used interchangeably? Let’s dive into their differences to clarify their usage.

Polymorphism and compile-time type determination

One major difference is their handling of polymorphism. string.Equals() The method is polymorphic, which means its implementation can be overridden in derived classes. This flexibility allows different types of objects to handle equality comparisons in a consistent manner.

In contrast, the == operator depends on the compile-time type of the operands. Therefore, if you compare two objects of different compile-time types (for example, a string and a WPF TreeViewItem.Header), it will perform a reference comparison, not a value comparison.

Null value handling

Another key difference is what happens when either operand is empty. If you try to call the string.Equals() method on an empty object, it will throw a NullReferenceException exception. However, the == operator returns true when comparing two null references.

To avoid this problem, you can use the object.Equals() method, which handles null values ​​gracefully. This method returns false if either operand is empty or true if both are empty or equal.

In summary, string.Equals() methods and == operators should not be used interchangeably. The former is polymorphic and provides value comparison; while the latter relies on compile-time type information and performs reference comparisons. Additionally, the object.Equals() method provides a consistent and null-safe way to compare objects for equality.

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