When Comparing Strings: Are `string.Equals()` and `==` Truly Interchangeable?

Are the

string.Equals() and == operators really interchangeable?

While both the string.Equals() and == operators are used to compare objects for equality, they behave differently.

For example, the variable s is a string containing "Category", and tvi.Header is the title of the WPF TreeViewItem, which also contains "Category". However, s == tvi.Header evaluates to false, while s.Equals(tvi.Header) evaluates to true.

This difference stems from two key differences:

1. Dynamic typing vs. static typing: Equals is polymorphic, which means that its implementation depends on the runtime type of the object. In this case, it will use the string implementation to compare the values ​​of two strings. == on the other hand is statically typed and will use the appropriate implementation based on the compile-time type of the object being compared (String and TreeViewItem.Header in this case). Since these types are different, == performs a reference comparison and returns false.
2. Null value handling: When Equals is called on a null object, a NullReferenceException exception is thrown, and == if both operands are null, the result is true. To avoid this problem, use object.Equals instead of Equals when dealing with potentially null objects.

To summarize, while the string.Equals() and == operators look similar, there are differences in types and null value handling. For accurate value comparisons, you should use string.Equals() when comparing string values, and watch out for null values ​​when using the == operator.

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