String.Equals() vs. == in C#: Are They Truly Equivalent?

C# string comparison: the difference between string.Equals() and ==

In C#, the string.Equals() method and the == operator look very similar, but there are subtle differences between them that can lead to unexpected results.

Polymorphism and runtime types

A key difference is polymorphism. Equals() is a polymorphic method, which means its implementation can be overridden based on the runtime type of the target object. In contrast, the implementation of == is determined solely by the compile-time types of the operands. This difference becomes apparent when comparing objects of different types, because the Equals() implementation of the target object's class will be called, and == will perform a reference comparison based on the compile-time type.

Null values ​​and exceptions

Another difference is the way null values ​​are handled. If Equals() is called on a null object, it will throw a NullReferenceException exception, while == will simply return false. This can become a problem when comparing objects that may be null. To avoid this problem, you can use the object.Equals() method, which checks for null values ​​before calling Equals().

Example

Consider the following code:

<code class="language-csharp">object x = new StringBuilder("hello").ToString();
object y = new StringBuilder("hello").ToString();

// Equals() 将比较值，考虑运行时类型
if (x.Equals(y)) // True

// == 将执行引用比较，而不管运行时类型
if (x == y) // False</code>

In this example, x correctly compares the values ​​of y and Equals() even though x and y are different types of objects. However, == performs a reference comparison and returns false because they are not instances of the same string object.

Conclusion

While Equals() and == look similar, their behavior differs in key ways. Understanding these differences is crucial to avoid unexpected string comparisons and ensure proper object equality checking.

The above is the detailed content of String.Equals() vs. == in C#: Are They Truly Equivalent?. For more information, please follow other related articles on the PHP Chinese website!