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String, The Exception
Strings Can Look Like Values

String, or string, is a class that represents text. Technically its value is stored as a collection of char objects.

Since it is a class, it is a reference type. In some cases its behavior looks like a value type:

  • A string reference will always point to the original object, so “modifying” one reference to a string will not affect other references
  • Comparing strings with the equality operator (==) performs a value, not referential, comparison

Here’s are two examples of the first behavior (modifying one reference doesn’t affect the others):

// Example 1 string dog = "chihuahua"; string tinyDog = dog; dog = "dalmation"; Console.WriteLine(dog); // Output: "dalmation" Console.WriteLine(tinyDog); // Output: "chihuahua" // Example 2 string s1 = "Hello "; string s2 = s1; s1 += "World"; System.Console.WriteLine(s1); // Output: "Hello World" System.Console.WriteLine(s2); // Output: "Hello"

The can be explained by the fact that strings are immutable: they cannot be changed after they are created. Anything that appears to modify a string actually returns a new string object.

Here’s an example of the second behavior (value-like comparisons):

string s = "hello"; string t = "hello"; // b is true bool b = (s == t);

Typically we want to compare strings by value, so this makes it easier to write in code and it also gives the C# compiler flexibility in how it implements the program (it doesn’t have to worry about where the actual string value is stored).

Instructions

1.

Create two string variables with the same value: "immutable".

2.

Compare the two variables using == and print the result.

Why does this return true?

3.

Now repeat the process with two Object variables:

  • Construct two new Object instances and store them in two new variables
  • Compare them with ==

Make sure to call new Object() twice. Why are the results different?

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