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Basic Classes and Objects
Public vs. Private

At this point we have built fields to associate data with a class and properties to control the getting and setting of each field. As it is now, any code outside of the Forest class can “sneak past” our properties by directly accessing the field:

f.Age = 32; // using property f.age = -1; // using field

The second line avoids the property’s validation by directly accessing the field. We can fix this by using the access modifiers public and private:

  • public — a public member can be accessed by any class
  • private — a private member can only be accessed by code in the same class

For simplicity, we’ve been adding public to every member so far. That allows code to access the members from the Main() method, which doesn’t belong to the Forest class. When we switch a field from public to private it will no longer be accessible from Main(), although code inside the Forest class — like properties — can still access it.

Access modifiers can be applied to all members of a class, including fields, properties, and the rest of the members covered in this lesson.

Remember encapsulation? public and private are necessary to encapsulate our classes. Think of it like “defensive coding”: you are protecting the inner mechanisms of a class with private so that other code can’t break your class. You only expose what you want to be public.

For example, since a class’ properties define how other programs get and set its fields, it’s good practice to make fields private and properties public.

C# encourages encapsulation by defaulting class members to private and classes to public.

Instructions

1.

Currently the biome field and Biome property are public. In Program.cs, the field is directly accessed and set to "Desert", an invalid value.

Run the code to see that “Desert” is the field’s value.

2.

By directly accessing the public biome field the code skipped the validation. Let’s prevent that by setting the biome field to private in Forest.cs.

When you run the code, you should see the error:

error CS0122: 'Forest.biome' is inaccessible due to its protection level

That means C# has prevented us from accessing a private field (which is good).

3.

Address the error by changing the code in Program.cs: use the property (Biome) instead of the field (biome). You’ll need to change code in two places in the file.

What is printed to the console now?

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