What is the difference between public, private, and protected?

 

In object-oriented programming, "public," "private," and "protected" are access modifiers that determine the visibility and accessibility of class members (fields and methods) from outside the class. These access modifiers control how other classes or code can interact with the members of a class. Here are the key differences between them, along with examples in Python:

1. Public:

   • Members declared as public are accessible from anywhere in the program, both from within the class itself and from outside the class.
   • Public members can be accessed directly using the object of the class or by referencing the class itself.
   • In many programming languages, if no access modifier is specified, members are considered public by default.

   python

class MyClass:
    def __init__(self):
        self.public_var = 10

    def public_method(self):
        return "This is a public method"

obj = MyClass()
print(obj.public_var)         # Accessing public_var
print(obj.public_method())    # Accessing public_method

Private:

• Members declared as private are only accessible from within the class itself. They are not directly accessible from outside the class.
• In many programming languages, you indicate a member as private by using a naming convention or access modifier (e.g., prefixing the member name with an underscore _).

python

class MyClass:
    def __init__(self):
        self._private_var = 20

    def _private_method(self):
        return "This is a private method"

obj = MyClass()

# Accessing _private_var directly is possible but considered a convention to indicate privacy
print(obj._private_var)

# Accessing _private_method directly is also possible but a convention
print(obj._private_method())

Protected:

• Members declared as protected are not directly accessible from outside the class, similar to private members. However, they can be accessed from derived classes (subclasses) that inherit from the class.
• In many programming languages, you indicate a member as protected by using a naming convention or access modifier (e.g., prefixing the member name with a single underscore _).

python

3. class MyBaseClass:
       def __init__(self):
           self._protected_var = 30
   
       def _protected_method(self):
           return "This is a protected method"
   
   
   class MyDerivedClass(MyBaseClass):
       def access_protected_member(self):
           return self._protected_var + self._protected_method()
   
   obj = MyDerivedClass()
   
   # Accessing _protected_var and _protected_method from a derived class
   result = obj.access_protected_member()
   print(result)
   

In the example above, _protected_var and _protected_method are indicated as protected, so they are not directly accessible from outside the classes. However, the MyDerivedClass class, which inherits from MyBaseClass, can access these protected members.

It's important to note that the specific syntax and conventions for access modifiers may vary between programming languages. While Python uses naming conventions (e.g., underscores) to indicate private and protected members, other languages may use keywords like private, protected, or public. The choice of access modifier depends on the language's design and conventions.