Access privileges of private members [duplicate]

This question already has answers here: Closed 11 years ago.

We cannot access a private variable of a class from an object, which is created outside the class, but it is possible to access when the same object is created inside the class, itself. why??

class Program { private int i;

public void method1()
{            
    Program p = new Program();
    p.i = 5; 开发者_StackOverflow社区       // OK when accessed within the class
}

}

class AnotherClass {

void method2()
{
    Program p = new Program();
    p.i = 5; //error because private variables cannot be accessed with an object which is created out side the class
}

}

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see this Access Modifiers

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It's a design consideration of OO that allows classes to only expose the functionality that they wish to be re-used by other classes (as public / protected methods) and to keep some functionality internal to the class and not re-usable.