Why Can Objects of the Same Class Access Each Other's Private Fields?

Accessing Private Fields in the Same Class: A Puzzling Design Choice

The concept of private fields in object-oriented programming aims to restrict access to specific members of an object to only the object's internal methods. However, an anomaly arises in the scenario where two instances of the same class can access each other's private fields. This raises the question: Why was object-oriented programming designed to allow class-level rather than object-level protection for private members?

Consider the following code snippet:

class Person {
    private BankAccount account;

    Person(BankAccount account) {
        this.account = account;
    }

    public Person someMethod(Person person) {
        // Accessing private field directly
        BankAccount a = person.account;
    }
}

In this code, the someMethod function of the Person class has direct access to the account field of another instance of the same class. This contradicts the principle of encapsulation that underlies object-oriented programming.

Delving into the seemingly counterintuitive design choice, some insights emerge. One plausible explanation is derived from the principle of encapsulation itself. Private visibility aims to protect the internal state of an object from external modifications. However, when two instances of the same class interact, both instances are assumed to be privy to the internal workings of the class. This level of trust eliminates the need for object-level access restrictions.

Another reason lies in the nature of class-level access. The private access modifier, as the name suggests, grants access only within the class. This implies that any method or constructor within the class has unrestricted access to the private members. Therefore, when one object references another object of the same class, the class-level access applies to both objects, providing access to the private fields.

In conclusion, while the ability to access private fields of other objects in the same class may seem paradoxical, it stems from the underlying principles of encapsulation and class-level access. This design choice enables objects to interact freely within the confines of their class, preserving the integrity of the internal state while facilitating efficient communication.

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