Software Engineering basics - Note on Object Interface Specification
An object interface specification defines how objects in an object-oriented system interact with one another. It describes the services (operations or methods) that an object provides to the outside world, without revealing its internal implementation details.
In other words, it defines what an object does, not how it does it.
Key Points:
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Definition:
An object interface is a contract between the object and its clients, specifying the set of operations that can be invoked and the types of data exchanged. -
Purpose:
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To ensure clear communication between objects.
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To promote encapsulation by hiding implementation details.
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To enable modularity, reusability, and maintainability.
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Contents of an Interface Specification:
An interface specification usually includes:-
Object name or class name
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Operation names (methods the object can perform)
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Parameters (input and output types for each operation)
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Preconditions (conditions that must be true before operation execution)
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Postconditions (conditions that will be true after operation execution)
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Exceptions or errors (what happens when operations fail)
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Example:
Consider a BankAccount class.
Interface Specification:
| Operation | Description | Input | Output | Precondition | Postcondition |
|---|---|---|---|---|---|
deposit(amount) |
Adds money to the account | amount: float |
— | amount > 0 |
Balance increased by amount |
withdraw(amount) |
Withdraws money from the account | amount: float |
— | amount > 0 and balance ≥ amount |
Balance decreased by amount |
getBalance() |
Returns current balance | — | balance: float |
— | No change to object state |
Advantages:
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Promotes information hiding and abstraction.
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Allows independent development of different system components.
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Simplifies testing and maintenance.
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Facilitates reuse of objects in other systems.
In Summary:
Object interface specification clearly defines how other objects or modules can interact with a given object. By specifying operations, inputs, outputs, and constraints, it acts as a formal description of the object’s external behavior—ensuring that systems built using object-oriented principles remain modular, reliable, and easy to evolve.
