In object-oriented design, what is an interface?

In object-oriented design, what is an interface?

• A. A starting point with methods from which many classes can be built using those methods.
• B. A primitive data type to store numbers.
• C. A database schema for joining tables.
• D. A method of encrypting data.

Answer: (A)

An interface is a contract that specifies a set of methods that implementing classes must provide. It defines what operations are available without saying how they’re done, so different classes can offer their own implementations but still be used interchangeably whenever they share the same interface. This enables polymorphism: you can write code that depends on the interface rather than on a concrete class, so any class that implements the interface can be used in place of another. The option described captures this idea as a starting point—defining the methods that concrete classes will implement to form a family of related behaviors. It isn’t a primitive data type, a database schema, or a method of encrypting data, which are roles handled by other language features.

An interface is a contract that specifies a set of methods that implementing classes must provide. It defines what operations are available without saying how they’re done, so different classes can offer their own implementations but still be used interchangeably whenever they share the same interface. This enables polymorphism: you can write code that depends on the interface rather than on a concrete class, so any class that implements the interface can be used in place of another. The option described captures this idea as a starting point—defining the methods that concrete classes will implement to form a family of related behaviors. It isn’t a primitive data type, a database schema, or a method of encrypting data, which are roles handled by other language features.