Interface vs. Class — What's the Difference?
By Maham Liaqat & Fiza Rafique — Updated on May 8, 2024
An interface defines a set of methods that a class must implement, providing a contract without implementation, whereas a class is a blueprint that defines both the structure (fields) and behavior (methods) of objects, including implementation.
Difference Between Interface and Class
Table of Contents
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Key Differences
An interface defines a collection of abstract methods that a class must implement, whereas a class contains concrete implementations of fields and methods.
An interface enables multiple inheritance by allowing a class to implement multiple interfaces, while a class can inherit directly from only one superclass.
An interface cannot contain any field implementations or instance methods but can include default or static methods in some languages, whereas a class can encapsulate state through instance variables and methods.
An interface emphasizes a contract for behavior that various classes can implement differently, whereas a class defines behavior and structure directly, providing complete or partial implementation.
An interface is commonly used in large-scale system design to promote decoupling and modularity, while a class provides concrete functionality that makes up the building blocks of an application.
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Comparison Chart
Implementation
No concrete implementation
Provides full implementation
Fields
No instance fields (only constants allowed)
Instance fields are common
Inheritance
Allows multiple inheritance
Single inheritance (extends only one)
Abstraction
Fully abstract methods
Can be abstract or concrete
Purpose
Contract for implementation
Blueprint with actual implementation
Compare with Definitions
Interface
A set of method signatures that classes must implement.
The Runnable interface in Java defines the run method.
Class
Contains method implementations.
The add method in ArrayList adds an element to the array.
Interface
A class can implement multiple interfaces.
A class can implement both Serializable and Cloneable interfaces.
Class
Allows creating objects.
Car myCar = new Car(); creates a new instance of the Car class.
Interface
Some languages allow these methods in interfaces.
Java allows default methods to provide base implementation in interfaces.
Class
A structure defining both fields and methods.
The ArrayList class provides a dynamic array implementation.
Interface
Commonly used across many programming languages.
Both Java and C# support interfaces for abstraction.
Class
Organizes fields and methods into logical units.
A Person class encapsulates name and age fields with methods.
Interface
Method declarations without implementation.
Public void draw(); in an interface requires implementation in a class.
Class
Can inherit from a single superclass.
A Car class can inherit from a Vehicle superclass.
Interface
A surface forming a common boundary between adjacent regions, bodies, substances, or phases.
Class
A set, collection, group, or configuration containing members regarded as having certain attributes or traits in common; a kind or category.
Interface
A point at which independent systems or diverse groups interact
"the interface between crime and politics where much of our reality is to be found" (Jack Kroll).
Class
A grade of mail
A package sent third class.
Interface
A system of interaction or communication between a computer and another entity such as a printer, another computer, a network, or a human user.
Class
A quality of accommodation on public transport
Tourist class.
Interface
A device, such as a cable, network card, monitor, or keyboard, that enables interaction or communication between a computer and another entity.
Class
A social stratum whose members share certain economic, social, or cultural characteristics
The lower-income classes.
Interface
The layout or design of the interactive elements of a computer program, an online service, or an electronic device.
Class
Social rank or caste, especially high rank.
Interface
To join by means of an interface.
Class
(Informal)Elegance of style, taste, and manner
An actor with class.
Interface
To serve as an interface for.
Class
A group of students who are taught together, usually at a regularly scheduled time and in the same subject.
Interface
To serve as an interface or become interfaced.
Class
The period during which such a group meets
Had to stay after class.
Interface
Usage Problem To interact or coordinate smoothly
"Theatergoers were lured out of their seats and interfaced with the scenery" (New York Times).
Class
The subject material taught to or studied by such a group
Found the math class challenging.
Interface
The point of interconnection or contact between entities.
Public relations firms often serve as the interface between a company and the press.
Class
A group of students or alumni who have the same year of graduation.
Interface
A thin layer or boundary between different substances or two phases of a single substance.
If water and oil are mixed together, they tend to separate, and at equilibrium they are in different strata with an oil-water interface in between.
The surface of a lake is a water-air interface.
Class
(Biology)A taxonomic category ranking below a phylum or division and above an order.
Interface
(computing) The point of interconnection between systems or subsystems.
The data is sent over the air interface to the remote system.
Class
(Statistics)An interval in a frequency distribution.
Interface
(computing) The connection between a user and a machine.
The options are selected via the user interface.
Class
(Linguistics)A group of words belonging to the same grammatical category that share a particular set of morphological properties, such as a set of inflections.
Interface
The connection between parts of software; also the public or published sections of an object or module,
This interface is implemented by several Java classes.
Traits are somewhat between an interface and a mixin, as an interface contains only method signatures, while a trait includes also the full method definitions; on the other side mixins include method definitions, but they can also carry state through attributes, while traits usually don't.
Class
(Mathematics)A collection of sets whose members share a specified property.
Interface
In object-oriented programming, a piece of code defining a set of operations that other code must implement.
The Audio and Video classes both implement the IPlayable interface.
Class
To arrange, group, or rate according to qualities or characteristics; assign to a class; classify.
Interface
(biochemistry) The internal surface of a coiled protein (compare exoface).
Class
(countable) A group, collection, category or set sharing characteristics or attributes.
The new Ford Fiesta is set to be best in the 'small family' class.
That is one class-A heifer you got there, sonny.
Often used to imply membership of a large class.
This word has a whole class of metaphoric extensions.
Interface
(transitive) To construct an interface for.
Class
A social grouping, based on job, wealth, etc. In Britain, society is commonly split into three main classes: upper class, middle class and working class.
Interface
(ambitransitive) To connect through an interface.
Class
(uncountable) The division of society into classes.
Jane Austen's works deal with class in 18th-century England.
Interface
(intransitive) To serve as an interface.
Class
(uncountable) Admirable behavior; elegance.
Apologizing for losing your temper, even though you were badly provoked, showed real class.
Interface
To meet for discussion.
Let's interface on Wednesday.
Class
A group of students in a regularly scheduled meeting with a teacher.
The class was noisy, but the teacher was able to get their attention with a story.
Interface
A surface forming a common boundary between two things, especially between two fluids.
Class
A series of lessons covering a single subject.
I took the cooking class for enjoyment, but I also learned a lot.
Interface
Hardware that links one device with another (especially a computer).
Class
(countable) A group of students who commenced or completed their education during a particular year. A school class.
The class of 1982 was particularly noteworthy.
Interface
That part of a computer program which controls the way a program interacts with a user; the manner of inputting and outputting of data, and the way information is presented on a computer monitor; also called user interface; as, a graphical user interface; a character-based interface.
Class
(countable) A category of seats in an airplane, train or other means of mass transportation.
I used to fly business class, but now my company can only afford economy.
Interface
(chemistry) a surface forming a common boundary between two things (two objects or liquids or chemical phases)
Class
A rank in the classification of organisms, below phylum and above order; a taxon of that rank.
Magnolias belong to the class Magnoliopsida.
Interface
(computer science) a program that controls a display for the user (usually on a computer monitor) and that allows the user to interact with the system
Class
Best of its kind.
It is the class of Italian bottled waters.
Interface
The overlap where two theories or phenomena affect each other or have links with each other;
The interface between chemistry and biology
Class
(statistics) A grouping of data values in an interval, often used for computation of a frequency distribution.
Interface
(computer science) computer circuit consisting of the hardware and associated circuitry that links one device with another (especially a computer and a hard disk drive or other peripherals)
Class
(set theory) A collection of sets definable by a shared property.
The class of all sets is not a set.
Every set is a class, but classes are not generally sets. A class that is not a set is called a proper class.
Class
(military) A group of people subject to be conscripted in the same military draft, or more narrowly those persons actually conscripted in a particular draft.
Class
A set of objects having the same behavior (but typically differing in state), or a template defining such a set in terms of its common properties, functions, etc.
An abstract base class
Class
One of the sections into which a Methodist church or congregation is divided, supervised by a class leader.
Class
(transitive) To assign to a class; to classify.
I would class this with most of the other mediocre works of the period.
Class
(intransitive) To be grouped or classed.
Class
(transitive) To divide into classes, as students; to form into, or place in, a class or classes.
Class
Great; fabulous
Class
A group of individuals ranked together as possessing common characteristics; as, the different classes of society; the educated class; the lower classes.
Class
A number of students in a school or college, of the same standing, or pursuing the same studies.
Class
A comprehensive division of animate or inanimate objects, grouped together on account of their common characteristics, in any classification in natural science, and subdivided into orders, families, tribes, genera, etc.
Class
A set; a kind or description, species or variety.
She had lost one class energies.
Class
One of the sections into which a church or congregation is divided, and which is under the supervision of a class leader.
Class
One session of formal instruction in which one or more teachers instruct a group on some subject. The class may be one of a course of classes, or a single special session.
Class
A high degree of elegance, in dress or behavior; the quality of bearing oneself with dignity, grace, and social adeptness.
Class
To arrange in classes; to classify or refer to some class; as, to class words or passages.
Class
To divide into classes, as students; to form into, or place in, a class or classes.
Class
To be grouped or classed.
The genus or family under which it classes.
Class
Exhibiting refinement and high character; as, a class act. Opposite of low-class
Class
People having the same social or economic status;
The working class
An emerging professional class
Class
A body of students who are taught together;
Early morning classes are always sleepy
Class
Education imparted in a series of lessons or class meetings;
He took a course in basket weaving
Flirting is not unknown in college classes
Class
A collection of things sharing a common attribute;
There are two classes of detergents
Class
A body of students who graduate together;
The class of '97
She was in my year at Hoehandle High
Class
A league ranked by quality;
He played baseball in class D for two years
Princeton is in the NCAA Division 1-AA
Class
Elegance in dress or behavior;
She has a lot of class
Class
(biology) a taxonomic group containing one or more orders
Class
Arrange or order by classes or categories;
How would you classify these pottery shards--are they prehistoric?
Common Curiosities
What is the main difference between an interface and a class?
An interface provides a set of method signatures, while a class provides the actual implementation of those methods.
Can a class inherit from multiple classes?
In most programming languages, a class can inherit from only one superclass.
Can an interface have concrete methods?
In some languages like Java, interfaces can have default or static methods, which are concrete.
Why would I use an interface instead of a class directly?
Interfaces offer flexibility in changing implementations and promote modular code design.
Can a class implement multiple interfaces?
Yes, a class can implement multiple interfaces, allowing for flexible design.
Can interfaces contain fields?
Interfaces can only contain constants, not instance fields.
Can a class implement an interface partially?
No, a class must fully implement all methods in the interfaces it declares.
Can a class implement an interface and extend a superclass simultaneously?
Yes, a class can implement one or more interfaces while extending a single superclass.
What are abstract classes, and how are they different from interfaces?
Abstract classes can provide partial implementation and can contain fields, unlike interfaces.
Is it necessary to use interfaces?
While not mandatory, interfaces can help in designing extensible and testable software.
How does an interface promote decoupling?
Interfaces allow changing the implementation behind the interface without affecting other parts of the program.
How does a class differ from a struct or a record?
Classes often support inheritance and polymorphism, while structs/records typically focus on data storage.
Can a class extend multiple interfaces?
A class can implement multiple interfaces, gaining their behavior contracts.
Can an interface extend another interface?
Yes, an interface can extend other interfaces to inherit their method signatures.
Are interfaces and abstract classes the same in all programming languages?
No, different languages have varying rules and features for abstract classes and interfaces.
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Written by
Maham Liaqat
Co-written by
Fiza RafiqueFiza Rafique is a skilled content writer at AskDifference.com, where she meticulously refines and enhances written pieces. Drawing from her vast editorial expertise, Fiza ensures clarity, accuracy, and precision in every article. Passionate about language, she continually seeks to elevate the quality of content for readers worldwide.
