Think of interfaces as a contract, one where classes that implement an interface agree to provide implementations for all objects defined by that interface. Interfaces cannot contain any implementations, and their names are generally prefixed with "I" to distinguish them from other C objects. We create interfaces using the interface keyword:. Classes and structs can then implement an interface and define the behavior of the interface's methods:.
Note that the implementing class must provide a definition for all methods defined on the interface. If it does not, we get a compilation error:.
However, because of polymorphism , we can use interfaces as the type of a variable, and the resulting object will only have the members of the interface be usable:.
Any class or struct which implements an interface must implement all methods and properties from any of that interface's inherited interfaces:. Likewise, a single class can implement multiple interfaces, and must define behavior for all methods and properties from those interfaces:. In short, interfaces allow us to define a set of properties and method definitions which any implementing classes must provide their own implementations for.
Abstract classes serve a slightly different purpose than interfaces. An abstract class is a "partially implemented" class which other classes can inherit from, but if they do, they must provide their own implementations for any method in the abstract class that is not already implemented. An abstract class is defined using the abstract keyword. This keyword tells us that the object being modified has a missing or incomplete implementation, and that classes which inherit from the abstract class must provide the missing pieces of the implementation.
Methods in an abstract class may also be declared abstract ; these methods will not have an implementation. However, abstract classes can also contain methods with an implementation. Methods which are declared as abstract must be implemented in any derived class that inherits from the abstract class. If our derived class does not implement all the abstract members, we get a compilation error. An instance of the derived class may call methods defined in the derived class as well as any non-abstract methods in the base class:.
Properties can also be declared abstract, and derived classes can implement them using the override keyword:. Also, like an interface, an abstract class can be used as a variable type due to polymorphism.
A class or struct can implement multiple interfaces, but a class can only inherit from a single class. Interfaces can contain instance methods, properties, events, indexers, or any combination of those four member types.
Interfaces may contain static constructors, fields, constants, or operators. An interface can't contain instance fields, instance constructors, or finalizers. Interface members are public by default, and you can explicitly specify accessibility modifiers, such as public , protected , internal , private , protected internal , or private protected.
A private member must have a default implementation. To implement an interface member, the corresponding member of the implementing class must be public, non-static, and have the same name and signature as the interface member. When a class or struct implements an interface, the class or struct must provide an implementation for all of the members that the interface declares but doesn't provide a default implementation for. However, if a base class implements an interface, any class that's derived from the base class inherits that implementation.
The implementing class, Car , must provide an implementation of the Equals method. Properties and indexers of a class can define extra accessors for a property or indexer that's defined in an interface. For example, an interface might declare a property that has a get accessor.
The class that implements the interface can declare the same property with both a get and set accessor. However, if the property or indexer uses explicit implementation, the accessors must match. For more information about explicit implementation, see Explicit Interface Implementation and Interface Properties. Interfaces can inherit from one or more interfaces. The derived interface inherits the members from its base interfaces. A class that implements a derived interface must implement all members in the derived interface, including all members of the derived interface's base interfaces.
That class may be implicitly converted to the derived interface or any of its base interfaces. A class might include an interface multiple times through base classes that it inherits or through interfaces that other interfaces inherit. Java used interfaces to provide the features used by multiple inheritance.
Interfaces can also be considered an abstract class which group similar methods without any implementation. A class can implement several interfaces, thus providing similar features that are provided by multiple inheritance. The below example describes an interface and its implementation. Java is an object-oriented programming language, and the above topics form the key pillars of object-oriented programming, or we can also say that Java provides an object-oriented programming paradigm through inheritance, abstraction, and interface.
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There are four main pillars of OOPS, and they are: 1. Inheritance 2. Abstraction 3. Encapsulation 4. Inheritance In the biological world, all living organisms inherit some or all the properties of their parents. Abstraction The OOPS provides the benefit of hiding non-essential details from the end-user by providing an abstraction. Abstract Method Abstract keyword is used to declare a method abstract, and the method cannot have an implementation in the class where it is declared.
What is Multiple Inheritance? Inheritance, Abstract Class and Interface in Java Java is an object-oriented programming language, and the above topics form the key pillars of object-oriented programming, or we can also say that Java provides an object-oriented programming paradigm through inheritance, abstraction, and interface. Recent Posts. Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website.
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