Learn Java Tutorial 25 Interface with Example
This tutorial is made for learning about the Interface with Example of Java Programming Language.
An interface in the Java programming language is an abstract type that is used to specify an interface (in the generic sense of the term) that classes must implement. Interfaces are declared using the interface keyword, and may only contain method signature and constant declarations (variable declarations that are declared to be both static and final). All methods of an Interface do not contain implementation (method bodies) as of all versions below Java 8. Starting with Java 8, default and static methods may have implementation in the interface definition
Interfaces cannot be instantiated, but rather are implemented. A class that implements an interface must implement all of the methods described in the interface, or be an abstract class. Object references in Java may be specified to be of an interface type; in each case, they must either be null, or be bound to an object that implements the interface.
One benefit of using interfaces is that they simulate multiple inheritance. All classes in Java must have exactly one base class, the only exception being java.lang.Object (the root class of the Java type system); multiple inheritance of classes is not allowed.
A Java class may implement, and an interface may extend, any number of interfaces; however an interface may not implement an interface.
What is an interface
Interface looks like class but it is not a class. An interface can have methods and variables just like the class but the methods declared in interface are by default abstract (only method signature, no body). Also, the variables declared in an interface are public, static & final by default. We will discuss these points in detail later in this post.
What is the use of interfaces
As stated above they are used for abstraction. Since methods in interfaces does not have body, they have to be implemented by the class before you can access them. The class that implements interface must implement all the methods of that interface. Also, java programming language does not support multiple inheritance, using interfaces we can achieve this as a class can implement more than one interfaces, however it cannot extend more than one classes.
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