An interface is a reference type in Java. It is similar to class. It is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface. Along with abstract methods, an interface may also contain constants, default methods, static methods, and nested types.
An interface is similar to a class in the following ways −
An interface can contain any number of methods.
An interface is written in a file with a .java extension, with the name of the interface matching the name of the file.
The byte code of an interface appears in a .class file.
Interfaces appear in packages, and their corresponding bytecode file must be in a directory structure that matches the package name.
Declaring Interfaces
The interface keyword is used to declare an interface. Here is a simple example to declare an interface −
Example:
* File name : NameOfInterface.java */
import java.lang.*;
// Any number of import statements
public interface NameOfInterface {
// Any number of final, static fields
// Any number of abstract method declarations\
}
Interfaces have the following properties −
An interface is implicitly abstract. You do not need to use the abstract keyword while declaring an interface.
Each method in an interface is also implicitly abstract, so the abstract keyword is not needed.
Methods in an interface are implicitly public.
Example:
* File name : Animal.java */
interface Animal {
public void eat();
public void travel();
}
