The interface in Java is a mechanism to achieve abstraction. There can be only abstract methods in the Java interface, not method body. It is used to achieve abstraction and multiple inheritance in Java.
An interface can have methods and variables, but the
methods declared in an interface are by default abstract.
- Like abstract classes, interfaces cannot be
used to create objects
- Interface methods do not have a body - the body is provided by the
"implement" class
- On implementation of an interface, you must override all of its
methods
- Interface methods are by default abstract and public
- Interface attributes are by
default public, static and final
- An interface cannot contain a constructor (as it cannot be used to
create objects)
An interface is declared by using the interface
keyword. A class that implements an interface must implement all the methods
declared in the interface.
interface <interface_name>{
//
declare constant fields
// declare
methods that abstract
// by
default.
}
To implement an interface we use keyword: implements
Example:
// Java program to demonstrate working of
// interface.
import java.io.*;
// A simple interface
interface Inf
{
//
public, static and final
final
int a = 10;
//
public and abstract
void
display();
}
// A class that implements the interface.
class TestClass implements Inf
{
public
void display()
{
System.out.println("Java");
}
public static void main (String[] args)
{
TestClass
t = new TestClass();
t.display();
System.out.println(a);
}
}
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