Interface can have method definitions too (java 1.8 ):
Explanation from Oracle :
An example that involves manufacturers of
computer-controlled cars who publish industry-standard interfaces that describe
which methods can be invoked to operate their cars. What if those
computer-controlled car manufacturers add new functionality, such as flight, to
their cars? These manufacturers would need to specify new methods to enable
other companies (such as electronic guidance instrument manufacturers) to adapt
their software to flying cars. Where would these car manufacturers declare
these new flight-related methods? If they add them to their original
interfaces, then programmers who have implemented those interfaces would have
to rewrite their implementations. If they add them as static methods, then
programmers would regard them as utility methods, not as essential, core
methods.
Default methods enable you to add new functionality to the
interfaces of your libraries and ensure binary compatibility with code written
for older versions of those interfaces.
Few important points.
- To make a method as default method it must be started with the keyword default
- You need not to override default method in the implementation class.
- Default methods are by default available in the implementation class and can be invoked using an object of implementation class.
A simple example
//interface DefaultMethod.java
interface DefaultMethod {
//abstract Method
public void methodA();
//static methods
static void methodB()
{
System.out.println("Inside Method
B");
}
//default Method
default void newDefaultMethod()
{
System.out.println("\n Default
Method");
}
}
//class
DefaultMethodImplementation.java which implements DefaultMethod interface.
public class
DefaultMethodImplementation implements DefaultMethod {
public void methodA(){
System.out.println("\n Inside
A");
}
public static void main(String[] args) {
DefaultMethodImplementation
dmi=new
DefaultMethodImplementation();
dmi.methodA();
dmi.newDefaultMethod();
}
}
