Can an interface method have a body?

I know that an interface is like a 100% pure abstract class. So, it can't have method implementation in it. But, I saw a strange code. Can anyone explain it?

Code Snippet:

 interface Whoa {
        public static void doStuff() {
            System.out.println("This is not default implementation");
        }
 }

EDIT:

My IDE is Intellij Idea 13.1. The project SDK is java 7 <1.7.0_25>. The IDE is not showing any compiler error. But, When I compile the code at command line I am getting the following message.

> Whoa.java:2: error: modifier static not allowed here > public static void doStuff() { > ^

From Java 8 you can define static methods in interfaces in addition to default methods.

• A static method is a method that is associated with the class in which it is defined rather than with any object. Every instance of the class shares its static methods.

• This makes it easier for you to organize helper methods in your libraries; you can keep static methods specific to an interface in the same interface rather than in a separate class.

• The following example defines a static method that retrieves a ZoneId object corresponding to a time zone identifier; it uses the system default time zone if there is no ZoneId object corresponding to the given identifier. (As a result, you can simplify the method getZonedDateTime)

Here is code :

public interface TimeClient {
   // ...
    static public ZoneId getZoneId (String zoneString) {
        try {
            return ZoneId.of(zoneString);
        } catch (DateTimeException e) {
            System.err.println("Invalid time zone: " + zoneString +"; using default time zone instead.");
            return ZoneId.systemDefault();
        }
    }

   default public ZonedDateTime getZonedDateTime(String zoneString) {
      return ZonedDateTime.of(getLocalDateTime(), getZoneId(zoneString));
   }    
}

See also

• Oracle docs for interface methods

• For all interesting things in Java 8 read Everything about Java 8

This is only possible in Java 8. In the Java 7 Language Specification §9.4, it explicitly states:

> It is a compile-time error if a method declared in an interface is declared static, because static methods cannot be abstract.

So in Java 7, static methods in interfaces cannot exist.

If you go to the Java 8 Language Specification §9.4.3, you can see that it says:

> A static method also has a block body, which provides the implementation of the method.

So it explicitly states that in Java 8, they can exist.

I even tried to run your exact code in Java 1.7.0_45, but it gave me the error "modifier static not allowed here".

---

Here is a quote directly from the Java 8 tutorial, Default Methods (Learning the Java Language > Interfaces and Inheritance):

> ## Static Methods > > In addition to default methods, you can define static methods in > interfaces. (A static method is a method that is associated with the > class in which it is defined rather than with any object. Every > instance of the class shares its static methods.) This makes it easier > for you to organize helper methods in your libraries; you can keep > static methods specific to an interface in the same interface rather > than in a separate class. The following example defines a static > method that retrieves a ZoneId object corresponding to a time > zone identifier; it uses the system default time zone if there is no > ZoneId object corresponding to the given identifier. (As a result, > you can simplify the method getZonedDateTime): > > public interface TimeClient { > // ... > static public ZoneId getZoneId (String zoneString) { > try { > return ZoneId.of(zoneString); > } catch (DateTimeException e) { > System.err.println("Invalid time zone: " + zoneString + > "; using default time zone instead."); > return ZoneId.systemDefault(); > } > } >
> default public ZonedDateTime getZonedDateTime(String zoneString) { > return ZonedDateTime.of(getLocalDateTime(), getZoneId(zoneString)); > }
> } > > Like static methods in classes, you specify that a method definition > in an interface is a static method with the static keyword at the > beginning of the method signature. All method declarations in an > interface, including static methods, are implicitly public, so you > can omit the public modifier.

For java version 7 or below, similar functionally you can achieve using nested class declared within interface body. and this nested class implements outer interface.

Example:

interface I1{
    public void doSmth();

    class DefaultRealizationClass implements  I1{

        @Override
        public void doSmth() {
           System.out.println("default realization");
        }
    }
}

How do we use it in our code?

class MyClass implements I1{

    @Override
    public void doSmth() {
         new I1.DefaultRealizationClass().doSmth();
    }   
}

Therefore default implementation encapsulated within interface.