Can you define methods in an interface

Only in Java 8 default methods have been introduced. Before that No. Show 9 more comments. Active Oldest Votes. Improve this answer. Aniket Kulkarni Aniket Kulkarni Also default implementations of methods. I am not using java 8. It is javac 1. Is your IDE using code compliance 8? That should not compile with 7 and below. Here's a good article. Phoenix I am also using 1.

This seems to really blur the lines between interfaces and abstract classes. Show 4 more comments. So in Java 7, static methods in interfaces cannot exist. So it explicitly states that in Java 8, they can exist. Add a comment. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. An Interface is about capabilities like a Player may be an interface and any class implementing Player must be able to or must implement move.

So it specifies a set of methods that the class has to implement. If a class implements an interface and does not provide method bodies for all functions specified in the interface, then the class must be declared abstract.

A Java library example is, Comparator Interface. If a class implements this interface, then it can be used to sort a collection. Syntax : Attention reader! Get hold of all the important Java Foundation and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready.

It is used to provide total abstraction. That means all the methods in an interface are declared with an empty body and are public and all fields are public, static and final by default. A class that implements an interface must implement all the methods declared in the interface. To implement interface use implements keyword. Why do we use interface? The reason is, abstract classes may contain non-final variables, whereas variables in interface are final, public and static.

So we make an interface and put all these common functionalities. And lets Bicycle, Bike, car …. We can now add default implementation for interface methods. This default implementation has special use and does not affect the intention behind interfaces. Suppose we need to add a new function in an existing interface.

Obviously the old code will not work as the classes have not implemented those new functions. So with the help of default implementation, we will give a default body for the newly added functions.

Then the old codes will still work. Note: these methods are not inherited. For example, a bicycle in a store could be managed by an inventory program. Instead of forcing class relationships on otherwise unrelated items, the inventory program sets up a protocol of communication. This protocol comes in the form of a set of method definitions contained within an interface.

The inventory interface would define, but not implement, methods that set and get the retail price, assign a tracking number, and so on. To work in the inventory program, the bicycle class must agree to this protocol by implementing the interface.