JAVA INTERFACE WITH DEFAULT METHODS HOW TO

Any method inside an Interface can’t be declared default & static together.They are not allowed inside classes, even if it is implemented class of that Interface. We can have Default methods (method with default keyword) only inside Interfaces as of Java 8.Let’s go through the table below to see the differences which are still in place. It doesn’t mean that both are similar now as we still have many differences between them. Since JDK 1.8 after the introduction of default method in interface, this difference becomes false. The major difference between the Interface & an abstract class before JDK 1.8 was that all the methods in an Interface are abstract by default while in an abstract class it is not necessary that all methods are abstract. interface Human Difference between Interface & Abstract class after introduction of default Method in Interface Further, we can’t force Implementing classes to override this method. For example, in the below code, walks() is a default method in interface Human. The default method in interface was introduced in JDK 8. We also call it defender method or virtual extension method. If we have an implemented method inside an interface with default keyword, then we will call it as a Default method. Difference between Interface & Abstract class after introduction of default Method in Interface.Resolution of Diamond Problem in context of Default methods.How can a default method save effort in writing codes?.Why do we need Default Methods/ Advantages of defining Default Method?.

JAVA INTERFACE WITH DEFAULT METHODS HOW TO

How to decide which method should be default?.So, if the implementing class does not implement the hello() method, a compilation error will occur for duplicate method declaration. Now, the implementing class extends default method behaviour from both interfaces. Let’s create two interfaces InterfaceA and InterfaceB that provide the default method hello() and a class implementing both these interfaces. Scenario 1 : Class implements both interfaces without overriding the default method here is what will happen in each of the scenarios. So, what happens when a class implements multiple interfaces with the same default method ? Java doesn’t support multiple inheritance of classes, however a class can implement multiple interfaces. Multiple inheritance issues with Default methods Since, the implementing class M圜lass didn’t override multiply(), default method behaviour was used. Now, if we create an instance of M圜lass and call the multiply() method, the default method implementation will be used as shown below : The above class M圜lass implements the MyIF interface and provides implementation of add() method. The default method can be used as is unless the implementing class wants to change the behaviour.

Note that, an implementing class is only required to implement the abstract method. Let’s create a class implementing this interface. The above interface declares an abstract method add() and a default method multiply(). Here is an example of interface with a default method : If the implementation class wants to use it, it can use it or it can ignore the default implementation and create its own implementation.Įven though an interface can now define default methods, the interface must still be implemented by a class if an instance is to be created. These methods are called default methods.Ī default method is declared using a keyword “ default” and it contains a method body.Ī default method is available to all implementing classes of the interface. Interfaces contain only constants and method signatures.īeginning JDK 8, it is possible to define default implementation for a method in an interface. Prior to JDK 8, an interface could not contain any implementation. This article explains Default Interface Methods introduced in Java8 and how to use them in multiple inheritance scenarios.

Java interface with default methods