Java8 07 Why Default Method have been introduced in java8
Topics:
-feature Default Methods In Java 8
-Why default method have been added .
-Default Methods and Multiple Inheritance
Next Topic Interface vs Abstract Class in Java8
Interfaces can have default methods with implementation in Java 8 on later.
Interfaces can have static methods as well, similar to static methods in classes.
Default methods were introduced to provide backward compatibility for old interfaces so that they can have new methods without affecting existing code
Static default methods: You can define static default methods in interface which will be available to all instances of class which implement this interface.
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. This enables you to define methods out of your class and yet share with all child classes.
Why default methods were needed in java 8?
Simplest answer is to enable the functionality of lambda expression in java.
Lambda expression are essentially of type of functional interface. To support lambda expressions seamlessly,
all core classes have to be modified. But these core classes like java.util.List are implemented not only in JDK classes,
but also in thousands of client code as well. Any incompatible change in core classes will back fire for sure and will not be accepted at all.
Rules for this conflict resolution are as follows:
1) Most preferred are the overridden methods in classes. They will be matched and called if found before matching anything.
2) The method with the same signature in the “most specific default-providing interface” is selected.
This means if class Animal implements two interfaces i.e. Moveable and Walkable such that Walkable extends Moveable.
Then Walkable is here most specific interface and default method will be chosen from here if method signature is matched.
3) If Moveable and Walkable are independent interfaces then a serious conflict condition happen,
and compiler will complain then it is unable to decide. The you have to help compiler by providing extra info that from which interface
the default method should be called. e.g.
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