![]() ![]() ![]() These features allow us to add new functionality in the interfaces without breaking the existing. Adding default methods to an interface doesn’t break the existing code, hence interfaces in Java now can evolve over time. Java 8 introduced default and static methods in interfaces. So, if a developer wanted to add a new method to an interface, then the implementation code must. Developers had to provide the implementation of these methods in a separate class. Before default methods in Java 8, interfaces could only have abstract methods. But that’s not the only use of static method in interface.So far you have learned about default methods in interface in Java. The default methods were primarily introduced to resolve compatibility issues in Java. For example, the new methods added to the Collection interface are declared as follows: public interface Collection Since static methods do not belong to instances of class and are not inherited, they are perfect to be reused by default methods, as seen in the above example. default methods are overridable methods, but your scenario describes a utility method that is intended to be neither, part of the API nor overridable. A default method is declared with the default modifier before the return type, and it contains method body (implementation). ![]() For example, ‘List’ or ‘Collection’ interfaces do not have ‘forEach’ method declaration. This capability is added for backward compatibility so that old interfaces can be used to leverage the lambda expression capability of Java 8. And worse, there are also countless of classes written by programmers that depend on the Collection inheritance tree – causing their applications to fail if the new methods added to Collection interface works the old way: concrete classes must implement methods declared in its super interfaces.Therefore, the designers of Java language decided to introduce default methods for interface. Default methods enable you to add new functionality to existing interfaces and ensure binary compatibility with code written for older versions of those interfaces. Java 8 introduces a new concept of default method implementation in interfaces. For example, the Collection interface needs to add two methods sort() and stream() - as illustrated in the following class diagram: However, there are many sub interfaces and implementation classes in the Collection inheritance tree – so adding new methods to the Collection interface will break these existing classes – require them to implement the new methods. This article helps you understand why default methods are needed and how to use them.You know, Java 8 comes with some new features like Streams and Lambda expressions which require adding of some new methods in the core interfaces of the Java Collections framework. Since Java 8, an interface can have default methods with concrete implementation. ![]()
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