Java interface default method8/16/2023 ![]() But that’s not the only use of static method in interface.So far you have learned about default methods in interface 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. A default method is declared with the default modifier before the return type, and it contains method body (implementation). 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. 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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