In this Java 101 tutorial, I’ve explained how interfaces differ from classes, and showed you how to declare, implement, and extend interfaces in your Java programs.

See the Java 101 Java interfaces tutorial for a more in-depth introduction to using interfaces in your Java programs, including where and where not to use default, static, and private methods.

When you run the inner class example, the output would be nine. Java’s Function and lambda expression example. Of course, the whole idea of the functional interface is to incorporate lambda ...

Java Supplier interface tutorial. As you can see, the code for the class that implements Java’s Supplier interface is fairly simple. The only requirements are the class declaration and the ...

The release of Java SE 15 in Sept 2020 will introduce "sealed classes" (JEP 360) as a preview feature. A sealed class is a class or interface which restricts which other classes or interfaces may ...