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.

Last but not least, you get to learn all about inner classes and their classifications within Java. Inner classes are used to logically group classes and interfaces in one place so that your code ...

The functional Predicate interface gets used extensively by the Java 8 Streams API. Any developer who wants to master functional programming in Java will need to be comfortable with the Predicate ...

Developers can use familiar Java classes and interfaces to interact with the database, making it straightforward to perform database operations such as creating tables, inserting data, querying ...

Another type of class that wasn't in Java 11 but that you will find in Java 17 is sealed classes. Sealed classes and interfaces are designed to allow you to control which of the other classes are ...

For an introduction to Java interfaces, including the difference between classes and interfaces, see my Java 101 tutorial Working with interfaces in Java. Nesting interfaces in classes.