Use Java's extends keyword to derive a child class from a parent class, invoke parent class constructors and methods, override methods, and more.

A Java class inherits these methods and can override any method that’s not declared final. For example, the non- final toString() method can be overridden, whereas the final wait() methods cannot.

Sealed classes make Java an even more powerful and expressive language and set the stage for even more sophisticated techniques such as pattern matching, which we'll explore in a subsequent article. A ...