Every Java class inherits from Object, so familiarity with this superclass is fundamental to understanding the Java class hierarchy. Also see my Java tip introducing composition vs. inheritance .

The java.base module also exports packages to other modules, such as java.lang, which contains core classes like Object and String.These packages are then loaded by the bootstrap class loader. The ...

Sealed classes, proposed in JEP 409 and available since Java 17, let developers limit and control how deeply a component's type hierarchy can extend. With sealed classes, a developer can essentially ...