A little understanding of the Android API

Java.lang.object

The object class is the ancestor of all Java classes. Each class uses Object as a superclass. All objects, including arrays, implement methods of this class.

You can see that all the classes in the official document are inherited from one layer, and those package names can be found in the SDK installation directory of Android Studio.

Lang is a shorthand for language (language)
Is the most commonly used package in Java
The description that contains the common class package Java.lang provides the basic class for programming using the Java programming language. The most important class is Object (which is the root of the class hierarchy) and class (its instance represents a class in the running application).

The Rt.jar under Jre\lib in the JDK installation directory is all of the class files.
The Src.zip in the installation directory is all the source code

A little understanding of the Android API