In other words, what you have here is an Inheritance tree, NOT Multiple
Inheritance.

Object
|
|
\|/
HttpServlet
|
|
\|/
Custom Class

In Java, each class  may directly inherit from only 1 other class, but
may inherit indirectly from as many classes as necessary. All classes
inherit from Object, either directly or indirectly. Your Custom Class
inherits from HttpServlet directly and Object indirectly.