What is the benefit of extending a generic by specifying the new type as actual type of generic

Question

I saw this pattern somewhere:

class A extends B {

}

This structure is a little unusual to extend a generic by specifying the new

Answer 1

You might do something like this when dealing with recursive data structures. For example, nodes in a graph or a tree could be defined as a collection of other nodes:

class Node extends AbstractList {
    ...
}

Equally you might see something like this if the abstract/generic type is meant for comparing objects of a similar type, such as is the case with java.lang.Comparable:

class MyObject implements Comparable {
    public int compareTo(MyObject other) { ... }
}