Generic Class Hierarchies: uses a generic superclass : Generic Class Hierarchies « Generics « Java Tutorial

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2. Generics
3. Generic Class Hierarchies

In a generic hierarchy, any type arguments needed by a generic superclass must be passed up the hierarchy by all subclasses.

class Gen<T> { 
  T ob;
   
  Gen(T o) { 
    ob = o; 
  } 
 
  T getob() { 
    return ob; 
  } 
} 

class Gen2<T> extends Gen<T> {
  Gen2(T o) {
    super(o);
  }
}