Generic Class Hierarchies in Java

17 May, 2021
Generic means parameterized types introduced in java5. These help in creating classes, interfaces, methods, etc. A class or method which works on parameterized type known as “generic class ” or “generic method”. Generics is a combination of language properties of the definition and use of Generic types and methods. Collections were used before Generics which holds any type of objects i.e. non-generic. Using Generics, it has become possible to create a single class, interface, or method that automatically works with all types of data(Integer, String, Float, etc). It has expanded the ability to reuse the code safely and easily. Generics also provide type safety (ensuring that an operation is being performed on the right type of data before executing that operation). 
Hierarchical classifications are allowed by Inheritance. Superclass is a class that is inherited. The subclass is a class that does inherit. It inherits all members defined by super-class and adds its own, unique elements. These uses extends as a keyword to do so.
Sometimes generic class acts like super-class or subclass. In Generic Hierarchy,  All sub-classes move up any of the parameter types that are essential by super-class of generic in the hierarchy. This is the same as constructor parameters being moved up in a hierarchy.
Example 1: Generic super-class
Java
// Java Program to illustrate generic class hierarchies // Importing all input output classesimport java.io.*; // Helper class 1// Class 1 - Parent classclass Generic1<T> {    // Member variable of parent class    T obj;     // Constructor of parent class    Generic1(T o1) { obj = o1; }     // Member function of parent class    // that returns an object    T getobj1() { return obj; }} // Helper class 2// Class 2 - Child classclass Generic2<T, V> extends Generic1<T> {    // Member variable of child class    V obj2;    Generic2(T o1, V o2)    {        // Calling super class using super keyword        super(o1);         obj2 = o2;    }     // Member function of child class    // that returns an object    V getobj2() { return obj2; }} // Class 3 -  Main classclass GFG {       // Main driver method    public static void main(String[] args)    {        // Creating Generic2 (sub class) object      // Custom inputs as parameters        Generic2<String, Integer> x            = new Generic2<String, Integer>("value : ",                                            100);         // Calling method and printing        System.out.println(x.getobj1());        System.out.println(x.getobj2());    }}
value : 
100
Note: A subclass can freely add its own type parameters, if necessary. 
Example 2: Non-generic sub-class of generic sub-class
Java
import java.io.*;// non-generic super-classclass NonGen {    int n;    NonGen(int i) { n = i; }    int getval() { return n; }}// generic class sub-classclass Gen<T> extends NonGen {    T obj;    Gen(T o1, int i)    {        super(i);        obj = o1;    }    T getobj() { return obj; }} class GFG {    public static void main(String[] args)    {         Gen<String> w = new Gen<String>("Hello", 2021);         System.out.println(w.getobj() + " " + w.getval());    }}
Hello 2021
 
gabaa406
Java-Generics
Technical Scripter 2020
Java
Technical Scripter
Java
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.