Creating a Generic Class

Java Tutorials - Herong's Tutorial Examples - Version 7.03, by Dr. Herong Yang

Java Tutorials - Herong's Tutorial Examples

∟Generic Classes and Parameterized Types

∟Creating a Generic Class - Example

This section provides a tutorial example on creating a generic class by declaring type parameters and using them as 'Type Variable' types within the scope of the class.

Here is an example program that creates a generic class with a single type parameter:

/* ObjectRegister.java
 - Copyright (c) 2014, HerongYang.com, All Rights Reserved.
 */
import java.util.*;
class ObjectRegister<T> {
   private HashSet<T> pool;

   // Constructor
   public ObjectRegister() {
      pool = new HashSet<T>();
   }
   // Registering T objects   
   public void register(T item) {
      pool.add(item);
   }
   // Returning the size
   public long size() {
      return pool.size();
   }
   // Testing the class
   public static void main(String[] a) {
      java.io.PrintStream o = System.out;
      ObjectRegister<String> reg = new ObjectRegister<String>();
      reg.register(new String("Java"));
      reg.register(new String("C++"));
      reg.register(new String("PHP"));
      o.println("# of objects registered: "+reg.size());
   }
}

Compile and run the example, you will get: