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:

 - Copyright (c) 2014,, 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) {
   // Returning the size
   public long size() {
      return pool.size();
   // Testing the class
   public static void main(String[] a) { 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:

# of objects registered: 3

Last update: 2014.

Table of Contents

 About This Book

 Installing JDK 1.8 on Windows

 Execution Process, Entry Point, Input and Output

 Primitive Data Types and Literals

 Bits, Bytes, Bitwise and Shift Operations

 Managing Bit Strings in Byte Arrays

 Reference Data Types and Variables

 StringBuffer - The String Buffer Class

 System Properties and Runtime Object Methods

Generic Classes and Parameterized Types

 What Is a Generic Class?

 Using a Generic Class

 Using a Generic Class - Example

 Creating a Generic Class

Creating a Generic Class - Example

 Bounded Type Parameters

 Raw Type, Generic Type and Parameterized Type

 Parameterized Type and Subtyping

 Wildcard Parameterized Types

 Wildcard Parameterized Type Test

 Wildcard Parameterized Subtyping

 Wildcard Parameterized Subtyping Example

 Generic Methods and Type Inference

 Lambda Expressions and Method References

 Execution Threads and Multi-Threading Java Programs

 ThreadGroup Class and "system" ThreadGroup Tree

 Synchronization Technique and Synchronized Code Blocks

 Deadlock Condition Example Programs

 Garbage Collection and the gc() Method

 Outdated Tutorials


 PDF Printing Version