BE THE CODER > Design Patterns > Java Design Patterns

This example shows creating an Nton. Means the application is provided with N-instances of a particular class. Each call to getInstance method is served with one of the available instances in round robin fashion. The number of instances required by the application is configurable.

Behaviour & Advantages

File Name :	com/bethecoder/tutorials/dp/singleton/nton/Nton.java
Author :	Sudhakar KV
Email :	[email protected]


package com.bethecoder.tutorials.dp.singleton.nton;



import java.util.ArrayList;

import java.util.List;



public class Nton {



  /**

   * Configure the number of instances required in the application.

   */

  private static final int NUM_OF_INSTANCES = 5;

  private static final List<Nton> instanceList = new ArrayList<Nton>();

  private static int instanceRequestCount = 0;

  private int instanceNum;

  

  /**

   * Make sure to have private default constructor.

   * This avoids direct instantiation of class using 

   * new keyword/Class.newInstance() method

   */

  private Nton() {

  }

  

  public static synchronized Nton getInstance() {

    

    Nton instance = null;

    

    if (instanceList.size() == NUM_OF_INSTANCES) {

      instance = instanceList.get(instanceRequestCount % NUM_OF_INSTANCES);

    } else {

      instance = new Nton();

      instance.instanceNum = instanceList.size() + 1;

      instanceList.add(instance);

    }

    

    instanceRequestCount ++;

    return instance;

  }

  

  public int getInstanceNum() {

    return instanceNum;

  }

  

  public String toString() {

    return "Nton : " + getInstanceNum();

  }

  

}

File Name :	com/bethecoder/tutorials/dp/singleton/nton/Test.java
Author :	Sudhakar KV
Email :	[email protected]


package com.bethecoder.tutorials.dp.singleton.nton;



public class Test {

  

  public static void main (String [] args) {

    

    for (int i = 0 ; i < 20 ; i ++) {

      System.out.println(Nton.getInstance());

    }

    

  }

}