Getting parts classes from product design

Question

I have problem with designing parts in my game library. I have more parts in separated classes (for example Matchmaking, Scheduler, Auth, EventProcessor,...).

There will be ONE instance used at runtime (There's no need for two Schedulers or Matchmaking classes). I have seen multiple ways of accessing theese classes.

In following text ProductName is the name of library and PartName is the name of class.

First way was by class called ProductName and it had static methods like ProductName.getPartName(), then the calls were ProductName.getPartName().call().
The second one was done by using singleton pattern (PartName.getInstance()), the calls were PartName.getInstance().call().
And the third one was by having all methods in class marked as static, so the calls were PartName.call()

What is the best way / best design for this?

Thanks for answers!

Best regards!

Clemencio Morales Lucas · Accepted Answer · 2014-10-13T14:24:36.427

When you need to have one and one only instance of a class in your project, you will probably need to apply the Singleton Software Pattern. With this, there will always be just one instance of the Singleton in your project. This code is an example of Singleton, with test included:

ClassicSingleton.java:

public class ClassicSingleton {
   private static ClassicSingleton instance = null;
   protected ClassicSingleton() {
      // Exists only to defeat instantiation.
   }
   public static ClassicSingleton getInstance() {
      if(instance == null) {
         instance = new ClassicSingleton();
      }
      return instance;
   }
}

SingletonTestCase.java:

import org.apache.log4j.Logger;
import junit.framework.Assert;
import junit.framework.TestCase;
public class SingletonTest extends TestCase {
   private ClassicSingleton sone = null, stwo = null;
   private static Logger logger = Logger.getRootLogger();
   public SingletonTest(String name) {
      super(name);
   }
   public void setUp() {
      logger.info("getting singleton...");
      sone = ClassicSingleton.getInstance();
      logger.info("...got singleton: " + sone);
      logger.info("getting singleton...");
      stwo = ClassicSingleton.getInstance();
      logger.info("...got singleton: " + stwo);
   }
   public void testUnique() {
      logger.info("checking singletons for equality");
      Assert.assertEquals(true, sone == stwo);
   }
}

Results:

Buildfile: build.xml
init:
     [echo] Build 20030414 (14-04-2003 03:08)
compile:
run-test-text:
     [java] .INFO main: getting singleton...
     [java] INFO main: created singleton: Singleton@e86f41
     [java] INFO main: ...got singleton: Singleton@e86f41
     [java] INFO main: getting singleton...
     [java] INFO main: ...got singleton: Singleton@e86f41
     [java] INFO main: checking singletons for equality
     [java] Time: 0.032
     [java] OK (1 test)

As you can see in the results, the two Singletons used are giving the same memory reference; Singleton@e86f41. Therefore, they are the same object, which is the desired behaviour.

Hope it helps,

Clemencio Morales Lucas.

Besides, if you want to study alternatives to the Singleton Design Pattern, you might find the following [question](http://stackoverflow.com/questions/1300655/whats-alternative-to-singleton) useful. — Clemencio Morales Lucas, Oct 13 '14 at 14:25

Getting parts classes from product design

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