OOPS (Design Patterns)

Question

hey, hi i want put limit on object creation means a class can have at most suppose 4 objects not more than that how to achieve this?

It is language dependent. Which language are you interested in? — , Feb 24 '10 at 05:14
It's worth reading Steve Yegge's condemnation of the Singleton pattern, and see if any of those warnings apply to you: http://steve.yegge.googlepages.com/singleton-considered-stupid Clients of your class shouldn't know that there are limited instances of the class. For one thing, that makes it harder to unit test. — RossFabricant, Feb 24 '10 at 05:50
What should the behaviour be on the request for the 5th object instance? — Philip Fourie, Feb 25 '10 at 07:59

score 10 · Accepted Answer · answered Feb 24 '10 at 05:12

10

One approach is using an object factory that creates at most 4 instances. It's an interesting need... Would an object pool serve the same need?

answered Feb 24 '10 at 05:12

marklai

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+1 for both limited Factory and Object Pool. – LiraNuna Feb 24 '10 at 05:14
A Factory class with an object pool or cache would be the way to go here – Lars Mæhlum Mar 11 '10 at 08:52

score 3 · Answer 2 · answered Feb 24 '10 at 05:13

You can count the numbers of instances created by using a static class property to store the count. This can either be done in the class constructor or you can make use of a factory pattern. It is a bit difficult to answer this more precisely without knowing the target language.

score 3 · Answer 3 · answered Feb 24 '10 at 05:15

3

Try modifying the Singleton pattern. You can use a count variable. You'll need to keep the Constructor private to have control over the no. of instances.

answered Feb 24 '10 at 05:15

Padmarag

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That variant is called the MultiTon :) – malaverdiere Feb 24 '10 at 05:59

score 1 · Answer 4 · answered Mar 11 '10 at 08:47

One way to achieve is the Singleton Design pattern, Whenever we make a call to create an instance, check the count of the instance which are already created, if the instance count is already reached 4, then use the same instance for your application. TO have a count, Creat Static Int Counter = 0; and keep incrementing it to get the results.

Mike Trpcic · Answer 5 · 2010-02-28T21:38:18.507

0

The simplest way to do this would be to have a class level attribute called "count", and in your constructor, just make sure that "count" isn't above a certain number.

//pseudocode
class foo
  static count = 0

  def constructor()
    if count < 4
      //create object
    else
      //there are too many!

edited Feb 28 '10 at 21:38

answered Feb 24 '10 at 05:15

Mike Trpcic

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In this case, each object will have its own copy of count, which'll always be 0. The count variable needs to be static. – Padmarag Feb 24 '10 at 05:17
It's pseudo code, it doesn't need to be perfect. – Mike Trpcic Feb 24 '10 at 14:48
but at leat the essential should be right (as they are now) – peterchen Apr 19 '10 at 11:10

score 0 · Answer 6 · edited Apr 19 '10 at 11:20

This is short code snippest that will give the above result in c#

sealed class clsInstance
    {
        public static int count = 0;
        private static readonly clsInstance inst = new clsInstance();
        clsInstance()
        {

        }

        public static clsInstance Inst
        {
            get
            {
                if (count < 4)
                {

                    Console.WriteLine("object : " + count);
                    count++;
                    return inst;
                }
                return null;
            }
        }


    }

   class MainClass
   {
       public static void Main(String[] args)
       {
           clsInstance c1 = clsInstance.Inst;
           clsInstance c2 = clsInstance.Inst;
           clsInstance c3 = clsInstance.Inst;
           clsInstance c4 = clsInstance.Inst;
           Console.ReadLine();
           clsInstance c5 = clsInstance.Inst;
           Console.ReadLine();
       }
   }

OOPS (Design Patterns)

6 Answers6

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