How do I restrict object creation not more than 3 in Java class?

Question

How do I restrict object creation not more than 3 in Java class?

Can you give me an idea of how I can to do it?

Answer 1

public class LimitClass {
    private static List<LimitClass> ObjectPool = new ArrayList<LimitClass>();
    public static int objCount = 0;
    private static Random randomizer = new Random();
    private LimitClass(){
        objCount++;
    }
    public static synchronized LimitClass getLimInstance(){
        if(objCount < 3 ){
            LimitClass lc = new LimitClass();
            ObjectPool.add(lc);
            return lc;
        }
        return ObjectPool.get(randomizer.nextInt()%3);
    }
}

public class LimitObjectCreationTest {
    public static void main(String[] args) {
        LimitClass obj1 = LimitClass.getLimInstance();
        LimitClass obj2 = LimitClass.getLimInstance();
        LimitClass obj3 = LimitClass.getLimInstance();
        LimitClass obj4 = LimitClass.getLimInstance();
        LimitClass obj5 = LimitClass.getLimInstance();
        LimitClass obj6 = LimitClass.getLimInstance();
        System.out.println(obj1);
        System.out.println(obj2);
        System.out.println(obj3);
        System.out.println(obj4);
        System.out.println(obj5);
        System.out.println(obj6);
        System.out.println(obj3);  
    }
}




    LimitClass@1788a393
    LimitClass@460c2da6
    LimitClass@4283a56d
    LimitClass@460c2da6
    LimitClass@1788a393
    LimitClass@4283a56d
    LimitClass@4283a56d

Answer 2

You need Modified Singleton. See this - same OOPS (Design Patterns)

Answer 3

You need to modify singleton and create three objects.ans write three method in every method return object like as return different three objects and use when you needed. it main use no need to declare variable or object as static, because always return same object.

Answer 4

We can restrict the creation of Object for a particular class by little modification in Singleton design pattern as below:

public class LimitClass {

    private static LimitClass limInstance;
    public static int objCount = 0;

    private LimitClass(){
        objCount++;
    }

    public static synchronized LimitClass getLimInstance(){
        if(objCount < 3 ){
            limInstance = new LimitClass();
        }
        return limInstance;
    }
}

public class LimitObjectCreationTest {

    public static void main(String[] args) {

        LimitClass obj1 = LimitClass.getLimInstance();
        LimitClass obj2 = LimitClass.getLimInstance();
        LimitClass obj3 = LimitClass.getLimInstance();
        LimitClass obj4 = LimitClass.getLimInstance();
        LimitClass obj5 = LimitClass.getLimInstance();
        LimitClass obj6 = LimitClass.getLimInstance();

        System.out.println(obj1);
        System.out.println(obj2);

        System.out.println(obj3);
        System.out.println(obj4);
        System.out.println(obj5);
        System.out.println(obj6);
      }
}

Output of above code is like:

com.pack2.LimitClass@19821f
com.pack2.LimitClass@addbf1
com.pack2.LimitClass@42e816
com.pack2.LimitClass@42e816
com.pack2.LimitClass@42e816
com.pack2.LimitClass@42e816

After creation of three different object it is repeating the same 3rd object again and again. It is not creating the different object.

Answer 5

You can also have a look at ObjectPool of Apache Commons. The source code is freely available...

Answer 6

Factory pattern is the way to go. Or a static counter can be used. Need to careful about thread safety.