C# Trivia Question

Karthi Ramar

Can anyone provide the steps or source code using C#.net for the below problem??

Define a class "A" having a private field "int a" and guarantee that at any moment of time there are no more than 10 instances of that class in a program, having different "a" value.

6 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes14y ago
Accepted answer
As this question may be of general interest and it'll take me much longer to explain how to do it than to do it, I've coded it for you below.

However, Sam's right that you should first make an attempt at these questions and only ask on here for help if you get stuck:

using System;
using System.Collections.Generic;
using System.Threading;

class A
{
int a;

public int GetField()
{
return a;
}

static List list = new List(10);

public static int Count
{
get { return list.Count; }
}

public static A Create(int a)
{
if (Count < 10)
{
// check that the proposed new instance doesn't have the same 'a' as an existing instance

if (!list.Contains(a))
{
A instance = new A(a);
list.Add(a);
return instance;
}
else
{
Console.WriteLine("An instance of A with a field value of {0} already exists", a);
return null;
}
}
else
{
Console.WriteLine("There are already 10 instances of A in existence");
return null;
}
}

private A(int a)
{
this.a = a;
}

~A()
{
list.Remove(a);
}
}

class Test
{
static void Main()
{
A[] aa = new A[11];

for(int i = 0; i < 11; i++)
{
aa[i] = A.Create(i);
}

Console.WriteLine(A.Count); // 10
aa[0] = null;
aa[1] = null;
GC.Collect();
Thread.Sleep(200);
Console.WriteLine(A.Count); // 8
aa[0] = A.Create(2);
aa[1] = A.Create(0);
Console.WriteLine(A.Count); // 9
Console.ReadKey();
}
}
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Karthi Ramar14y ago
Thanks a lot sir.... this concepts helps me a lot...i just modified according to my boss requirements
0
Vulpes14y ago
The program works by keeping track of the number of instances of A that have been created.

It does this by storing the value of the field, 'a', in a list. The number of values in this list represents the number of instances currently in existence.

The user can only create a new instance by calling A's static Create method.

This method first checks that there are less than 10 instances in existence and, if there are, it then checks that the value of 'a' for the proposed new instance is not the same as the value of 'a' for an existing instance.

If everything's OK, it create the new instance (by calling A's private constructor), adds the value of 'a' to the list and returns a reference to the new instance to the caller.

If everything's not OK, it prints an appropriate message to the console and returns 'null' to the caller.

When an instance is no longer referenced and is about to be destroyed by the garbage collector, A's destructor is called by the system and removes the instance's 'a' value from the list.
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Karthi Ramar14y ago
Thank u so much...Please give some more explanation sir..
0
Karthi Ramar14y ago
Thanks for ur comment. I just want the steps for the problem. I didnt ask full source code sir
0
Sam Hobbs14y ago
This is a class assignment question. You should try to figure it out, then ask about something specific about the problem.
0