How to use the properties of a class in the same class like they have values in C#-CodePudding

I am trying to use a property of a class in the same class to compare with another value. However, this property is still empty because I do not have an instance of that class. See the example below.

public Zoo(string name, int capacity)
{
    Name = name;
    Capacity = capacity;    
}
public Zoo()
{
    AnimalsWhichCouldNotBeModified = new List<Animal>();
}
public List<Animal> AnimalsWhichCouldNotBeModified { get; set; }
public string  Name { get; set; }
public int Capacity { get; set; }

public string  AddAnimal(Animal animal)
{
    // Here I have tried to use the property Capacity.
    // I have also tried to use "capacity" from the constructor.
    // I have also tried to create an instance of the Zoo class in the Zoo class, but it is still empty, so I am not sure if I can do that.  
    if (Capacity < AnimalsWhichCouldNotBeModified.Count)
    {
        return "The zoo is full.";
    }

How can I get the capacity (that is still not instanced and it is null) to be used in the example so I can check if the animals are more than the zoo capacity?

CodePudding user response：

In your second constructor (public Zoo() that doesn't require any other parameters), you could just set your Capacity = 0.

Each time an instance is created, you're either going to use the first constructor, where you need to manually provide a Capacity, or the second constructor that is automatically going to set the Capacity to value 0.

public Zoo(string name, int capacity)
{
    Name = name;
    Capacity = capacity;    
}
public Zoo()
{
    Capacity = 0;
    AnimalsWhichCouldNotBeModified = new List<Animal>();
}
public List<Animal> AnimalsWhichCouldNotBeModified { get; set; }
public string  Name { get; set; }
public int Capacity { get; set; }
public string  AddAnimal(Animal animal)
{
    // Here I have tried to use the property Capacity.
    // I have also tried to use "capacity" from the constructor.
    // I have also tried to create an instance of the Zoo class in the Zoo class, but it is still empty, so I am not sure if I can do that.  
    if (Capacity < AnimalsWhichCouldNotBeModified.Count)
    {
        return "The zoo is full.";
    }
}

CodePudding user response：

The problem is you don't initialize AnimalsWhichCouldNotBeModified in the non-default constructor. You can either add the initialization into the non-default constructor:

public Zoo(string name, int capacity)
{
    Name = name;
    Capacity = capacity;    
    AnimalsWhichCouldNotBeModified = new List<Animal>();
}

or call the default one from the non-default:

public Zoo(string name, int capacity) : this()
{
    Name = name;
    Capacity = capacity;    
}

public Zoo()
{
    AnimalsWhichCouldNotBeModified = new List<Animal>();
}

or, third option, provide an initializer in the property's declaration:

public List<Animal> AnimalsWhichCouldNotBeModified { get; set; } = new List<Animal>();

I'd personally prefer this third option unless I needed a more complex initialization code in the constructor.

Note that when Capacity is not initialized, it will be 0 by default. This is because the underlying (compiler-generated) backing field is initialized to 0. The same holds for AnimalsWhichCouldNotBeModified and Name which are null by default.