C# – Proper way to accomplish this construction using constructor chaining

ccomplex-numbersconstructorconstructor-chaining

I have an assignment for my first OOP class, and I understand all of it including the following statement:

You should create a class called ComplexNumber. This class will contain the real and imaginary parts of the complex number in private data members defined as doubles. Your class should contain a constructor that allows the data members of the imaginary number to be specified as parameters of the constructor. A default (non-parameterized) constructor should initialize the data members to 0.0.

Of course I know how to create these constructors without chaining them together, and the assignment does not require chaining them, but I want to as I just like to.

Without chaining them together, my constructors look like this:

class ComplexNumber
{
    private double realPart;
    private double complexPart;

    public ComplexNumber()
    {
         realPart = 0.0;
         complexPart = 0.0
    }

    public ComplexNumber(double r, double c)
    {
         realPart = r;
         complexPart = c;
    }
    // the rest of my class code...
}

Best Answer

Is this what you're looking for?

public ComplexNumber()
    : this(0.0, 0.0)
{
}

public ComplexNumber(double r, double c)
{
     realPart = r;
     complexPart = c;
}

Related Solutions

C++ – call a constructor from another constructor (do constructor chaining) in C++

C++11: Yes!

C++11 and onwards has this same feature (called delegating constructors).

The syntax is slightly different from C#:

class Foo {
public: 
  Foo(char x, int y) {}
  Foo(int y) : Foo('a', y) {}
};

C++03: No

Unfortunately, there's no way to do this in C++03, but there are two ways of simulating this:

You can combine two (or more) constructors via default parameters:

class Foo {
public:
  Foo(char x, int y=0);  // combines two constructors (char) and (char, int)
  // ...
};

Use an init method to share common code:

class Foo {
public:
  Foo(char x);
  Foo(char x, int y);
  // ...
private:
  void init(char x, int y);
};

Foo::Foo(char x)
{
  init(x, int(x) + 7);
  // ...
}

Foo::Foo(char x, int y)
{
  init(x, y);
  // ...
}

void Foo::init(char x, int y)
{
  // ...
}

See the C++FAQ entry for reference.

Java – Why do this() and super() have to be the first statement in a constructor

The parent class' constructor needs to be called before the subclass' constructor. This will ensure that if you call any methods on the parent class in your constructor, the parent class has already been set up correctly.

What you are trying to do, pass args to the super constructor is perfectly legal, you just need to construct those args inline as you are doing, or pass them in to your constructor and then pass them to super:

public MySubClassB extends MyClass {
        public MySubClassB(Object[] myArray) {
                super(myArray);
        }
}

If the compiler did not enforce this you could do this:

public MySubClassB extends MyClass {
        public MySubClassB(Object[] myArray) {
                someMethodOnSuper(); //ERROR super not yet constructed
                super(myArray);
        }
}

In cases where a parent class has a default constructor the call to super is inserted for you automatically by the compiler. Since every class in Java inherits from Object, objects constructor must be called somehow and it must be executed first. The automatic insertion of super() by the compiler allows this. Enforcing super to appear first, enforces that constructor bodies are executed in the correct order which would be: Object -> Parent -> Child -> ChildOfChild -> SoOnSoForth

Best Answer

Related Solutions

C++ – call a constructor from another constructor (do constructor chaining) in C++

Java – Why do this() and super() have to be the first statement in a constructor

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