7.3. Instance constructors

Instance constructors in C# are simply Java constructors. The reason for the name is because there is another group of constructors in C# called static constructors (see section 7.4).

Here is an example of a class with overloaded instance constructors.

 1: using System;
 2:
 3: public class Test{
 4:   public static void Main(){
 5:     Test t1 = new Test();
 6:     Test t2 = new Test("Here is a string");
 7:   }
 8:
 9:   // overloaded instance constructors
10:   public Test(){
11:     Console.WriteLine("Running default constructor");
12:   }
13:   public Test(string i){
14:     Console.WriteLine("Running constructor with param");
15:   }
16: }

Output:

c:expt>test
Running default constructor
Running constructor with param

Like Java

• Instance constructors must have the same name (and case) as the immediately enclosing class, and cannot return a value.

• Constructors are special methods of a class that will always be called when an instance of that class is first created.

• The rule of constructor chaining still applies – invoking the constructor of a class always invokes the constructor of its superclass recursively all the way to System.Object.

• Unlike other methods, constructors are not inherited to subclasses.

• You can overload constructors.

• A default constructor ^[5] is provided if no constructor is explicitly coded in the class. However, when at least one constructor is coded in a class, the default constructor will not be provided implicitly.

  ^[5] A default constructor refers to the constructor which takes in no parameters.

• You can use the this keyword to invoke an overloaded constructor in the same class (see section 7.6).