Using Constructors and Destructors in C# (C Sharp)

Constructors in C#:

Constructors are mainly used and triggered while instantiating a class. Here is a simple example to demonstrate constructors:
class sampleClass {
int member1, member2;
public sampleClass() {
member1= 10;
member2 = 20;
}
public sampleClass(int member1, int member2) {
this.member1 = member1;
this.member2 = member2;
}
public void displayData() {
Console.WriteLine(“member1 = {0}, member2 = {1}”);
}
}
public class testClass {
public static void Main() {
sampleClass obj1 = new sampleClass();
obj1.displayData();
sampleClass obj2 = new sampleClass(100, 200);
obj2.displayData();
}
}

Output of this code will be:
member1 = 10, member2 = 20
member1 = 100, member2 = 200

In this example, you have overloaded constructors in sampleClass and triggered constructors while instantiating the class. This is just a simple example. There are much more interesting characteristics about constructors. They are mentioned below:

• Even if no constructors are defined, default constructor will be executed internally
• From one constructor, you can call another constructor
• Constructors cannot be inherited
• From derived class constructor, you can call base class constructor
• Constructors can be overloaded as shown in the example above
• Constructors of a class can be classified into private constructors, instance constructors and static constructors. The example shown above is an example of instance constructor
• Constructors should not have a return type since they are already returning instance of the class

Destructors in C#:

You already know that garbage collector does the cleanup for you. But they deal with only managed resources. If your object is accessing any unmanaged resource, then you can release then inside the destructor. A destructor can be defined in a class as shown below:

class sampleClass {
~sampleClass(){
Console.WriteLine(“In Destructor method of sampleClass”);
}
}

Certain guidelines have to be followed when you use destructors in your code:

• Unlike constructors, your class can have only one destructor
• You cannot overload destructors
• You cannot inherit destructors
• You cannot make an explicit call to destructors. Destructors will be triggered in an automatic way
• You cannot associate any access modifiers to destructors
• You cannot associate any parameters to the destructors

Constructors and Destructors – Order of Execution during Inheritance:

An interesting feature about constructors and destructors is their order of execution when they are involved in inheritance. Consider the following example which deals with constructors and destructors in multilevel inheritance:

class baseClass {
public baseClass() {
Console.WriteLine(“Executing Constructor of baseClass”);
}
~ baseClass() {
Console.WriteLine(“Executing Destructor of baseClass”);
}
}
class level1:baseClass {
public level1() {
Console.WriteLine(“Executing Constructor of level1”);
}
~ level1() {
Console.WriteLine(“Executing Destructor of level1”);
}
}
class level2:level1 {
public level2() {
Console.WriteLine(“Executing Constructor of level2”);
}
~ level1() {
Console.WriteLine(“Executing Destructor of level2”);
}
}
class testClass {
public static void Main() {
level2 obj = new level2();
Console.WriteLine(“Object Instantiation successful!”);
obj = null;
Console.WriteLine(“Releasing Object and Forcing Garbage Collection…”);
GC.Collect();
}
}

Output of this code will be:

Executing Constructor of baseClass
Executing Constructor of level1
Executing Constructor of level2
Object Instantiation successful!
Releasing Object and Forcing Garbage Collection…
Executing Destructor of level2
Executing Destructor of level1
Executing Destructor of baseClass

Note that destructor is executed in the reverse order when compared to the constructor execution. Even if you release object, it is up to the garbage collector to decide when to clean it. Only when garbage collector does the cleanup, the destructors will be executed.

Hence to demonstrate the order of execution, garbage collection is forced to happen as soon as the object is released. This is done by calling GC.Collect() method. But you should avoid calling this method in your code as it has a performance overhead.

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