How constructor chaining works in C Sharp (C#) - Visual Walkthrough

Concept Flow - How constructor chaining works

Call constructor A

↓

Constructor A calls Constructor B

↓

Constructor B executes

↓

Return to Constructor A

↓

Constructor A completes

↓

Object fully constructed

Constructor chaining means one constructor calls another to reuse code, running the called constructor first before finishing the caller.

Execution Sample

C Sharp (C#)

class Person {
  public string Name;
  public int Age;

  public Person() : this("Unknown", 0) {}
  public Person(string name, int age) {
    Name = name; Age = age;
  }
}

This code shows a default constructor calling another constructor with parameters to set default values.

Execution Table

Step	Constructor Called	Parameters	Action	State Change
1	Person()	none	Calls Person(string, int) with ("Unknown", 0)	No state change yet
2	Person(string, int)	("Unknown", 0)	Sets Name = "Unknown", Age = 0	Name="Unknown", Age=0
3	Person()	none	Returns after Person(string, int) completes	Name="Unknown", Age=0
4	Person()	none	Constructor completes, object created	Final state: Name="Unknown", Age=0

💡 Constructor chaining ends after the called constructor finishes and control returns to the caller.

Variable Tracker

Variable	Start	After Step 2	After Step 4
Name	null	"Unknown"	"Unknown"
Age	0	0	0

Key Moments - 2 Insights

Why does the parameterized constructor run before the default constructor finishes?

Because constructor chaining calls the other constructor first (see execution_table step 1 and 2), so the called constructor sets values before the caller continues.

What happens if the chained constructor is missing?

The code will not compile because the chaining call (': this(...)') requires the target constructor to exist, as shown in the code sample.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of Name after step 2?

A "Unknown"

B null

C "" (empty string)

D 0

💡 Hint

Check the 'State Change' column at step 2 in execution_table.

At which step does the Person(string, int) constructor complete?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Constructor Called' and 'Action' columns in execution_table.

If the default constructor did not chain to the parameterized one, what would happen?

A The program would crash at runtime.

B The parameterized constructor would run anyway.

C Name and Age would remain uninitialized (null and 0).

D The object would have random values.

💡 Hint

Refer to the code sample and understand that without chaining, default constructor sets nothing.

Concept Snapshot

Constructor chaining in C# lets one constructor call another using ': this(...)'.
The called constructor runs first, setting up values.
This avoids repeating code in multiple constructors.
If chaining is missing, each constructor runs independently.
Use chaining to keep initialization consistent and simple.

Full Transcript

Constructor chaining means one constructor calls another constructor in the same class to reuse code. When you create an object, the called constructor runs first, setting up initial values, then control returns to the original constructor to finish. For example, a default constructor can call a parameterized constructor with default values. This way, you avoid repeating code. If the chained constructor does not exist, the code will not compile. Without chaining, constructors run independently and may leave variables uninitialized. This process ensures consistent object setup and cleaner code.