C#
The this keyword
Learn to reference the class itself with this.
What is this?
The this keyword refers to the current instance. Its most common use is to distinguish a field from a parameter that shares the same name: this.name = name;.
Here this.name refers to the class field, while name refers to the method parameter. Without this, name = name assigns the parameter to itself; the field stays unchanged. That is why this is essential in shadowing situations.
Why this qualification matters
When a parameter shares the field's name, the compiler prefers the parameter. In name = name; both sides refer to the parameter; the field never changes. This is a silent bug and the code still compiles.
The this prefix tells the compiler that the left side is the class field, so the assignment works correctly. Rule: when parameter and field share a name, always use this. You can also avoid this entirely by choosing different names.
Exercise Use this in the Student class
The Student class already has private string name;. Add a public void SetName(string name) method with this.name = name; in the body. Also add a public string GetName() method with return name;. Inside Main call SetName("Alex") and print with GetName().
Show example solution
In SetName write this.name = name;. In GetName write return name;. In Main add s.SetName("Alex"); Console.WriteLine(s.GetName());.
Example solution:
using System;
class Student
{
private string name;
public void SetName(string name)
{
this.name = name;
}
public string GetName()
{
return name;
}
}
class Program
{
static void Main()
{
Student s = new Student();
s.SetName("Alex");
Console.WriteLine(s.GetName());
}
}
Test yourself
-
What does this.name = name; do?
public void SetName(string name) { this.name = name; }
- Assigns the parameter name to the class field name
- Declares a new local variable
- Ignores the parameter
- Resets the class
Show answer
Assigns the parameter name to the class field name — Correct. this.name is the field, name is the parameter.
-
Complete the assignment with this
public void SetName(string name) { this.name = ____; }
Show answer
public void SetName(string name) { this.name = name; }
-
Match each this usage to its purpose
- this.name = name
- Separate field from parameter
- this
- Current instance
- this.Greet()
- Call own method
- name = name
- Self assignment (no-op)
Next lesson: Object initialization
