Unit 3 · Classes and Objects · 7 min

The this keyword

`this` refers to the current object. It is mostly used when a parameter has the same name as a field.

Why this matters

Every real-world Java class uses this in constructors and setters, so you will see it constantly.

Real-life analogy

In a classroom, if two students are called Arjun, the teacher says 'this Arjun' while pointing. `this` is that pointing finger.

Example

Java

class Student {
    String name;
    int rollNumber;

    Student(String name, int rollNumber) {
        this.name = name;              // field = parameter
        this.rollNumber = rollNumber;
    }

    void display() {
        System.out.println(this.rollNumber + " - " + this.name);
    }
}

public class Main {
    public static void main(String[] args) {
        new Student("Ananya Rao", 12).display();
    }
}

Output

12 - Ananya Rao

Step by step

1The parameter `name` hides the field `name` inside the constructor.
2`this.name` clearly means the field of the current object.
3`name` alone means the parameter.
4Without `this`, the line `name = name;` would just assign the parameter to itself and the field would stay null.

Key points

this = reference to the current object
Solves the field/parameter name clash
this() can call another constructor of the same class
Cannot be used inside static methods

Common mistakes

Writing `name = name;` and wondering why the field is null
Using this inside main or any static method

Try it yourself

Rewrite your Book constructor using parameters with the same names as the fields plus this.
Add a setName(String name) method that uses this.

Open the practice notebook