The this Keyword

What this Means

Inside an instance method or constructor, this is a reference to the current object, the object on which the method was called.

Use	Example	Why
Separate field from parameter	`this.name = name;`	parameter hides the field with the same name
Call another constructor	`this("Guest");`	reuse constructor code
Pass the current object	`cart.add(this);`	give other code a reference to yourself
Return the current object	`return this;`	method chaining (fluent style)

Field vs Parameter

Example

Without this, the statement name = name just assigns the parameter to itself and the field stays null.

public class Main {
    public static void main(String[] args) {
        System.out.println(new Wrong("Asha").name);
        System.out.println(new Right("Asha").name);
    }
}

class Wrong {
    String name;
    Wrong(String name) {
        name = name;          // assigns the parameter to itself
    }
}

class Right {
    String name;
    Right(String name) {
        this.name = name;     // field = parameter
    }
}

Output

null
Asha

Method Chaining with return this

Example

Returning this lets callers chain calls in one expression. Builders in many libraries work this way.

public class Main {
    public static void main(String[] args) {
        Order order = new Order()
                .addItem("Biryani", 250)
                .addItem("Lassi", 60)
                .applyCoupon(50);
        System.out.println("Total: Rs " + order.total);
    }
}

class Order {
    int total;

    Order addItem(String name, int price) {
        System.out.println("Added " + name);
        total += price;
        return this;
    }

    Order applyCoupon(int discount) {
        total -= discount;
        return this;
    }
}

Output

Added Biryani
Added Lassi
Total: Rs 260