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Parameterized Constructor in Java

beginner· OOP · Constructors

Problem

A parameterized constructor takes arguments and uses them to set up an object's fields immediately, instead of leaving them at default values until set later.

Create a Car class whose constructor takes a model name and year, and initializes a new object with them directly.

Input

new Car("Mustang", 2023)

Output

Mustang (2023)

Java Program

Java

class Car {
    String model;
    int year;

    Car(String model, int year) {
        this.model = model;
        this.year = year;
    }

    void display() {
        System.out.println(model + " (" + year + ")");
    }
}

public class ParameterizedConstructorDemo {
    public static void main(String[] args) {
        Car car = new Car("Mustang", 2023);
        car.display();
    }
}

▶ Run Code

Output

Mustang (2023)

Core Logic

Passing the model and year straight into the constructor means a Car object is never left half-initialized — both fields are set the moment it's created.

How It Works

1Car(String model, int year) declares a constructor that requires both values up front.
2this.model = model; and this.year = year; assign the constructor's parameters to the object's own fields, using this to distinguish the field from the parameter of the same name.
3new Car("Mustang", 2023) supplies both arguments at the point of creation, running the constructor immediately.
4By the time display() is called, both fields already hold the values passed in — there's no separate setup step needed.

Creating new Car("Mustang", 2023) sets model to "Mustang" and year to 2023 in one step, and display() prints "Mustang (2023)".

💡

Key Point: Unlike a no-argument constructor that would leave model and year at their default values (null and 0), a parameterized constructor forces every caller to supply real values before an object can even exist.

Key Concepts

constructorconstructor argumentsthis keyword

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