Constructor execution flow in Java - Mini Project: Build & Apply

Constructor Execution Flow in Java

📖 Scenario: Imagine you are creating a simple Java program to understand how constructors work when you create objects. Constructors are special methods that run automatically when you make a new object. This helps set up the object with the right starting values.

🎯 Goal: You will build a Java class with two constructors: one default and one with a parameter. You will see how Java runs these constructors step-by-step when you create objects.

📋 What You'll Learn

Create a class called Car with two constructors

One constructor should have no parameters and print a message

The other constructor should take a String parameter and print a message including the parameter

Create two Car objects: one using the default constructor and one using the parameterized constructor

Print the messages to show the order in which constructors run

💡 Why This Matters

🌍 Real World

Constructors are used in real-world Java programs to set up objects with initial values automatically when they are created.

💼 Career

Understanding constructor execution flow is essential for Java developers to write clean, efficient, and bug-free code when working with classes and objects.

1

Create the Car class with a default constructor

Create a public class called Car. Inside it, write a public constructor with no parameters that prints "Default constructor called".

Java

public class Car {
    // Your code here
}

Need a hint?

Remember, a constructor has the same name as the class and no return type.

2

Add a parameterized constructor to Car

Add a second public constructor to the Car class that takes a String parameter called model. Inside it, print "Parameterized constructor called for model: " followed by the model value.

Java

public class Car {
    public Car() {
        System.out.println("Default constructor called");
    }

    // Your code here
}

Need a hint?

Use + model to add the model name to the printed message.

3

Create two Car objects in Main class

Create a public class called Main with a main method. Inside main, create one Car object using the default constructor and another Car object using the parameterized constructor with the model name "Tesla".

Java

public class Car {
    public Car() {
        System.out.println("Default constructor called");
    }

    public Car(String model) {
        System.out.println("Parameterized constructor called for model: " + model);
    }
}

public class Main {
    public static void main(String[] args) {
        // Your code here
    }
}

Need a hint?

Use new Car() for the default constructor and new Car("Tesla") for the parameterized one.

4

Run the program and print constructor execution messages

Run the Main class. The program should print the messages from both constructors showing the order they run.

Java

public class Car {
    public Car() {
        System.out.println("Default constructor called");
    }

    public Car(String model) {
        System.out.println("Parameterized constructor called for model: " + model);
    }
}

public class Main {
    public static void main(String[] args) {
        Car car1 = new Car();
        Car car2 = new Car("Tesla");
        // Your code here
    }
}

Need a hint?

When you run the program, the messages from both constructors should appear in the console.