Using Constructors

Lesson 11 of 12 in Coddy's Basics of Classes and Objects in Java course.

When we create an object using the new keyword, we always execute a constructor method (what we learned in the class chapter). By default, every class in Java has an empty constructor, like below:

class MyClass {
	public MyClass() {
	
	}
}

And when we use:

MyClass myObj = new MyClass();

We actually execute this invisible constructor!

As we learned before, let's assume the class:

class Point {
	int x;
	int y;

	public Point(int x, int y) {
		this.x = x;
		this.y = y;
	}
}

Now we can create multiple objects using this constructor, like this:

Point p1 = new Point(5, 3);
Point p2 = new Point(1, 2);
Point p3 = new Point(0, 0);

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Challenge

Easy

You are given a code with a class named Animal, in the main method:

Create an object named cow of type Animal, with type "cow" and voice “Moo”
Create an object named dog of type Animal, with type "dog" and voice “Woof”

Try it yourself

class Animal {
    String type;
    String voice;
    
    public Animal(String type, String voice) {
        this.type = type;
        this.voice = voice;
    }
}

class Main {
    public static void main(String[] args) {
        // Write code here
        
        // Don't change below this line
        System.out.println(cow.type + " is making " + cow.voice);
        System.out.println(dog.type + " is making " + dog.voice);
    }
}

All lessons in Basics of Classes and Objects in Java

1Introduction

Introduction

2Classes

Classes Attributes Methods Constructors Recap challenge #1 Recap challenge #2

3Objects

Create Objects Access Attributes Execute MethodsUsing ConstructorsRecap Challenge #1