Classes and Objects

1 Learn

A class is a blueprint. An object is a real thing built from that blueprint. One class can create many objects.

Each object has its own copy of the fields, so changing one object does not change another.

2 See the Code

Java

class Book {
    String title;
    int pages;

    void show() {
        System.out.println(title + " (" + pages + " pages)");
    }
}

public class Shelf {
    public static void main(String[] args) {
        Book a = new Book();
        a.title = "Code Garden";
        a.pages = 220;

        Book b = new Book();
        b.title = "Object Trails";
        b.pages = 310;

        a.show();
        b.show();
    }
}

Book is one class; a and b are two separate objects.
Each object stores its own title and pages.

Output

Code Garden (220 pages)
Object Trails (310 pages)

3 Practice

Create a Car class with brand and speed, make two Car objects, and print both.

Try it in your own Java setup or write it in the Practice Notebook.

4 Quick Check

1. A class is best described as...
2. Which keyword creates an object?

Step 5

Answer and check the Quick Check above to unlock this.

Day 15