Lesson 2: Two Dogs - Your First Class

Two Dogs Build two objects from one blueprint.

1class Dog {

2 String name;

5public static void main(String[] args) {

6 Dog rex = new Dog();

7 Dog bella = new Dog();

8 rex.name = "Rex";

9 bella.name = "Bella";

10 System.out.println(rex.name);

11 System.out.println(bella.name);

12}

Terminal

$ javac Main.java

$ java Main

Rex

Bella

Every line, explained

class Dog {: class Dog { ... } defines a class: a blueprint describing what every Dog has and can do. A blueprint on its own does nothing; it is a plan, waiting to be built from.
String name;: A variable declared inside a class is called a field. Every Dog built from this blueprint gets its OWN copy: its own little name box.
}: This } closes the class.
public static void main(String[] args) {: The main method: where the program starts, exactly as in Intro to Java.
Dog rex = new Dog();: new Dog() builds a real object from the blueprint. The blueprint is the plan; the object is an actual dog. We store it in a variable of type Dog. First object.
Dog bella = new Dog();: A second new Dog() builds a completely separate object: one blueprint, as many objects as you like, like one house plan and a whole street of houses.
rex.name = "Rex";: The dot reaches inside an object: rex.name means "the name field of the object stored in rex".
bella.name = "Bella";: Each object has its OWN name field; changing bella's name does not touch rex's.
System.out.println(rex.name);: System.out.println(...) prints to the terminal, exactly as in Intro to Java.
System.out.println(bella.name);: System.out.println(...) prints to the terminal, exactly as in Intro to Java. Two objects, two different names.
}: This } closes the main method.