Class declaration order in java

In general, class declarations can include these components, in order:

• A Java file can contain only one public top-level class.

• Modifiers such as public, private, and a number of others that you will encounter later. (However, note that the private modifier can only be applied to Nested Classes.)

• The class name, with the initial letter capitalized by convention.

• The name of the class's parent (superclass), if any, preceded by the keyword extends. A class can only extend (subclass) one parent.

• A comma-separated list of interfaces implemented by the class, if any, preceded by the keyword implements. A class can implement more than one interface.

• The class body, surrounded by braces, {}.

Example

project/
├── Dog.java
└── Main.java

//Dog.java

// Superclass
class Animal {
    public void eat() {
        System.out.println("Animal is eating...");
    }
}
// Interface 1
interface Pet {
    void play();
}
// Interface 2
interface Trainable {
    void train();
}

// Modifier: public
public class Dog extends Animal implements Pet, Trainable {
    // Fields (attributes)
    private String name;
    private int age;
    // Constructor
    public Dog(String name, int age) {
        this.name = name;
        this.age = age;
    }
    // Method from Pet interface
    @Override
    public void play() {
        System.out.println(name + " is playing fetch!");
    }
    // Method from Trainable interface
    @Override
    public void train() {
        System.out.println(name + " is learning new tricks!");
    }
    // Own method
    public void bark() {
        System.out.println("Woof!");
    }
}

//Main.java

public class Main {
    public static void main(String[] args) {

        Dog dog = new Dog("Buddy", 3);

        dog.eat();
        dog.play();
        dog.train();
        dog.bark();
    }
}