Array of objects

Main class

public class Main {

	public static void main(String[] args) {

//		int[] numbers = new int[3];
//		char[] characters = new char[4];
//		String[] strings = new String[5];
	
//		Food[] refrigerator = new Food[3];
		
		Food food1 = new Food("pizza");
		Food food2 = new Food("hamburger");
		Food food3 = new Food("hotdog");
		
		Food[] refrigerator = {food1, food2, food3};
		
//		refrigerator[0] = food1;
//		refrigerator[1] = food2;
//		refrigerator[2] = food3;
		
		System.out.println(refrigerator[0].name);
		System.out.println(refrigerator[1].name);
		System.out.println(refrigerator[2].name);
	}
}

Food class

public class Food {
	
	String name;
	
	Food(String name){
		this.name =name;
	}
}

Object Passing

Main Class

public class Main {

	public static void main(String[] args) {
		
		Car car1 = new Car("BMW");  
		Car car2 = new Car("Tesla");

		Garage garage = new Garage();
		
		garage.park(car1);
		garage.park(car2);
	}
}

Understanding the flow of Java code, which I still feel I am lacking.
아직 내가 부족한 부분이라고 느끼는 자바 코드의 흐름을 이해하기.

• 1. car1, car2 Instances → “BMW”, “Tesla” ⇒ Car(String name)car1, car2 are instances of the Car class.
     ca1, ca2 인스턴스 → BMW, Tesla의 name을 갖는 Car 클래스의 인스턴스를 생성한다.
• 4. garage is an instance in the Garage class.
• 5. We send the car1, car2 instances that contain “BMW”, “Tesla” to the park() method.
• 6. Then, when the Main Class is executed, the park() method is called.

Car Class

public class Car {
	//Global Variables
	String name;

	//Constructor	
	Car(String name){
		this.name = name;
	}
}

• 2. The Constructor takes a parameter name and assigns its value to the instance variable (String name) ⇒ name using the this keyword.
     Car 클래스는 name 이라는 Global 변수를 가진다. → Car(String name) ⇒ name 변수가 파라미터를 통해 저장된다.

Garage Class

public class Garage {
	void park(Car car) {
		System.out.println("The " + car.name + " is parked in the garage.");
	}
}

• 3. The park() method takes a parameter car in the Car class.
     They're ready to display on the console.
     park() 메소드는 Car 클래스의 car 이라는 오브젝트를 파라미터를 통해 전달받는다.
• 7. Then, they are displayed on the console.
     메소드 내의 기능을 수행한다.

Verify if I have understood correctly.

내가 제대로 이해했는지 검증하기.

I want to display on console “The next song is Vampire by Olivia Rodrigo.”
“The next song is Vampire by Olivia Rodrigo.” 라는 문장을 콘솔에 출력하고 싶다.

public class Main2 {	
	public static void main(String[] args) {

		Musics myFavoriteArtist = new Musics("Vampire", "Olivia Rodrigo");

		Playlist playlist = new Playlist();
		playlist.play(myFavoriteArtist, myFavoriteArtist);
	}
}

public class Musics {
	String music ;
	String artists;
	
	//Constructor
	Musics(String music, String artists){
		this.music = music;
		this.artists = artists;
	}
}

public class Playlist {
	void play(Musics music, Musics artists) {
		System.out.println("The next song is " + music.music
				+ " by  " + artists.artists);			
	}
}

Getter & Setter

public class Main2 {	
	public static void main(String[] args) {
Musics music2 = new Musics();
		System.out.println(music2.getSong());
	
	}
}

public class Musics {

	private String song = "Vampire";
	
	public String getSong() {
		return song;
	}
	public void setSong() {
		this.song = song;
	}
}

Static keyword

public class Main {
	public static void main(String[] args) {
		
		//Static = modifier. A single copy of a variable/method is created and shared. 
		
		Friend friend1 = new Friend("SpiderMan");
		Friend friend2 = new Friend("BatMan");
		Friend friend3 = new Friend("IronMan");

		System.out.println(Friend.numberOfFriends);
		Friend.displayFriends();
	}
}

public class Friend {

	String name;
	static int numberOfFriends;

	Friend(String name){
		this.name = name;
		numberOfFriends++;
	}
	static void displayFriends() {
		System.out.println("You have "+numberOfFriends +" friends");
	}
}

## Output
3
You have 3 friends