double d = 1 / 3;
System.out.print(d);

// помещает элемент в стек.
void push(E e);

// извлекает элемент из стека.
E pop();

java -jar app.jar < file.txt

public enum Vehicle { CAR, BUS, BICYCLE, SCOOTER }

public enum Animal {
    DOG("black"),
    CAT("white"),
    RAT("gray");

    private final String color;
    Animal(String color){
        this.color = color;
    }
    public String getColor(){
        return color;
    }
}

public class Main {
    public static void main(String[] args) {
        for (Animal a : Animal.values()) {
            System.out.println(a.name() + " - " + a.getColor());
        }
    }
}

DOG - black
CAT - white
RAT - gray

public enum Operation {
   PLUS { double evaluate(double x, double y) { return x + y; } },
   MINUS  { double evaluate(double x, double y) { return x - y; } },
   abstract double evaluate(double x, double y);
}

JSONObject author = new JSONObject();
author.put("name", "J. K. Rowling");
author.put("numberOfBooks", 22);

JSONArray books = new JSONArray();
books.put("Harry Potter and the Philosopher's Stone");
books.put("Harry Potter and the Chamber of Secrets");
books.put("Harry Potter and the Prisoner of Azkaban");

author.put("books", books);
System.out.print(author);

{"books":["Harry Potter and the Philosopher's Stone","Harry Potter and the Chamber of Secrets","Harry Potter and the Prisoner of Azkaban"],"name":"J. K. Rowling","numberOfBooks":22}

JSONObject author = new JSONObject(serializedString);
System.out.println("name: " + author.get("name"));
System.out.println("numberOfBooks: " + author.get("numberOfBooks"));

JSONArray books = (JSONArray) author.get("books");
Iterator<Object> i = books.iterator();
System.out.println("books:");
while (i.hasNext()) {
    System.out.println(i.next());
}

<dependency>
 <groupId>org.json</groupId>
 <artifactId>json</artifactId>
 <version>20231013</version>
</dependency>

import java.util.ArrayList;

public class arrayVsArrayList {

  public static void main(String[] args) {

    // объявление Array
    int[] myArray = new int[6];

    // обращение к несуществующему индексу
    myArray[7]= 10; // ArrayIndexOutOfBoundsException

    // объявление ArrayList
    ArrayList<Integer> myArrayList = new ArrayList<>();

    // простое добавление и удаление элементов
    myArrayList.add(1);
    myArrayList.add(2);
    myArrayList.add(3);
    myArrayList.add(4);
    myArrayList.add(5);
    myArrayList.remove(0);

    // получение элементов ArrayList    
    for(int i = 0; i < myArrayList.size(); i++) {
      System.out.println("Element: " + myArrayList.get(i));
    }
  
    // многомерный Array
      int[][][] multiArray = new int [3][3][3]; 
    }
}