DESIGN PATTERNS

// Singleton Pattern
class Database {
    private static Database instance;
    
    private Database() {} // private constructor
    
    public static Database getInstance() {
        if (instance == null) {
            instance = new Database();
        }
        return instance;
    }
    
    public void query(String sql) {
        System.out.println("Executing: " + sql);
    }
}

public class Main {
    public static void main(String[] args) {
        Database db = Database.getInstance();
        db.query("SELECT * FROM users");
    }
}