Understanding Dart Language Fundamentals

// Using var
var message = 'Hello, Dart!';
var number = 10;

// Using final
final isFlutter = true;
final version = '3.19';

// Using const
const maxUsers = 1000;
const appName = 'MyApp';

// String operations
String greeting = 'Welcome to ';
String language = 'Dart';
String fullGreeting = greeting + language;

// Numeric operations
int a = 10;
int b = 20;
double sum = a + b; // Implicit conversion to double

// Boolean logic
bool isComplete = true;
bool hasError = false;

// List operations
List<int> numbers = [1, 2, 3];
numbers.add(4);

// Map operations
Map<String, dynamic> user = {
  'name': 'John',
  'age': 30,
};
user['email'] = 'john@example.com';

void main() {
  String? nullableName;
  String nonNullableName = 'Flutter';

  // Safe access with null-aware operator
  print(nullableName ?? 'No name provided');

  // Force non-null value (unsafe)
  print(nonNullableName!);
}

List<String> fruits = ["apple", "banana", "cherry"];
fruits.add("date");
print(fruits[0]); // apple
print(fruits.length); // 4

Map<String, String> person = {
  "name": "John",
  "city": "New York"
};
person["age"] = "30";
print(person["name"]); // John

Set<int> uniqueNumbers = {1, 2, 3, 3, 4};
print(uniqueNumbers); // {1, 2, 3, 4}

int calculate(int a, int b, Function(int, int) operation) {
  return operation(a, b);
}

int add(int x, int y) => x + y;
int multiply(int x, int y) => x * y;

void main() {
  print(calculate(5, 3, add)); // Output: 8
  print(calculate(5, 3, multiply)); // Output: 15
}

String formatName(String firstName, String lastName) => 
    '${firstName.toUpperCase()} ${lastName.toUpperCase()}';

void main() {
  print(formatName('john', 'doe')); // Output: JOHN DOE
}

class Vehicle {<br>  String brand;<br>  int year;<br><br>  Vehicle(this.brand, this.year);<br><br>  void start() {<br>    print('Vehicle started');<br>  }<br>}<br><br>class Car extends Vehicle {<br>  int doors;<br><br>  Car(String brand, int year, this.doors) : super(brand, year);<br><br>  void openTrunk() {<br>    print('Trunk opened');<br>  }<br>}<br><br>void main() {<br>  Car myCar = Car('Toyota', 2023, 4);<br>  myCar.start();<br>  myCar.openTrunk();<br>}<br>

class Student {
  String name;
  int grade;

  Student(this.name, this.grade);

  Student.highSchool(String name) : this(name, 12);

  Student.college(String name) : this(name, 16);
}

void main() {
  var highSchoolStudent = Student.highSchool("Alice");
  var collegeStudent = Student.college("Bob");

  print(highSchoolStudent.name); // Alice
  print(collegeStudent.name); // Bob
}

abstract class Animal {
  String sound();
}

class Dog extends Animal {
  @override
  String sound() => "Woof!";
}

class Cat extends Animal {
  @override
  String sound() => "Meow!";
}

class AnimalFactory {
  static Animal createAnimal(String type) {
    if (type == "dog") {
      return Dog();
    } else if (type == "cat") {
      return Cat();
    } else {
      throw Exception("Unknown animal type");
    }
  }
}

void main() {
  var dog = AnimalFactory.createAnimal("dog");
  print(dog.sound()); // Woof!
}

// Define a mixin
mixin Logger {
  void log(String message) {
    print('Log: $message');
  }
}

// Use the mixin in a class
class MyClass with Logger {
  void doSomething() {
    log('Doing something...');
  }
}

// Example usage
void main() {
  var obj = MyClass();
  obj.doSomething(); // Output: Log: Doing something...
}

// Define an extension on String
extension StringExtensions on String {
  bool get isEmail {
    return contains('@') && contains('.');
  }

  String capitalize() {
    if (isEmpty) return this;
    return '${this[0].toUpperCase()}${substring(1).toLowerCase()}';
  }
}

// Example usage
void main() {
  String email = 'user@example.com';
  print(email.isEmail); // true

  String name = 'john doe';
  print(name.capitalize()); // John doe
}

Future<String> fetchUserData() async {
  await Future.delayed(Duration(seconds: 2));
  return 'User data';
}

void main() async {
  String userData = await fetchUserData();
  print(userData); // Prints 'User data' after 2 seconds
}

Future<String> fetchName() async {
  await Future.delayed(Duration(milliseconds: 500));
  return 'John';
}

Future<String> fetchEmail() async {
  await Future.delayed(Duration(milliseconds: 300));
  return 'john@example.com';
}

void main() async {
  String name = await fetchName();
  String email = await fetchEmail();
  print('Name: $name, Email: $email');
}

Stream<int> numberStream = Stream.fromIterable([1, 2, 3, 4, 5]);

numberStream.listen((value) {
  print('Received: $value');
});

Future<String> fetchUserData() async {
  await Future.delayed(Duration(seconds: 2));
  return 'John Doe';
}

void main() async {
  String name = await fetchUserData();
  print(name);
}

Stream<int> errorStream = Stream<int>.error(Exception('Something went wrong'));

errorStream.handleError((error) {
  print('Error occurred: $error');
});

final button = RaisedButton(
  onPressed: () {},
  child: Text("Click me"),
)..backgroundColor = Colors.blue
..textColor = Colors.white;

final fruits = ["apple", "banana"];
final moreFruits = ["orange", "grape"];
final allFruits = [...fruits, ...moreFruits]; // ["apple", "banana", "orange", "grape"]