Fundamentals of Dart

main.dart

// INHERITANCE

// void main() {
//   Lizard liz = Lizard();
// //    Cat kitty = Cat();
// //    kitty.test();

//   liz.test(); // Testing in Lizard, Animal, and Reptile
//   liz.crawl(); // Now we can call crawl() from Reptile class
// }

// class Animal {
//   void test() => print("Testing in Animal");
// }

// class Reptile {
//   bool canCrawl = true;
//   void crawl() => print("Crawl");
//   void test() => print("Testing in Reptile");
// }

// class Cat extends Animal {
//   bool hasTwoPointyEars = true;
//   void meow() => print("Meow!!");

//   @override
//   void test() {
//     print("Testing in Cat");
//     super.test();
//   }
// }

// class Lizard extends Animal with Reptile {
//   bool hasTail = true;
//   @override
//   void test() {
//     print("Testing in Lizard");
//     super.test();
//   }
// }

// INTERFACES

// void main(){
//    Manager srd = new Manager();
//    srd.printSomething();
// }
// class Worker {
//     String name = "";
//     void printSomething() => print("Worker Printing");
// }
// class Manager implements Worker {
//     String name = "Sharad";
//     void printSomething() => print("Manager Printing");
// }

// ABSTRACTION

// void main() {
//   var rect = Rectangle();
//   rect.draw();
// }

// abstract class Shape {
//   String x; // Can also define instance variable
//   void draw(); // abstract method
//   // We can also define normal functions as well
// }

// // Whenever we extend a abstract class, then its mendatory to override that class's abstract methods
// class Rectangle extends Shape {
//   String x = "yo!";
//   void draw() =>   print("Overrided!!");
// }

// GENERICS

// void main(){
//    add<int>(1, 2); // prints 3
//    add<double>(1.0, 2.0); // prints 3.0
//    add<String>("Sharad", "Ghimire"); // prints SharadGhimire
//    //addNumbers<String>("a", "b"); // Gives error but still work??
//  }
// void add<T>(T a, T b) {   // T is shorthand for type
//     print(a + b); // But, for String, the operator + isn't defined for the class 'Object'
// }
// void addNumbers<T extends num>(T a, T b){ // num includes int and doubles so it does not work for String
//     print(a +b);
// }

// void main() {
//   var studentName = "John Doe";
//   print(studentName?.toUpperCase());
// }

// String printRoll() {
//   //int rollNo = 52;
//   print("The roll number alloted to you is : $rollNo.toString()");
// }

/// EXCEPTION HANDLING

// CASE 1 - when the exception is known
// void main() {

// //     int result = 12~/0;
// //   	print("The answer is: $result");

// //     on IntegerDivisionByZero {
// //     print("Cannot divide by zero");
// //   }

// print(" ");

// // CASE 2: When the specific exception is not known
// 	try {
//     int result = 12~/0;
//     print(" The result is $result");
//   } catch(e) {
//     print("The exception raised is $e");
//   }

//   print("");

// //   CASE 3: When the stack trace needs to be printed
//   try {
//     int result = 24~/0;
//     print("Result: $result");
//   } catch(e,s) {
//     print("Exception raised is $e and the stack trace is \n $s");
//   }

//   print("");

// //   CASE 4 : Whether or not an exception is thrown execute the FINALLY clause
//   try {
//     int result = 24~/12;
//     print("Result: $result");
//   } catch(e) {
//     print("Exception raised is $e");
//   } finally {
//     print("FINALLY clause executed");
//   }

//   print(" ");

// //   CASE 5: Custom exception handling
//  	try {
//     amountDeposit(-200);
//   } catch(e){
//     print(e.errorMessage());
//   }

// }

// class DepositException implements Exception {
//     String errorMessage() {
//       return "Cannot enter amount less than 0";
//     }
//   }

// void amountDeposit(int amount) {
// //     int amount = -100;
//     if(amount < 0) {
//       throw DepositException();
//     }
//   }

// class Person {
//   DateTime birthday;
//   String name;
//   final int DAYS = 365;

//   Person(this.name, {this.birthday});

//   void set age(double years) {
//     var d = new DateTime.now();
//     var dur = new Duration(days: (DAYS*years).toInt());
//     d = d.subtract(dur);
//     birthday = d;
//   }

//   double get age {
//     var d = new DateTime.now();
//     return d.difference(birthday).inDays / DAYS;
//   }

//   double myage() {
//     var d = new DateTime.now();
//     return d.difference(birthday).inDays / DAYS;
//   }
// }

// main() {
//   var p = new Person("Foo");
//   print(p.name);
//   p.age = 18.0;
//   print(p.age);

//   print(p.myage()); // () required because it is not a real getter

//   var o = new Person("Bar", birthday: DateTime.parse("19900212"));
//   print(o.name);
//   print(o.birthday);
//   print("${o.age} is the age in years");
// }

// HIGHER ORDER FUNCTIONS

// accepts a function as a parameter OR returns a function
void main() {
//  calling the higher order function
  Function addNum = (int a, int b) => print(a + b);
  helloMessage("Hello", addNum);

  var squaredNumber = squareNum();
  print(squaredNumber(10));
}

// Case 1 : higher order function, with function as a parameter
void helloMessage(String message, Function myFunc) {
//   print("FUNCTION");
  print("$message,");
  myFunc(3, 7);
}

// Case 2 : higher order function which returns a function
Function squareNum() {
  Function square = (int number) => number * number;
  return square;
}