07-Function

playground29.dart

Code

void main() {
  showOutput(square(2));
  showOutput(square(2.5));

  print(square.runtimeType);
}

dynamic square(var num) {
  return num * num;
}

void showOutput(var msg) {
  print(msg);
}

Output

4
6.25
(dynamic) => dynamic

playground30.dart

• Arrow Function (=>)
• 箭頭函式 (Arrow functions)

Code

void main() {
  // Arrow Function    =>
  showOutput(square(2));
  showOutput(square(2.5));
}

dynamic square(var num) => num * num;

void showOutput(var msg) {
  print(msg);
}

Output

4
6.25

playground31.dart

Code

main() {
  var list = ['apples', 'bananas', 'oranges'];

  list.forEach(printF);
}

void printF(item) {
  print(item);
}

Output

apples
bananas
oranges

playground32.dart

Code

main() {
  var list = ['apples', 'bananas', 'oranges'];

  list.forEach((item) {
    print(item);
  });
}

Output

apples
bananas
oranges

playground33.dart

Code

void main() {
  print(sum(2, 2));
}

dynamic sum(var num1, var num2) => num1 + num2;

Output

4

playground34.dart

Code

void main() {
  print(sum(num2: 4, num1: 2));
}

dynamic sum({var num1, var num2}) => num1 + num2;

Output

6

playground35.dart

Code

void main() {
  print(sum(10, num2: 2));
}

dynamic sum(var num1, {var num2}) => num1 + num2;

Output

12

playground36.dart

Code

void main() {
  print(sum(10));
  print(sum(10, num2: 2));
}

dynamic sum(var num1, {var num2 = 0}) => num1 + num2;

Output

10
12

08-Class

playground37.dart

Code

class Person {
  String name;
  int age;

  void showOutput() {
    print(name);
    print(age);
  }
}

void main() {
  Person person1 = Person();
  person1.name = 'Mahmud';
  person1.age = 35;
  person1.showOutput();
}

Output

Mahmud
35

playground38.dart

Code

class Person {
  String name;
  int age;

  Person(String name, [int age = 18]) {
    this.name = name;
    this.age = age;
  }

  void showOutput() {
    print(name);
    print(age);
  }
}

void main() {
  Person person1 = Person('Mahmud');
  person1.showOutput();

  Person person2 = Person('Mahmud', 35);
  person2.showOutput();
}

Output

Mahmud
18
Mahmud
35

playground39.dart

Code

class Person {
  String name;
  int age;

  Person(this.name, [this.age = 18]);

  void showOutput() {
    print(name);
    print(age);
  }
}

void main() {
  Person person1 = Person('Mahmud');
  person1.showOutput();

  Person person2 = Person('Mahmud', 35);
  person2.showOutput();
}

Output

Mahmud
18
Mahmud
35

playground40.dart

Code

class Person {
  String name;
  int age;

  Person(this.name, [this.age = 18]);

  // named constructor
  Person.guest() {
    name = 'Guest';
    age = 19;
  }

  void showOutput() {
    print(name);
    print(age);
  }
}

void main() {
  Person person1 = Person('Mahmud');
  person1.showOutput();

  var person2 = Person('Jack', 35);
  person2.showOutput();

  var person3 = Person.guest();
  person3.showOutput();
}

Output

Mahmud
18
Jack
35
Guest
19

playground41.dart

• final: type will be defined by inferred value

Code

class X {
  final name;
  static const int age = 10;

  X(this.name);
}

void main() {
  var x = X('Jack');

  print(x.name);

  print(X.age);

  /* Wrong way
    x.name = 'Jill';
    print(x.name);
  */

  var y = X('Jill');
  print(y.name);
}

Output

Jack
10
Jill

playground42.dart

• 通過 extends 創建 subclasses
• 通過 super 呼叫 parent Object
• Javascript 開發者必須知道的 10 個新功能_medium_peterchang
• super 語法_MDN Web Doc
• 【Java】基本架構：屬性、方法、類別、變數、static_痞客邦_2016
• 物件導向設計：類別與物件_PPT
• ES6 的 Class 、super 的特例與繼承

Code

// Class

class Vehicle {
  String model;
  int year;

  Vehicle(this.model, this.year) {
    print(this.model);
    print(this.year);
  }

  void showOutput() {
    print(model);
    print(year);
  }
}

class Car extends Vehicle {
  double price;

  Car(String model, int year, this.price) : super(model, year);

  void showOutput() {
    print(this.price);
  }
}

void main() {
  var car1 = Car('Accord', 2014, 150000);
  car1.showOutput();
}

Output

Accord
2014
150000.0

playground43.dart

• Define two calculated properties: right and bottom.

Code

class Rectangle {
  num left, top, width, height;

  Rectangle(this.left, this.top, this.width, this.height);

  num get right => left + width;
  set right(num value) => left = value - width;
  num get bottom => top + height;
  set bootom(num value) => top = value - height;
}

void main() {
  var rect = Rectangle(3, 4, 20, 15);
  print(rect.left);
  print(rect.right);
  print(rect.bottom);

  rect.right = 12;
  print(rect.left);
  print(rect.top);

  rect.bootom = 6;
  print(rect.top);
}

Output

3     // left
23    // right = left + width = 3 + 20
19    // bottom = top + height = 4 + 15
-8    // left = value - width = 12 - 20
4     // top = 4
-9    // top = value - height = 6 - 15

09-Exception Handling

playground44.dart

Code

int mustGreaterThanZero(int val) {
  if (val <= 0) {
    throw Exception('Value must be greater than zero');
  }
  return val;
}

void letVerifyTheValue(var val) {
  var valueVerification;

  try {
    valueVerification = mustGreaterThanZero(val);
  } catch (e) {
    print(e);
  } finally {
    if (valueVerification == null) {
      print('Value is not accepted');
    } else {
      print('Value verified: $valueVerification');
    }
  }
}

void main() {
  letVerifyTheValue(10);
  letVerifyTheValue(0);
}

Output

Value verified: 10
Exception: Value must be greater than zero
Value is not accepted