那些你不知道的Dart细节之类的点点滴滴（五）

class Point {
  double x;
  double y;
  Point(int x, int y) {
    this.x = x;
    this.y = y;
  }
}

class Point {
  num x;
  num y;
  Point(this.x, this.y);
}

class Point { 
  num x; 
  num y; 
  Point(this.x, this.y); 
  //命名构造函数
  Point.fromJson(Map json) { 
    x = json['x']; 
    y = json['y']; 
  } 
}

class Point { 
  num x; 
  num y; 
  Point(this.x, this.y); 
  //重定向构造函数，使用冒号调用其他构造函数
  Point.alongXAxis(num x) : this(x, 0);
}

import 'dart:math';
class Point {
  //final变量不能被修改，必须被构造函数初始化
  final num x;
  final num y;
  final num distanceFromOrigin;
  //初始化列表
  Point(x, y)
      : x = x,
        y = y,
        distanceFromOrigin = sqrt(x * x + y * y);
}

class Parent {
  int x;
  int y;
  //父类命名构造函数不会传递  
  Parent.fromJson(x, y)
      : x = x,
        y = y {
    print('父类命名构造函数');
  }
}

class Child extends Parent {
  int x;
  int y;
  Child.fromJson(x, y) 
  : x = x,
    y = y,
    print('子类命名构造函数');
  }
}

class Child extends Parent {
  int x;
  int y;
  //若超类没有默认构造函数， 需要手动调用超类其他构造函数
  Child(x, y) : super.fromJson(x, y) {
    //调用父类构造函数的参数无法访问 this
    print('子类构造函数');
  }
}

class Child extends Parent {
  int x;
  int y;
  Child.fromJson(x, y) 
  : x = x,
    y = y,
    super.fromJson(x, y) {
    print('子类命名构造函数');
  }
}

class Point2 {
  //定义const构造函数要确保所有实例变量都是final
  final num x;
  final num y;
  static final Point2 origin = const Point2(0, 0);
  //const关键字放在构造函数名称之前，且不能有函数体
  const Point2(this.x, this.y);
}

class Singleton {
  String name;
  //工厂构造函数无法访问this，所以这里要用static
  static Singleton _cache; 
  //工厂方法构造函数，关键字factory
  factory Singleton([String name = 'singleton']) =>
      Singleton._cache ??= Singleton._newObject(name);
  //定义一个命名构造函数用来生产实例
  Singleton._newObject(this.name);
}

class Rectangle {
  num left;
  num top;
  num width;
  num 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 bottom(num value) => top = value - height;
}

abstract class Demo{
  void zhujiang();
}
class Zhu implements Demo{
  @override
  void zhujiang() {}
}

class Zhu extends Demo{
  @override
  void zhujiang() {}
}

abstract class Demo{
  void zhujiang();
}
abstract class Demo2{
  void zhujiang();
}
abstract class Demo3{
  void zhujiang();
}
class Zhu extends Demo with Demo2,Demo3 implements Demo3,Demo2{
  @override
  void zhujiang() {}
}

class ClassFunction {
  call(String a, String b, String c) => '$a $b $c!';
}
main() {
  var cf = new ClassFunction();
  var out = cf("aaa","flutter","damon");
  print('$out');
  print(cf.runtimeType);
  print(out.runtimeType);
  print(cf is Function);
}

lib/5.dart: Warning: Interpreting this as package URI, 'package:darttest/5.dart'.
aaa flutter damon!
ClassFunction
String
false