Dart基础-main及变量、常量、注释

void main() {
  print("hello，world!");
}

print();

//我是单行注释
///我是单行注释 
/*  
我是多行注释
我是多行注释
*/

main(){
  var a="aStr";
  String b="bStr";
  print(a+b);
}

   int num1 = 1;
//  int num2=1.2;
  double num3 = 4;
  double num4 = 4.434343;

 bool isTrue=true;
bool isFalse=false;
 

main(){
  String str1=" abc1 abc";
  String str2='abc2';
  String str3=''' abc3''';
  String str4=r'abc';
  print(str1.hashCode);
  print(str1.isEmpty);
  print(str1.isNotEmpty);
  print(str1.length);
  print(str1.runtimeType);
  print(str1.runes);
  print(str1.toLowerCase());
  print(str1.trim());
  print("str2:${str2}");

void main() {
//  创建list
  var list = [1, 2, 3];
//  添加一个元素
  list.add(4);
//  获取元素长度
  print(list.length);
//  打印元素
  print(list);
//  遍历打印元素
  list.forEach(print);
//  打乱元素
  list.shuffle();
//  打印元素
  print(list);
}

void main(){
//  定义一个map
  Map map={'name':'liyuanjing','age':12};
//  打印name值
  print(map['name']);
//  增加键值address
  map['address']='beijing';
//  删除age键
  map.remove('age');
  print(map);
//  清空map
  map.clear();
  print(map);
}

void main(){
  var name="hello";
  Object name2="hello2";
  dynamic name3="hello3";
  dynamic map={'name':'minos','age':'27'};
//  is判断类型
  var obj1=map is Map<String,String>;
  print(obj1);
//
  var obj2=map as Map<String,String>;
  print(obj2);
}

main() {
  final nums = 300;
  const number = 200;
  print(nums);
  print(number);
}

  const time1='2020-01-01';
//  const time2=DateTime.now();
  final time3='2020-01-01';
  final time4=DateTime.now();
  print(time1);
//  print(time2);
  print(time3);
  print(time4);