1. 变量声明
如何定义变量
var name = 'Bob';
变量的初始值
int lineCount;
assert(lineCount == null); // Variables (even numbers) are initially null.
可以使用var，也可以直接指定类型。
final， 定义为final的变量，值不能够被更改
final name = 'Bob'; // Or: final String name = 'Bob';
name = 'Alice'; // ERROR
2. 基础类型
字符串
字符串可以使用单引号或者双引号。
var s1 = 'Single quotes work well for string literals.';
var s2 = "Double quotes work just as well.";
在字符串中，可以直接应用值， ${表达式}， 如果只是一个变量，就可以去掉{}
var s = 'string interpolation';
assert('Dart has $s, which is very handy.' ==
'Dart has string interpolation, which is very handy.');
assert('That deserves all caps. ${s.toUpperCase()} is very handy!' ==
'That deserves all caps. STRING INTERPOLATION is very handy!');
多行字符串，会被认为默认拼接。
var s = 'String ''concatenation'
" works even over line breaks.";
assert(s == 'String concatenation works even over line breaks.');
如果要使用多行字符串，可以这样, 用'''
var s1 = '''
You can create
multi-line strings like this one.
''';
创建一个不考虑转义的字符串
var s = @"In a raw string, even /n isn't special.";
StringBuffer, 非常类似.net中的。
var sb = new StringBuffer();
sb.add("Use a StringBuffer ");
sb.addAll(["for ", "efficient ", "string ", "creation "]);
sb.add("if you are ").add("building lots of strings.");
var fullString = sb.toString();
数字
主要就2种，int 和 double, 它们都继承num类型
数字和字符串之间的转换
// String -> int
var one = Math.parseInt("1");
assert(one == 1);
// String -> double
var onePointOne = Math.parseDouble("1.1");
assert(onePointOne == 1.1);
// int -> String
var oneAsString = 1.toString();
assert(oneAsString == "1");
// double -> String
var piAsString = 3.14159.toStringAsFixed(2);
assert(piAsString == "3.14");
布尔类型bool，不同于js, 只要不是true, 那么就都是false.
Lists(可以当做数组)
var list = [1,2,3]; //实例化一个list
list.add(4); //添加一个元素4
可以使用for, for...in, foreach()来遍历一个list.
var list = [1,2,3];
for (final x in list) {
print(x);
}
或者
var list = [1,2,3];
list.forEach((element) => print(element));
Maps（字典类型)
var gifts = { // A map literal
// Keys Values
"first" : "partridge",
"second" : "turtledoves",
"fifth" : "golden rings"};
gifts["third"] = "apple"; //添加一个
使用foreach遍历
var gifts = {
"first" : "partridge",
"second": "turtledoves",
"fifth" : "golden rings"};
gifts.forEach((k,v) => print('$k : $v'));
getKeys()和getValues()方法
var gifts = {"first": "partridge", "second": "turtledoves"};
var values = gifts.getValues();
//Print partridge and turtledoves, but not necessarily in that order.
values.forEach((v) => print(v));
