Google Dart编程语言学习(1)语法和基本类型

Dart编程语言是一个完全面向对象的语言，包括基础类型如int变量也都是对象。

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));