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Merge branch 'master' of github.com:adambard/learnxinyminutes-docs

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Camilo Garrido 2013-08-11 12:47:21 -04:00
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5
README.markdown
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@ -16,8 +16,9 @@ properly!
The most requested languages are:
* Scala
* Javascript
* Go
* ~~Scala~~
* ~~Javascript~~
... but there are many more requests to do "every language", so don't let that stop you.

5
git.html.markdown
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@ -310,7 +310,12 @@ Pulls from a repository and merges it with another branch.
# Update your local repo, by merging in new changes
# from the remote "origin" and "master" branch.
# git pull <remote> <branch>
# git pull => implicitly defaults to => git pull origin master
$ git pull origin master
# Merge in changes from remote branch and rebase
# branch commits onto your local repo, like: "git pull <remote> <branch>, git rebase <branch>"
$ git pull origin master --rebase
```
### push

2
haskell.html.markdown
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@ -131,7 +131,7 @@ add 1 2 -- 3
-- with backticks:
1 `add` 2 -- 3
-- You can also define functions that have no characters! This lets
-- You can also define functions that have no letters! This lets
-- you define your own operators! Here's an operator that does
-- integer division
(//) a b = a `div` b

2
python.html.markdown
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@ -6,7 +6,7 @@ filename: learnpython.py
---
Python was created by Guido Van Rossum in the early 90's. It is now one of the most popular
languages in existence. I fell in love with Python for its syntactic clarity. Its basically
languages in existence. I fell in love with Python for its syntactic clarity. It's basically
executable pseudocode.
Feedback would be highly appreciated! You can reach me at [@louiedinh](http://twitter.com/louiedinh) or louiedinh [at] [google's email service]

315
r.html.markdown
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@ -5,7 +5,7 @@ contributors:
filename: learnr.r
---
R is a statistical computing language. It has lots of good built-in functions for uploading and cleaning data sets, running common statistical tests, and making graphs. You can also easily compile it within a LaTeX document.
R is a statistical computing language. It has lots of libraries for uploading and cleaning data sets, running statistical procedures, and making graphs. You can also run `R`commands within a LaTeX document.
```python
@ -14,63 +14,244 @@ R is a statistical computing language. It has lots of good built-in functions fo
# You can't make a multi-line comment per se,
# but you can stack multiple comments like so.
# Hit COMMAND-ENTER to execute a line
# in Windows, hit COMMAND-ENTER to execute a line
###################################################################
# Stuff you can do without understanding anything about programming
###################################################################
data() # Browse pre-loaded data sets
data(rivers) # Lengths of Major North American Rivers
ls() # Notice that "rivers" appears in the workspace
head(rivers) # peek at the dataset
# 735 320 325 392 524 450
length(rivers) # how many rivers were measured?
# 141
summary(rivers)
# Min. 1st Qu. Median Mean 3rd Qu. Max.
# 135.0 310.0 425.0 591.2 680.0 3710.0
stem(rivers) #stem-and-leaf plot (like a histogram)
#
# The decimal point is 2 digit(s) to the right of the |
#
# 0 | 4
# 2 | 011223334555566667778888899900001111223333344455555666688888999
# 4 | 111222333445566779001233344567
# 6 | 000112233578012234468
# 8 | 045790018
# 10 | 04507
# 12 | 1471
# 14 | 56
# 16 | 7
# 18 | 9
# 20 |
# 22 | 25
# 24 | 3
# 26 |
# 28 |
# 30 |
# 32 |
# 34 |
# 36 | 1
stem(log(rivers)) #Notice that the data are neither normal nor log-normal! Take that, Bell Curve fundamentalists.
# The decimal point is 1 digit(s) to the left of the |
#
# 48 | 1
# 50 |
# 52 | 15578
# 54 | 44571222466689
# 56 | 023334677000124455789
# 58 | 00122366666999933445777
# 60 | 122445567800133459
# 62 | 112666799035
# 64 | 00011334581257889
# 66 | 003683579
# 68 | 0019156
# 70 | 079357
# 72 | 89
# 74 | 84
# 76 | 56
# 78 | 4
# 80 |
# 82 | 2
hist(rivers, col="#333333", border="white", breaks=25) #play around with these parameters
hist(log(rivers), col="#333333", border="white", breaks=25) #you'll do more plotting later
#Here's another neat data set that comes pre-loaded. R has tons of these. data()
data(discoveries)
plot(discoveries, col="#333333", lwd=3, xlab="Year", main="Number of important discoveries per year")
plot(discoveries, col="#333333", lwd=3, type = "h", xlab="Year", main="Number of important discoveries per year")
#rather than leaving the default ordering (by year) we could also sort to see what's typical
sort(discoveries)
# [1] 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2
# [26] 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3
# [51] 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4
# [76] 4 4 4 4 5 5 5 5 5 5 5 6 6 6 6 6 6 7 7 7 7 8 9 10 12
stem(discoveries, scale=2)
#
# The decimal point is at the |
#
# 0 | 000000000
# 1 | 000000000000
# 2 | 00000000000000000000000000
# 3 | 00000000000000000000
# 4 | 000000000000
# 5 | 0000000
# 6 | 000000
# 7 | 0000
# 8 | 0
# 9 | 0
# 10 | 0
# 11 |
# 12 | 0
max(discoveries)
# 12
summary(discoveries)
# Min. 1st Qu. Median Mean 3rd Qu. Max.
# 0.0 2.0 3.0 3.1 4.0 12.0
#Basic statistical operations don't require any programming knowledge either
#roll a die a few times
round(runif(7, min=.5, max=6.5))
# 1 4 6 1 4 6 4
#your numbers will differ from mine unless we set the same random.seed(31337)
#draw from a standard Gaussian 9 times
rnorm(9)
# [1] 0.07528471 1.03499859 1.34809556 -0.82356087 0.61638975 -1.88757271
# [7] -0.59975593 0.57629164 1.08455362
#########################
# The absolute basics
# Basic programming stuff
#########################
# NUMBERS
# We've got doubles! Behold the "numeric" class
5 # => [1] 5
class(5) # => [1] "numeric"
# We've also got integers! They look suspiciously similar,
# but indeed are different
5L # => [1] 5
class(5L) # => [1] "integer"
# "numeric" means double-precision floating-point numbers
5 # 5
class(5) # "numeric"
5e4 # 50000 #handy when dealing with large,small,or variable orders of magnitude
6.02e23 # Avogadro's number
1.6e-35 # Planck length
# long-storage integers are written with L
5L # 5
class(5L) # "integer"
# Try ?class for more information on the class() function
# In fact, you can look up the documentation on just about anything with ?
# In fact, you can look up the documentation on `xyz` with ?xyz
# or see the source for `xyz` by evaluating xyz
# Arithmetic
10 + 66 # 76
53.2 - 4 # 49.2
2 * 2.0 # 4
3L / 4 # 0.75
3 %% 2 # 1
# Weird number types
class(NaN) # "numeric"
class(Inf) # "numeric"
class(-Inf) # "numeric" #used in for example integrate( dnorm(x), 3, Inf ) -- which obviates Z-score tables
# but beware, NaN isn't the only weird type...
class(NA) # see below
class(NULL) # NULL
# SIMPLE LISTS
c(6, 8, 7, 5, 3, 0, 9) # 6 8 7 5 3 0 9
c('alef', 'bet', 'gimmel', 'dalet', 'he') # "alef" "bet" "gimmel" "dalet" "he"
c('Z', 'o', 'r', 'o') == "Zoro" # FALSE FALSE FALSE FALSE
#some more nice built-ins
5:15 # 5 6 7 8 9 10 11 12 13 14 15
seq(from=0, to=31337, by=1337)
# [1] 0 1337 2674 4011 5348 6685 8022 9359 10696 12033 13370 14707
# [13] 16044 17381 18718 20055 21392 22729 24066 25403 26740 28077 29414 30751
letters
# [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s"
# [20] "t" "u" "v" "w" "x" "y" "z"
month.abb # "Jan" "Feb" "Mar" "Apr" "May" "Jun" "Jul" "Aug" "Sep" "Oct" "Nov" "Dec"
# Access the n'th element of a list with list.name[n] or sometimes list.name[[n]]
letters[18] # "r"
LETTERS[13] # "M"
month.name[9] # "September"
c(6, 8, 7, 5, 3, 0, 9)[3] # 7
# All the normal operations!
10 + 66 # => [1] 76
53.2 - 4 # => [1] 49.2
2 * 2.0 # => [1] 4
3L / 4 # => [1] 0.75
3 %% 2 # => [1] 1
# Finally, we've got not-a-numbers! They're numerics too
class(NaN) # => [1] "numeric"
# CHARACTERS
# We've (sort of) got strings! Behold the "character" class
"plugh" # => [1] "plugh"
class("plugh") # "character"
# There's no difference between strings and characters in R
"Horatio" # "Horatio"
class("Horatio") # "character"
substr("Fortuna multis dat nimis, nulli satis.", 9, 15) # "multis "
gsub('u', 'ø', "Fortuna multis dat nimis, nulli satis.") # "Fortøna møltis dat nimis, nølli satis."
# LOGICALS
# We've got booleans! Behold the "logical" class
class(TRUE) # => [1] "logical"
class(FALSE) # => [1] "logical"
# booleans
class(TRUE) # "logical"
class(FALSE) # "logical"
# Behavior is normal
TRUE == TRUE # => [1] TRUE
TRUE == FALSE # => [1] FALSE
FALSE != FALSE # => [1] FALSE
FALSE != TRUE # => [1] TRUE
TRUE == TRUE # TRUE
TRUE == FALSE # FALSE
FALSE != FALSE # FALSE
FALSE != TRUE # TRUE
# Missing data (NA) is logical, too
class(NA) # => [1] "logical"
class(NA) # "logical"
# FACTORS
# The factor class is for categorical data
# It has an attribute called levels that describes all the possible categories
factor("dog")
# =>
# [1] dog
# Levels: dog
# (This will make more sense once we start talking about vectors)
# which can be ordered (like childrens' grade levels)
# or unordered (like gender)
levels(factor(c("female", "male", "male", "female", "NA", "female"))) # "female" "male" "NA"
factor(c("female", "female", "male", "NA", "female"))
# female female male NA female
# Levels: female male NA
data(infert) #Infertility after Spontaneous and Induced Abortion
levels(infert$education) # "0-5yrs" "6-11yrs" "12+ yrs"
# VARIABLES
@ -80,8 +261,8 @@ y <- "1" # this is preferred
TRUE -> z # this works but is weird
# We can use coerce variables to different classes
as.numeric(y) # => [1] 1
as.character(x) # => [1] "5"
as.numeric(y) # 1
as.character(x) # "5"
# LOOPS
@ -122,7 +303,7 @@ myFunc <- function(x) {
}
# Called like any other R function:
myFunc(5) # => [1] 19
myFunc(5) # 19
#########################
# Fun with data: vectors, matrices, data frames, and arrays
@ -132,35 +313,35 @@ myFunc(5) # => [1] 19
# You can vectorize anything, so long as all components have the same type
vec <- c(8, 9, 10, 11)
vec # => [1] 8 9 10 11
vec # 8 9 10 11
# The class of a vector is the class of its components
class(vec) # => [1] "numeric"
class(vec) # "numeric"
# If you vectorize items of different classes, weird coercions happen
c(TRUE, 4) # => [1] 1 4
c("dog", TRUE, 4) # => [1] "dog" "TRUE" "4"
c(TRUE, 4) # 1 4
c("dog", TRUE, 4) # "dog" "TRUE" "4"
# We ask for specific components like so (R starts counting from 1)
vec[1] # => [1] 8
vec[1] # 8
# We can also search for the indices of specific components,
which(vec %% 2 == 0) # => [1] 1 3
which(vec %% 2 == 0) # 1 3
# or grab just the first or last entry in the vector
head(vec, 1) # => [1] 8
tail(vec, 1) # => [1] 11
head(vec, 1) # 8
tail(vec, 1) # 11
# If an index "goes over" you'll get NA:
vec[6] # => [1] NA
vec[6] # NA
# You can find the length of your vector with length()
length(vec) # => [1] 4
length(vec) # 4
# You can perform operations on entire vectors or subsets of vectors
vec * 4 # => [1] 16 20 24 28
vec[2:3] * 5 # => [1] 25 30
vec * 4 # 16 20 24 28
vec[2:3] * 5 # 25 30
# and there are many built-in functions to summarize vectors
mean(vec) # => [1] 9.5
var(vec) # => [1] 1.666667
sd(vec) # => [1] 1.290994
max(vec) # => [1] 11
min(vec) # => [1] 8
sum(vec) # => [1] 38
mean(vec) # 9.5
var(vec) # 1.666667
sd(vec) # 1.290994
max(vec) # 11
min(vec) # 8
sum(vec) # 38
# TWO-DIMENSIONAL (ALL ONE CLASS)
@ -175,11 +356,11 @@ mat
# Unlike a vector, the class of a matrix is "matrix", no matter what's in it
class(mat) # => "matrix"
# Ask for the first row
mat[1,] # => [1] 1 4
mat[1,] # 1 4
# Perform operation on the first column
3 * mat[,1] # => [1] 3 6 9
3 * mat[,1] # 3 6 9
# Ask for a specific cell
mat[3,2] # => [1] 6
mat[3,2] # 6
# Transpose the whole matrix
t(mat)
# =>
@ -196,7 +377,7 @@ mat2
# [2,] "2" "cat"
# [3,] "3" "bird"
# [4,] "4" "dog"
class(mat2) # => [1] matrix
class(mat2) # matrix
# Again, note what happened!
# Because matrices must contain entries all of the same class,
# everything got converted to the character class
@ -216,7 +397,7 @@ mat3
# For columns of different classes, use the data frame
dat <- data.frame(c(5,2,1,4), c("dog", "cat", "bird", "dog"))
names(dat) <- c("number", "species") # name the columns
class(dat) # => [1] "data.frame"
class(dat) # "data.frame"
dat
# =>
# number species
@ -224,14 +405,14 @@ dat
# 2 2 cat
# 3 1 bird
# 4 4 dog
class(dat$number) # => [1] "numeric"
class(dat[,2]) # => [1] "factor"
class(dat$number) # "numeric"
class(dat[,2]) # "factor"
# The data.frame() function converts character vectors to factor vectors
# There are many twisty ways to subset data frames, all subtly unalike
dat$number # => [1] 5 2 1 4
dat[,1] # => [1] 5 2 1 4
dat[,"number"] # => [1] 5 2 1 4
dat$number # 5 2 1 4
dat[,1] # 5 2 1 4
dat[,"number"] # 5 2 1 4
# MULTI-DIMENSIONAL (ALL OF ONE CLASS)

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ruby.html.markdown
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@ -275,36 +275,36 @@ surround { puts 'hello world' }
# Define a class with the class keyword
class Human
# A class variable. It is shared by all instances of this class.
@@species = "H. sapiens"
# A class variable. It is shared by all instances of this class.
@@species = "H. sapiens"
# Basic initializer
def initialize(name, age=0)
# Assign the argument to the "name" instance variable for the instance
@name = name
# If no age given, we will fall back to the default in the arguments list.
@age = age
end
# Basic initializer
def initialize(name, age=0)
# Assign the argument to the "name" instance variable for the instance
@name = name
# If no age given, we will fall back to the default in the arguments list.
@age = age
end
# Basic setter method
def name=(name)
@name = name
end
# Basic setter method
def name=(name)
@name = name
end
# Basic getter method
def name
@name
end
# Basic getter method
def name
@name
end
# A class method uses self to distinguish from instance methods.
# It can only be called on the class, not an instance.
def self.say(msg)
puts "#{msg}"
end
# A class method uses self to distinguish from instance methods.
# It can only be called on the class, not an instance.
def self.say(msg)
puts "#{msg}"
end
def species
@@species
end
def species
@@species
end
end

6
scala.html.markdown
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@ -408,9 +408,11 @@ for(line <- Source.fromPath("myfile.txt").getLines())
[Scala for the impatient](http://horstmann.com/scala/)
[Twitter Scala school(http://twitter.github.io/scala_school/)
[Twitter Scala school](http://twitter.github.io/scala_school/)
[The scala documentation]
[The scala documentation](http://docs.scala-lang.org/)
[Try Scala in your browser](http://scalatutorials.com/tour/)
Join the [Scala user group](https://groups.google.com/forum/#!forum/scala-user)

498
zh-cn/dart-cn.html.markdown Normal file
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@ -0,0 +1,498 @@
---
language: dart
filename: learndart.dart
contributors:
- ["Joao Pedrosa", "https://github.com/jpedrosa/"]
translators:
- ["Guokai Han", "https://github.com/hanguokai/"]
---
Dart 是编程语言王国的新人。
它借鉴了许多其他主流语言，并且不会偏离它的兄弟语言 JavaScript 太多。
就像 JavaScript 一样，Dart 的目标是提供良好的浏览器集成。
Dart 最有争议的特性必然是它的可选类型。
```javascript
import "dart:collection";
import "dart:math" as DM;
// 欢迎进入15分钟的 Dart 学习。 http://www.dartlang.org/
// 这是一个可实际执行的向导。你可以用 Dart 运行它
// 或者在线执行! 可以把代码复制/粘贴到这个网站。 http://try.dartlang.org/
// 函数声明和方法声明看起来一样。
// 函数声明可以嵌套。声明使用这种 name() {} 的形式，
// 或者 name() => 单行表达式; 的形式。
// 右箭头的声明形式会隐式地返回表达式的结果。
example1() {
example1nested1() {
example1nested2() => print("Example1 nested 1 nested 2");
example1nested2();
}
example1nested1();
}
// 匿名函数没有函数名。
example2() {
example2nested1(fn) {
fn();
}
example2nested1(() => print("Example2 nested 1"));
}
// 当声明函数类型的参数的时候，声明中可以包含
// 函数参数需要的参数，指定所需的参数名即可。
example3() {
example3nested1(fn(informSomething)) {
fn("Example3 nested 1");
}
example3planB(fn) { // 或者不声明函数参数的参数
fn("Example3 plan B");
}
example3nested1((s) => print(s));
example3planB((s) => print(s));
}
// 函数有可以访问到外层变量的闭包。
var example4Something = "Example4 nested 1";
example4() {
example4nested1(fn(informSomething)) {
fn(example4Something);
}
example4nested1((s) => print(s));
}
// 下面这个包含 sayIt 方法的类声明，同样有一个可以访问外层变量的闭包，
// 就像前面的函数一样。
var example5method = "Example5 sayIt";
class Example5Class {
sayIt() {
print(example5method);
}
}
example5() {
// 创建一个 Example5Class 类的匿名实例，
// 并调用它的 sayIt 方法。
new Example5Class().sayIt();
}
// 类的声明使用这种形式 class name { [classBody] }.
// classBody 中可以包含实例方法和变量，
// 还可以包含类方法和变量。
class Example6Class {
var example6InstanceVariable = "Example6 instance variable";
sayIt() {
print(example6InstanceVariable);
}
}
example6() {
new Example6Class().sayIt();
}
// 类方法和变量使用 static 关键词声明。
class Example7Class {
static var example7ClassVariable = "Example7 class variable";
static sayItFromClass() {
print(example7ClassVariable);
}
sayItFromInstance() {
print(example7ClassVariable);
}
}
example7() {
Example7Class.sayItFromClass();
new Example7Class().sayItFromInstance();
}
// 字面量非常方便，但是对于在函数/方法的外层的字面量有一个限制，
// 类的外层或外面的字面量必需是常量。
// 字符串和数字默认是常量。
// 但是 array 和 map 不是。他们需要用 "const" 声明为常量。
var example8A = const ["Example8 const array"],
example8M = const {"someKey": "Example8 const map"};
example8() {
print(example8A[0]);
print(example8M["someKey"]);
}
// Dart 中的循环使用标准的 for () {} 或 while () {} 的形式，
// 以及更加现代的 for (.. in ..) {} 的形式, 或者
// 以 forEach 开头并具有许多特性支持的函数回调的形式。
var example9A = const ["a", "b"];
example9() {
for (var i = 0; i < example9A.length; i++) {
print("Example9 for loop '${example9A[i]}'");
}
var i = 0;
while (i < example9A.length) {
print("Example9 while loop '${example9A[i]}'");
i++;
}
for (var e in example9A) {
print("Example9 for-in loop '${e}'");
}
example9A.forEach((e) => print("Example9 forEach loop '${e}'"));
}
// 遍历字符串中的每个字符或者提取其子串。
var example10S = "ab";
example10() {
for (var i = 0; i < example10S.length; i++) {
print("Example10 String character loop '${example10S[i]}'");
}
for (var i = 0; i < example10S.length; i++) {
print("Example10 substring loop '${example10S.substring(i, i + 1)}'");
}
}
// 支持两种数字格式 int 和 double 。
example11() {
var i = 1 + 320, d = 3.2 + 0.01;
print("Example11 int ${i}");
print("Example11 double ${d}");
}
// DateTime 提供了日期/时间的算法。
example12() {
var now = new DateTime.now();
print("Example12 now '${now}'");
now = now.add(new Duration(days: 1));
print("Example12 tomorrow '${now}'");
}
// 支持正则表达式。
example13() {
var s1 = "some string", s2 = "some", re = new RegExp("^s.+?g\$");
match(s) {
if (re.hasMatch(s)) {
print("Example13 regexp matches '${s}'");
} else {
print("Example13 regexp doesn't match '${s}'");
}
}
match(s1);
match(s2);
}
// 布尔表达式必需被解析为 true 或 false，
// 因为不支持隐式转换。
example14() {
var v = true;
if (v) {
print("Example14 value is true");
}
v = null;
try {
if (v) {
// 不会执行
} else {
// 不会执行
}
} catch (e) {
print("Example14 null value causes an exception: '${e}'");
}
}
// try/catch/finally 和 throw 语句用于异常处理。
// throw 语句可以使用任何对象作为参数。
example15() {
try {
try {
throw "Some unexpected error.";
} catch (e) {
print("Example15 an exception: '${e}'");
throw e; // Re-throw
}
} catch (e) {
print("Example15 catch exception being re-thrown: '${e}'");
} finally {
print("Example15 Still run finally");
}
}
// 要想有效地动态创建长字符串，
// 应该使用 StringBuffer。 或者 join 一个字符串的数组。
example16() {
var sb = new StringBuffer(), a = ["a", "b", "c", "d"], e;
for (e in a) { sb.write(e); }
print("Example16 dynamic string created with "
"StringBuffer '${sb.toString()}'");
print("Example16 join string array '${a.join()}'");
}
// 字符串连接只需让相邻的字符串字面量挨着，
// 不需要额外的操作符。
example17() {
print("Example17 "
"concatenate "
"strings "
"just like that");
}
// 字符串使用单引号或双引号做分隔符，二者并没有实际的差异。
// 这种灵活性可以很好地避免内容中需要转义分隔符的情况。
// 例如，字符串内容里的 HTML 属性使用了双引号。
example18() {
print('Example18 <a href="etc">'
"Don't can't I'm Etc"
'</a>');
}
// 用三个单引号或三个双引号表示的字符串
// 可以跨越多行，并且包含行分隔符。
example19() {
print('''Example19 <a href="etc">
Example19 Don't can't I'm Etc
Example19 </a>''');
}
// 字符串可以使用 $ 字符插入内容。
// 使用 $ { [expression] } 的形式，表达式的值会被插入到字符串中。
// $ 跟着一个变量名会插入变量的值。
// 如果要在字符串中插入 $ ，可以使用 \$ 的转义形式代替。
example20() {
var s1 = "'\${s}'", s2 = "'\$s'";
print("Example20 \$ interpolation ${s1} or $s2 works.");
}
// 可选类型允许作为 API 的标注，并且可以辅助 IDE，
// 这样 IDE 可以更好地提供重构、自动完成和错误检测功能。
// 目前为止我们还没有声明任何类型，并且程序运行地很好。
// 事实上，类型在运行时会被忽略。
// 类型甚至可以是错的，并且程序依然可以执行，
// 好像和类型完全无关一样。
// 有一个运行时参数可以让程序进入检查模式，它会在运行时检查类型错误。
// 这在开发时很有用，但是由于增加了额外的检查会使程序变慢，
// 因此应该避免在部署时使用。
class Example21 {
List<String> _names;
Example21() {
_names = ["a", "b"];
}
List<String> get names => _names;
set names(List<String> list) {
_names = list;
}
int get length => _names.length;
void add(String name) {
_names.add(name);
}
}
void example21() {
Example21 o = new Example21();
o.add("c");
print("Example21 names '${o.names}' and length '${o.length}'");
o.names = ["d", "e"];
print("Example21 names '${o.names}' and length '${o.length}'");
}
// 类的继承形式是 class name extends AnotherClassName {} 。
class Example22A {
var _name = "Some Name!";
get name => _name;
}
class Example22B extends Example22A {}
example22() {
var o = new Example22B();
print("Example22 class inheritance '${o.name}'");
}
// 类也可以使用 mixin 的形式 ：
// class name extends SomeClass with AnotherClassName {}.
// 必需继承某个类才能 mixin 另一个类。
// 当前 mixin 的模板类不能有构造函数。
// Mixin 主要是用来和辅助的类共享方法的，
// 这样单一继承就不会影响代码复用。
// Mixin 声明在类定义的 "with" 关键词后面。
class Example23A {}
class Example23Utils {
addTwo(n1, n2) {
return n1 + n2;
}
}
class Example23B extends Example23A with Example23Utils {
addThree(n1, n2, n3) {
return addTwo(n1, n2) + n3;
}
}
example23() {
var o = new Example23B(), r1 = o.addThree(1, 2, 3),
r2 = o.addTwo(1, 2);
print("Example23 addThree(1, 2, 3) results in '${r1}'");
print("Example23 addTwo(1, 2) results in '${r2}'");
}
// 类的构造函数名和类名相同，形式为
// SomeClass() : super() {}, 其中 ": super()" 的部分是可选的，
// 它用来传递参数给父类的构造函数。
class Example24A {
var _value;
Example24A({value: "someValue"}) {
_value = value;
}
get value => _value;
}
class Example24B extends Example24A {
Example24B({value: "someOtherValue"}) : super(value: value);
}
example24() {
var o1 = new Example24B(),
o2 = new Example24B(value: "evenMore");
print("Example24 calling super during constructor '${o1.value}'");
print("Example24 calling super during constructor '${o2.value}'");
}
// 对于简单的类，有一种设置构造函数参数的快捷方式。
// 只需要使用 this.parameterName 的前缀，
// 它就会把参数设置为同名的实例变量。
class Example25 {
var value, anotherValue;
Example25({this.value, this.anotherValue});
}
example25() {
var o = new Example25(value: "a", anotherValue: "b");
print("Example25 shortcut for constructor '${o.value}' and "
"'${o.anotherValue}'");
}
// 可以在大括号 {} 中声明命名参数。
// 大括号 {} 中声明的参数的顺序是随意的。
// 在中括号 [] 中声明的参数也是可选的。
example26() {
var _name, _surname, _email;
setConfig1({name, surname}) {
_name = name;
_surname = surname;
}
setConfig2(name, [surname, email]) {
_name = name;
_surname = surname;
_email = email;
}
setConfig1(surname: "Doe", name: "John");
print("Example26 name '${_name}', surname '${_surname}', "
"email '${_email}'");
setConfig2("Mary", "Jane");
print("Example26 name '${_name}', surname '${_surname}', "
"email '${_email}'");
}
// 使用 final 声明的变量只能被设置一次。
// 在类里面，final 实例变量可以通过常量的构造函数参数设置。
class Example27 {
final color1, color2;
// 更灵活一点的方法是在冒号 : 后面设置 final 实例变量。
Example27({this.color1, color2}) : color2 = color2;
}
example27() {
final color = "orange", o = new Example27(color1: "lilac", color2: "white");
print("Example27 color is '${color}'");
print("Example27 color is '${o.color1}' and '${o.color2}'");
}
// 要导入一个库，使用 import "libraryPath" 的形式，或者如果要导入的是
// 核心库使用 import "dart:libraryName" 。还有一个称为 "pub" 的包管理工具，
// 它使用 import "package:packageName" 的约定形式。
// 看下这个文件顶部的 import "dart:collection"; 语句。
// 导入语句必需在其它代码声明之前出现。IterableBase 来自于 dart:collection 。
class Example28 extends IterableBase {
var names;
Example28() {
names = ["a", "b"];
}
get iterator => names.iterator;
}
example28() {
var o = new Example28();
o.forEach((name) => print("Example28 '${name}'"));
}
// 对于控制流语句，我们有：
// * 必需带 break 的标准 switch 语句
// * if-else 和三元操作符 ..?..:..
// * 闭包和匿名函数
// * break, continue 和 return 语句
example29() {
var v = true ? 30 : 60;
switch (v) {
case 30:
print("Example29 switch statement");
break;
}
if (v < 30) {
} else if (v > 30) {
} else {
print("Example29 if-else statement");
}
callItForMe(fn()) {
return fn();
}
rand() {
v = new DM.Random().nextInt(50);
return v;
}
while (true) {
print("Example29 callItForMe(rand) '${callItForMe(rand)}'");
if (v != 30) {
break;
} else {
continue;
}
// 不会到这里。
}
}
// 解析 int，把 double 转成 int，或者使用 ~/ 操作符在除法计算时仅保留整数位。
// 让我们也来场猜数游戏吧。
example30() {
var gn, tooHigh = false,
n, n2 = (2.0).toInt(), top = int.parse("123") ~/ n2, bottom = 0;
top = top ~/ 6;
gn = new DM.Random().nextInt(top + 1); // +1 because nextInt top is exclusive
print("Example30 Guess a number between 0 and ${top}");
guessNumber(i) {
if (n == gn) {
print("Example30 Guessed right! The number is ${gn}");
} else {
tooHigh = n > gn;
print("Example30 Number ${n} is too "
"${tooHigh ? 'high' : 'low'}. Try again");
}
return n == gn;
}
n = (top - bottom) ~/ 2;
while (!guessNumber(n)) {
if (tooHigh) {
top = n - 1;
} else {
bottom = n + 1;
}
n = bottom + ((top - bottom) ~/ 2);
}
}
// 程序的唯一入口点是 main 函数。
// 在程序开始执行 main 函数之前，不期望执行任何外层代码。
// 这样可以帮助程序更快地加载，甚至仅惰性加载程序启动时需要的部分。
main() {
print("Learn Dart in 15 minutes!");
[example1, example2, example3, example4, example5, example6, example7,
example8, example9, example10, example11, example12, example13, example14,
example15, example16, example17, example18, example19, example20,
example21, example22, example23, example24, example25, example26,
example27, example28, example29, example30
].forEach((ef) => ef());
}
```
## 延伸阅读
Dart 有一个综合性网站。它涵盖了 API 参考、入门向导、文章以及更多，
还包括一个有用的在线试用 Dart 页面。
http://www.dartlang.org/
http://try.dartlang.org/