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

2024-12-24 10:01:38 +00:00 · 2013-08-11 12:47:21 -04:00 · 2013-08-11 12:47:21 -04:00 · e6bae9cbd3
commit e6bae9cbd3
parent 80ea89b58a 28b26b85ff
8 changed files with 785 additions and 98 deletions
--- a/README.markdown
+++ b/README.markdown
@ -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.

--- a/git.html.markdown
+++ b/git.html.markdown
@ -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
--- a/haskell.html.markdown
+++ b/haskell.html.markdown
@ -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
--- a/python.html.markdown
+++ b/python.html.markdown
@ -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]
--- a/r.html.markdown
+++ b/r.html.markdown
@ -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)

--- a/scala.html.markdown
+++ b/scala.html.markdown
@ -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)

--- a/zh-cn/dart-cn.html.markdown
+++ b/zh-cn/dart-cn.html.markdown
@ -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/
+
+
+