本節課主要4部分內容如下：
Method Missing、More on Strings、Simple Constructs、Ruby Arrays
3.1 Method Missing
在ruby中,如果執行某對象的方法找不到時,則會報NoMethodError
但如果定義了方法method_missing，則錯誤會被該方法攔截
class Dummy
def method_missing(m, *args) #可變參數的定義
puts "There's no method called #{m} here -- please try again."
end
end
Dummy.new.anything
輸出結果:There's no method called anything here -- please try again
3.2 More on Strings
ruby中的string是mutable的,這與java有明顯的不同
1) 常用的不會修改string原始字符串的函數：upcase,downcase,swapcase......
2) 常用的會修改string原始字符串的函數：upcase!,downcase!,swapcase! capitalize!......
注意: 嘆號！在這里的作用,很不可思議吧？
3) 之前我們提到,string可由單引號或雙引號定義,而單引號的效率會更高,
主要原因在于雙引號處理的過程更復雜,過程如下:
a. 查找替換符\,如果找到執行替換操作
b. 查找符號#,如果找到,計算表達式#{expression}
#學習筆記2中有這個例子
注意：對單引號定義的string,則只會處理步驟a
4)String的幾個特殊方法
String.
methods.sort
#列出string class的所有方法，sort用來排序
String.
instance_methods.sort
#列出string instance 的所有方法
String.
instance_methods(false).sort
#列出string中不包括從父類繼承的instance所有方法
5)String的比較
(1)
== #tests two strings for identical content
(2)
String.eql? #tests two strings for identical content
(3)
String.equal? #tests whether two strings are the same object
注意：(1),(2)是比較內容,結果一樣
(3)比較的是引用(是否同一對象)
puts 'test' == 'test' #結果為true
puts 'test'.eql? 'test' #結果為true
puts 'test'.equal?'test' #結果為false
6)
%w的使用
通常定義String的數組時,使用單引號和逗號,
names1 = [ 'ann', 'richard', 'william', 'susan', 'pat' ]
# puts names1[0] # ann
# puts names1[3] # susan
但如果使用%w,可以大大簡化操作
# names2 = %w{ ann richard william susan pat }
# puts names2[0] # ann
# puts names2[3] # susan
3.3 Simple Constructs
1) ruby中,nil和false 被認為是 false 的,其他任何(true,0,....)都是true
2) ruby的簡單結構主要包括
if
end
if
else
end
if
elsif
end
unless
end
while
end
3.4 Ruby Arrays
1) 數組索引從0開始
2) 數組可以動態增加
array = ['Hello', 'Goodbye']
array[2] = 'world'
array[3] = '....'
3)可以使用each獲取數組元素
languages = ['Pune', 'Mumbai', 'Bangalore']
languages.each do |lang|
puts 'I love ' + lang + '!'
end
3.5 總結
* method_missing gives you a way to intercept unanswerable messages and handle them gracefully.
* Refer to the String documentation to use the various methods available.
* For double-quoted string literals, Ruby looks for substitutions - sequences that start with a backslash character - and replaces them with some binary value or does expression interpolation ie. within the string, the sequence #{expression} is replaced by the value of the expression.
* It is to be noted that every time a string literal is used in an assignment or as a parameter, a new String object is created.
* %w is a common usage in strings.
* Observe how one can list all the methods of a class or object.
* Comparing two strings for equality can be done by == or .eql? (for identical content) and .equal? (for identical objects).
* Observe the usage of constructs: if else end, while, if elsif end
* Case Expressions: This form is fairly close to a series of if statements: it lets you list a series of conditions and execute a statement corresponding to the first one that's true. case returns the value of the last expression executed. Usage: case when else end
* Ruby also has a negated form of the if statement, the unless end.
* An Array is just a list of items in order. Every slot in the list acts like a variable: you can see what object a particular slot points to, and you can make it point to a different object. You can make an array by using square brackets.
* Arrays are indexed by integers and the index starts from 0.
* A trailing comma in an array declaration is ignored.
* You can access an array beyond its boundary limits; it will return nil.
* We can add more elements to an existing array.
* Refer the Array documentation for a list of methods.
* The method each (for any object) is an iterator that extracts each element of the array. The method each allows us to do something (whatever we want) to each object the array points to.
* The variable inside the "goalposts" ie. | | refers to each item in the array as it goes through the loop. You can give this any name you want.
* The do and end identify a block of code that will be executed for each item.
3.6 作業
1. Write a Ruby program that asks for a year and then displays to the user whether the year entered by
him/her is a leap year or not.
2. Write a method leap_year. Accept a year value from the user,
check whether it's a leap year and then display the number of minutes in that year.
3. Write a Ruby program that,
when given an array as collection = [1, 2, 3, 4, 5] it calculates the sum of its elements.
4. Write a Ruby program that, when given an array as collection = [12, 23, 456, 123, 4579]
it displays for each number, whether it is odd or even.
5.Write a program that processes a string "Welcome to the forum.\nHere you can learn Ruby.\nAlong with other members.\n" a line at a time, using all that we have learned so far. The expected output is:
# Line 1: Welcome to the forum.
# Line 2: Here you can learn Ruby.
# Line 3: Along with other members.
# 1.Write a Ruby program that asks for a year and then displays to the user
# whether the year entered by him/her is a leap year or not.
def is_leap_year(year)
if (year.to_i % 4==0 && year.to_i % 100!=0) || (year.to_i % 400==0)
return true
end
end
puts 'Please input a year number:'
STDOUT.flush
year = gets.chomp
if is_leap_year(year )
puts "#{year} is a leap year"
else
puts "#{year} is not a leap year"
end
#-----------------------------------------------------
#2 Write a method leap_year. Accept a year value from the user,
# check whether it's a leap year and
# then display the number of minutes in that year.
def is_leap_year(year)
if (year.to_i % 4==0 && year.to_i % 100!=0) || (year.to_i % 400==0)
return true
end
end
puts 'Please input a year number:'
STDOUT.flush
year = gets.chomp
if is_leap_year(year)
puts "#{year} is a leap year"
puts "#{year} has #{366 * 24 *60} minutes"
else
puts "#{year} is not a leap year"
puts "#{year} has #{365 * 24 *60} minutes"
end
#----------------------------------------------
#3 Write a Ruby program that,
# when given an array as collection = [1, 2, 3, 4, 5] it calculates the sum of its elements.
def calculate_sum(array)
sum = 0
array.each do |num|
sum = sum + num
end
return sum
end
puts calculate_sum([1,2,3,4,5])
#----------------------------------------------
#4 Write a Ruby program that, when given an array as collection = [12, 23, 456, 123, 4579]
# it displays for each number, whether it is odd or even.
def display_num_stauts(array)
array.each do |num|
if num % 2 ==0
puts num.to_s + ' is even number'
else
puts num.to_s + ' is odd number'
end
end
end
display_num_stauts([12, 23, 456, 123, 4579])
#----------------------------------------------
#5 Write a program that processes a string s =
# "Welcome to the forum.\nHere you can learn Ruby.\nAlong with other members.\n"
# a line at a time, using all that we have learned so far. The expected output is:
# Line 1: Welcome to the forum.
# Line 2: Here you can learn Ruby.
# Line 3: Along with other members.
s = "Welcome to the forum.\nHere you can learn Ruby.\nAlong with other members.\n"
a = s.split("\n").to_a
a.each do |str|
# puts "Line " + a.index(str).to_s + str
#{a.index(str)} "
puts "Line #{a.index(str)} " + str
end
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本節課主要4部分內容的原文鏈接：