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Ruby ESA 2011/2012 Adam Belloum [email protected] Material Prepared by Eelco Schatborn ES: Ruby •  Today: 1.  Python introducDon 2.  Basic Ruby: types, variables, statements, methods 3.  Regular expression 4.  File and I/O 5.  Modules 6.  Packages 7.  Object Oriented Ruby 8.  DocumentaDon 9.  Examples 10. Assignments IntroducDon to Ruby •  Ruby was created by Yukihiro Matsumoto a.k.a. “Matz” •  Introduced in 1994 •  Officially released by Matsumoto in 1995. •  “Ruby” was named as a gemstone as a joke. . . •  The TIOBE index, which measures the growth of programming languages, ranks Ruby as #9 among programming languages worldwide (2007) “trying to make Ruby natural, not simple,” “Ruby is simple in appearance, but is very complex inside, just like our human body” Matz h^p://www.Dobe.com/index.php/content/paperinfo/tpci/index.html IntroducDon to Ruby •  Ruby is "an interpreted scrip9ng language for quick and easy object-­‐oriented programming" -­‐-­‐ what does this mean? •  interpreted scrip+ng language: –  ability to make operaDng system calls directly –  powerful string opera9ons and regular expressions –  immediate feedback during development h^p://www.rubyist.net/~slagell/ruby/index.html IntroducDon to Ruby •  Ruby is "an interpreted scripDng language for quick and easy object-­‐oriented programming" -­‐-­‐ what does this mean? •  quick and easy: –  variable declaraDons are unnecessary –  variables are not typed –  syntax is simple and consistent –  memory management is automaDc h^p://www.rubyist.net/~slagell/ruby/index.html IntroducDon to Ruby •  Ruby is "an interpreted scripDng language for quick and easy object-­‐oriented programming" -­‐-­‐ what does this mean? •  object oriented programming: –  everything is an object –  classes, methods, inheritance, etc. –  "mixin" funcDonality by module –  iterators and closures (h^p://www.arDma.com/intv/closures.html) h^p://www.rubyist.net/~slagell/ruby/index.html IntroducDon to Ruby •  Ruby is "an interpreted scripDng language for quick and easy object-­‐oriented programming" -­‐-­‐ what does this mean? •  also: –  mulDple precision numbers –  convenient excep9on processing –  dynamic loading –  threading support. h^p://www.rubyist.net/~slagell/ruby/index.html Ruby, Perl and Python •  Design goals –  Expressive like perl but be^er Object-­‐OrientaDon –  Like python but implemenDng true Object-­‐OrientaDon –  No primi9ve types, everything is an object/class –  Fully scriptable Ask an experienced ruby programmer about ruby … •  “What is most amazing about Ruby is a community, they are sharing really a lot. I guess it exploded with github (wriDen in Ruby), at the beginning, github had its own rubygems hosDng. Later, other project appear with its own hosDng and github dropped its rubygems hosDng service and suggested to switch to new one. Now the tool is a official one (rubygems.org).” •  “Also, the same thing is with documenta9on. Every major project hosts its documentaDon but there are many aggregators that are hosDng ruby stdlib and core documentaDon also with documentaDon of many gems -­‐ h^p://ruby-­‐doc.org/ or h^p://rubydoc.info” Git Hub •  GitHub is the best place to share code with friends, co-­‐workers, classmates, and complete strangers. Over two million people use GitHub to build amazing things together. h^p:/github.com/ RubyGems •  A RubyGem is a soEware package, commonly called a “gem”. •  Gems contain a packaged Ruby applica9on or library. •  The RubyGems sojware itself allows you to easily download, install, and manipulate gems on your system h^p://guides.rubygems.org/ Successful story about ruby •  cloud applicaDon plakorm –  deploy and scale powerful apps •  Agile deployment for Ruby and other languages. –  Get up and running in minutes, and deploy instantly with git. Focus 100% on your code, and never think about servers, instances, or VMs again.” •  Run and scale any type of app. –  “Run any web or background process with any web framework or worker type. Scale distributed processes effortlessly with a single command. Easily scale to millions of users.” •  Total visibility across your enDre app. –  View consolidated, real-­‐Dme logging and status from every component of your app and from Heroku itself as it deploys your app, manages your processes, and routes traffic h^p://www.heroku.com Successful story about ruby •  RVM is the Ruby Version Manager. –  It allows to install and manage several different versions and implementaDons of Ruby on one computer, –  including the ability to manage different sets of RubyGems one each. h^p://www.heroku.com Ruby on Rails (RoR) •  Rails is an open source Ruby framework for developing database-­‐backed web applicaDons. •  All layers in Rails are built to work together so you Don’t Repeat Yourself and can use a single language from top to bo^om. •  Everything in Rails is wri^en in Ruby –  Except for configuraDon files -­‐ YAML shows how to create a simple blog webapp in 15 mins. ( of course with experts hands ) h^p://media.rubyonrails.org/video/rails_take2_with_sound.mov 15 How about the issue •  “The worse thing about Ruby itself is a fact that it allow programmer to overload everything. It means that if you do a monkey patching -­‐ if you change one thing like class, module in runDme -­‐ you change them in a whole environment, e.g., if you include a library which changes h^p module from Ruby core, it changes it in a whole environment.” •  Also, the syntax is very tricky, e.g.: foo.bar x is euiqvalent to foo.bar(x) •  but: foo.bar { ... } # passes a block to funcDon foo.bar({ ... }) # passes a hash table to funcDon 16 Ruby Basics •  Normal method for scripDng using #!/usr/bin/ruby
•  irb is an interacDve ruby interpreter –  You can interpret single lines of code –  Good for simple checking and debugging •  You can document Ruby code using the RDoc system –  The documentaDon is inside the source file –  It can be extracted using ri –  To find the documentaDon for a class type ri classname at the command prompt
Simple Example #!/usr/bin/ruby
#helloworld example in Ruby
puts “Hello world”
$ chmod a+x helloWorld.rb
$ helloWorld.rb
Hello world
$
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Python introducDon Basic ruby: types, variables, statements, methods Regular expression File and I/O Modules Packages Object Oriented ruby DocumentaDon Numbers Simple numbers: binary, start with 0b: 0b1100, -­‐0b10001, 0b11111111 . . . decimal: 12, -­‐17, 255 . . . octal, start with 0: 015, -­‐023, 0777 . . . hexadecimal, start with 0x: 0xc, -­‐0x11, 0xff, . . . floaDng point numbers: “one and a quarter ": 1.25 –  scienDfic notaDon: “7.25 Dmes 10 to the 45th power ": 7.25e45. – 
– 
– 
– 
– 
But also matrices and complex numbers using separate modules
Strings (1) •  To create string literals, enclose them in single, or double quotes. •  Examples: 'Hello Class of 2012'
"Ruby is shiny” •  The same type of quote used to start the string must be used to terminate it. •  You can have your own delimiters using %q or %Q %q!"I said 'nuts'", I said!
# %q -­‐à applies the simple quote rules
%Q(It's like a " string,\n \\n is a newline)
# %Q à applies the double quote rules If you use () {} [] as delimiter you can use these
delimiters as a text as long as they are in pairs
Strings (2) •  Escape sequences for single quoted (') strings: only \\ and \’
•  For double quoted (‘”’) strings: \a, \b, \e, \f, \n, \r, \s, \t,
•  You can embed ruby code into a double quoted string using #{. . . }:
"Seconds/day: #{24*60*60}”
à Seconds/day: 86400
Strings (3) •  IntermiDent single and double quoted strings are concatenated to one object: "'Well'" ', he said, ' '"How are you?"’
à 'Well', he said, "How Are You?”
•  You can construct a mulDline string using a “here document”: string = <<END_OF_STRING
The Body of the string is the input
lines up to one ending with the same
text that followed the '<<'
END_OF_STRING
Variables and Constants •  Ruby variables and constants hold references to objects. –  The object decides the type, not the variable –  Reassignment can change the type of the variable •  Naming is as follows: Constants start with a [A-Z], the convenDon is to write all caps with underscores local variables start with a [a-z\_]
global variables start with a `$'
instance variables start with a `@’
class variables start with `@@’
Predefined variables •  Most predefined variables come from perl •  There are predefined variables for: Input/Output ($_, $., …)
Pa^ern Matching ($=, $1 to $9, …)
ExecuDon Environment (Ruby specific) ($0, $”, …)
ExcepDon informaDon ($!, $@)
Standard objects (true, false, ARGV, …)
global Constants (STDIN, STDOUT, …)
http://www.softlab.ntua.gr/facilities/
documentation/unix/ruby-man-1.4/
variable.html#equal
String variables •  String variables are indexed like lists, starDng at 0 •  You can use them using the index operator `[i]'
a = "Hello World"
b = a[4]
# b = o
•  Substrings can be used by pair numbers: `[start,count]' c = a[0,6] # c = "Hello "
d = a[7,4] # d = "orld"
e = a[3,5] # e = "lo Wo”
•  Ranges can also be used to specify indices. Ranges •  Construct ranges of numbers or characters •  Use double dot notaDon for inclusive range creaDon: 1..5 à [1, 2, 3, 4, 5]
•  Use triple dot notaDon for exclusive range creaDon: 1...5 à [1, 2, 3, 4]
Example for string variables: a = "Hello World"
c = a[0..5]
# c = "Hello "
d = a[7..10]
# d = "orld"
e = a[3...9]
# e = ?
Arrays •  Arrays are arbitrary lists of objects •  Create an Array using [ ]: names = [“Fred”,2,"Flintstone”]
•  They too are indexed: a = names[1]
# a is now 2
names[0] = “Wilma”
# names is changed
•  Using a range: names[1..2] à [ 2, "Flintstone" ]
Hashes (1) •  A hash contains objects indexed by keys. •  Any object can be used as a key or value, but . . . •  Create a hash by enclosing `key => value’ combinaDons in curly braces (`{. . . }'): a = { "username" => "xenos",
"home" => "/home/xenos”,
"uid" => 500
}
Hashes (2) •  Access any value using it's key: u = a["username"] # Returns "xenos"
d = a["home"]
# Returns "/home/xenos”
•  To insert or modify objects, you assign a value to a key-­‐
indexed name. a["username"] = "trixie"
a["home"] = "/home/trixie"
a["shell"] = "/usr/bin/tcsh"
Hashes (3) •  Hash membership is tested with several methods: has_key?, has_value?, keys, values a.has_key? "username” # return True
a.has_value? "trixie” # return false
a.keys
# ["xenos", 500, “/usr/bin/tcsh”,
"/home/xenos”]
a.values # ["username", "uid", "shell", "home"]
Expressions •  Single terms are: –  Literals (numbers, strings, arrays, hashes, ranges, symbols, RE's) –  Shell commands, using backquotes: `. . . ` files = `ls *` –  Variable or constant references •  Expression blocks are denoted by begin/do
•  The usual operators: . . . end
+, -, *, /, %, **, !, …
•  Most operators are implemented as methods (may be
overridden) Assignment •  Using parallel assignment in place of using temporary variables: a = 1
b = 2
temp = a
a = b
b = temp
Using parallel assignment: a, b = b, a
ES: Ruby •  Today: 1. 
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Python introducDon Basic Ruby: types, variables, statements, FuncDons Regular expression File and I/O Modules Packages Object Oriented ruby DocumentaDon Comparison Operators == Test for equal value === Comparison operator <=> General comparison operator (returns -­‐1, 0, 1) <, <=, >, >= Normal comparison operators =~ Regular expression match eql? Checks for type and value equality equal? Checks for Object ID equality Flow control •  Code blocks are denoted by { . . . } or do . . . end blocks •  Code blocks can start with an argument list between verDcal bars: |…|
•  #!/usr/bin/ruby presidents = ["Ford", "Carter", "Reagan", "Bush1", "Clinton”] presidents.each {|prez| puts prez} •  Flow control can be exerted using looping or condi9onal statements. Looping Statements (1) •  The standard constructs are present: while condition
until condition
body
body
end
end
•  Using a begin . . . end block the syntax can be reversed: begin
begin
body
end until condition
body
end while condition
Looping Statements (2) •  IteraDng over the members of a sequence containing any type of object. for i in [1,2,"three", 4, 5,'eleven', 7 ]
print i," "
end
•  You can also use a range: for i in 1..10
print i," "
end
Looping Statements (3) •  Most standard object types also provide iterator methods Examples for numbers: 3.times do
print "Hi! "
end
0.upto(93) do
print "Ha! "
end
•  For arrays/files/etcetera there are: obj.each, obj.foreach, . . .
CondiDonal statements (1) •  if and unless statements: if test [ : | then]
unless test [ : | then ]
body
body
elsif test [ : | then ] else
body
body
end
else
body
end
•  You can also use them on expressions as modifiers: expression if test
expression unless test
CondiDonal Statements (2) •  case statement compares each when clause to a target and executes the first match case target
when comparison [: | then]
body
when comparison [: | then]
body
. . .
[else
body ]
end
h^p://ilikestu•log.com/2008/04/15/how-­‐to-­‐write-­‐case-­‐switch-­‐statements-­‐in-­‐ruby/ ES: Ruby •  Today: 1. 
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Python introducDon Basic Ruby: types, variables, statements, Methods Regular expression File and I/O Modules Packages Object Oriented ruby DocumentaDon Methods (1) •  A method can have arguments, è they are passed to the block as an array •  A method will return the result of the last executed expression in the block as the return value •  The return expression will exit the method immediately giving its argument as a return value
Methods (2) •  A simple method definiDon is as follows: def sayhi(name)
print "Hi", name
End
•  A definiDon using pre-­‐ini9alized arguments: def options(a=99, b=a+1)
[ a, b ]
end
options
à[99, 100]
options 1
à[1, 2]
options 2, 4 à[2, 4]
Methods (3) •  super method is a special method for objects –  It executes the funcDon of the same name in the parent object –  to ensure crea9on or ini9aliza9on of parent objects •  super with no arguments –  Ruby sends a message to the parent of the current object, –  to invoke a method of the same name as the method invoking super. –  It automaDcally forwards the arguments that were passed to the method from which it's called. •  super() with an empty argument list –  it sends no arguments to the higher-­‐up method, even if arguments were passed to the current method. •  super(a, b, c) with specific arguments –  it sends exactly those arguments. ES: Ruby •  Today: 1. 
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Python introducDon Basic Ruby: types, variables, statements, methods Regular expression File and I/O Modules Packages Object Oriented ruby DocumentaDon Regular Expressions •  Regular expressions are an object of type Regexp •  They can be created using: / pattern / [options]
%r{ pattern } [options]
Regexp.new(' pattern ' [ , options] )
•  Most standard opDons and pa^erns are available •  For more informaDon see the documentaDon
Regular Expressions •  r1 = Regexp.new('^a-z+:\\s+\w+')
#=> /^a-z+:\s+\w+/
a = "HELLO”
case a
when /^[a-z]*$/; print "Lower case\n”
when /^[A-Z]*$/; print "Upper case\n”
else; print "Mixed case\n”
end
Regular Expressions #!/usr/bin/ruby phone = "2004-­‐959-­‐559 #This is Phone Number" # Delete Ruby-­‐style comments phone = phone.sub!(/#.*$/, "") puts "Phone Num : #{phone}" # Remove anything other than digits phone = phone.gsub!(/\D/, "") puts "Phone Num : #{phone}" ES: Ruby •  Today: 1. 
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Python introducDon Basic Ruby: types, variables, statements, methods Regular expression File and I/O Modules Packages Object Oriented ruby DocumentaDon Opening and Closing Files •  File.new Method aFile = File.new("filename", "mode")
# ... process the file
aFile.close
•  File.open Method File.open("filename", "mode") do |aFile|
# ... process the file
end Reading and WriDng Files •  aFile.gets reads a line from the file object aFile. •  I/O objects provides addiDonal set of access methods
–  sysread: read the contents of a file. –  syswrite : write the contents into a file. –  each_byte: Characters are passed one by one •  The method each_byte is always associated with a block. sysread #!/usr/bin/ruby
aFile = File.new("/var/www/
tutorialspoint/ruby/test", "r")
if aFile
content = aFile.sysread(20)
puts content
else
puts "Unable to open file!"
end syswrite #!/usr/bin/ruby
aFile = File.new("/var/www/
tutorialspoint/ruby/test", "r+")
if aFile
aFile.syswrite("ABCDEF")
else
puts "Unable to open file!"
end each_byte #!/usr/bin/ruby
aFile = File.new("/var/www/
tutorialspoint/ruby/test", "r")
if aFile
aFile.syswrite("ABCDEF")
aFile.each_byte {|ch| putc ch;
putc?. }
else
puts "Unable to open file!"
end •  The class File is a subclass of the class IO. –  IO.readlines –  IO.foreach •  Renaming and DeleDng Files –  File.rename( "test1.txt", "test2.txt" ) –  File.delete("text2.txt") File Inquiries •  File.open("file.rb") if
File::exists?( "file.rb" )
•  File.file?( "text.txt" )
•  File::directory?( "/usr/local/bin" )
•  File.readable?( "test.txt" )
File.writable?( "test.txt” )
•  File.executable?( "test.txt" )
•  File.zero?( "test.txt" )
•  File.size?( "text.txt" )
ES: Ruby •  Today: 1. 
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Python introducDon Basic Ruby: types, variables, statements, FuncDons Regular expression File and I/O Modules Packages Object Oriented ruby DocumentaDon Modules (1) •  Modules are a way of grouping together methods, classes, and constants. Modules give you two major benefits. –  Modules provide a namespace and prevent name clashes. –  Modules implement the mixin facility. •  A Ruby Module is basically a class that cannot be instan9ated •  MulDple modules may be created in a single source file •  Use the definiDons in a module in the same way you would an (instanDated) object •  A redefini9on of a module results in overloading that module Modules (2) •  A module definiDon: CONST = "outer"
module A
CONST = 1
def A.method
CONST + 1
end
end
•  QuesDons: CONST
A::CONST
A.method
à "outer"
à 1
à 2
Modules (3) •  A module definiDon with scope inheritance: CONST = "outer"
module B
def B.method
CONST + "scope"
end
end
•  QuesDon: B.method à "outerscope”
Modules (4) •  Modules can be included in the definiDon of another module or class use: include <module-­‐name> require <modules-name>
•  The including module will have access to all constants, variables, methods etcetera from the included module •  A class may also include a module –  The module will be treated as a superclass for the class –  The module can also contain an ini9alize method Modules (5) module SillyModule
def hello
"Hello."
end
end
class SillyClass
include
SillyModule
End
s = SillyClass.new
Question
s.hello à ”Hello” Including Source files •  Include Ruby source files into a program using load or require
Load
loads the referenced file each Dme it is called Useful for (re)loading source code generated at run-­‐ Dme require loads the referenced file only once. require is a statement, it can be use anywhere statements are allowed For instance from within an if statement. •  Local variables in a loaded file are not propagated to the scope of the loading file ES: Ruby •  Today: 1. 
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Python introducDon Basic Ruby: types, variables, statements, methods Regular expression File and I/O Modules Packages Object Oriented ruby DocumentaDon Classes (1) A ruby class is an extension of the class Class Class names start with a [A-Z]
Classes create a new namespace Classes can be nested, but they will not be made global, so instanDaDon requires the fully qualified classname •  A simple example definiDon: • 
• 
• 
• 
class MyClass
CONST = 12345
def f
'hello world'
end
end Classes (2) •  Create an instance object from a class as follows: obj = MyClass.new
•  The class Class defines a method new which is responsible for the creaDon of an object of the class –  The new method must call the super method to allow the parent class to be allocated, otherwise no objects of that class can be created. •  The class Class also defines the method initialize, which will be invoked in a newly created object, it will receive the arguments passed to new. –  The initialize method must also call super if the parent object is to be properly iniDalized
Classes (3) •  To use a method from an object use a dot notaDon: obj.f
•  To retrieve a constant from an object use the double colon notaDon: obj::CONST
•  Examples: obj.f # hello world
obj::CONST # 12345
Classes (4) Class variables •  class variables are variables shared between all objects of a class class Song
@@plays = 0
def play
@@plays += 1
"This song: Total #@@plays plays."
end
end
Classes (5) Class methods -­‐ object methods vs. class methods -­‐ a class may need to provide methods that work without being Ded to any parDcular object. For example MyClass.new. •  Example class Example
def instMeth
end
def Example.classMeth
end
end
# instance method
# class method
DocumentaDon BOOKS!, they are in the back of the classroom. . . Use the web, there are good websites on ruby Check h^p://www.ruby-­‐lang.org/ for help. h^p://www.ruby-­‐doc.org/docs/ruby-­‐doc-­‐bundle/
index.html •  “Programming Ruby", can be found online via above link • 
• 
• 
• 
Play Around 1.  write a func9on fact to compute factorials. –  The mathemaDcal definiDon of n factorial is: n! = 1 (when n==0) = n * (n-­‐1)! (otherwise) 2.  write a simple ruby prog with case statement where given a model of a car it prints the brand 3.  write a simple ruby prog with arrays, print the element of the array, remove elements, prepend elements –  Hint: Ruby arrays have methods shij, unshij, push, and pop) 4.  write a simple ruby with control statement if. When given democrats it prints the names of democrats presidents in US since 1976, same for republicans Play Around 5.  write a class Decade and a module Week to print the number of weeks in a month, a year, and the number of days in a decade (include the Week module in the Class Decade) –  6.  write a class with runDme Excep9on handling. If the age of a given paDent is bellow a certain age, it generate an excepDon. –  Hints: use raise to generate the exp, and rescue to catch it Play Around 1.  write a func9on fact to compute factorials. –  The mathemaDcal definiDon of n factorial is: n! = 1 (when n==0) = n * (n-­‐1)! (otherwise) # Program to find the factorial of a number
# Save this as fact.rb
def fact(n)
if n == 0
1
else
n * fact(n-1)
end
end
puts fact(ARGV[0].to_i)
Play Around 2.  write a simple ruby prog with case statement where given a model of a car it prints the brand car = "Patriot”
manufacturer = case car
when "Focus": "Ford"
when "Navigator" then "Lincoln"
when "Camry" then "Toyota"
when "Civic" then "Honda"
when "Patriot": "Jeep"
when "Jetta" ; "VW"
when "Ceyene”
"Porsche”
when "520i" then "BMW”
else "Unknown"
end
puts "The " + car + " is made by " + manufacturer
Play Around 3.  write a simple ruby prog with arrays, print the element of the array remove elements, prepend elements –  Hint: Ruby arrays have methods shij, unshij, push, and pop) #!/usr/bin/ruby
presidents = ["Ford", "Carter", "Reagan", "Bush1",
"Clinton", "Bush2"]
presidents.each { |i| print i, "\n"}
#Remove 3 elements from the array
#!/usr/bin/ruby
presidents = ["Ford", "Carter", "Reagan", "Bush1",
"Clinton", "Bush2"]
presidents.pop
presidents.pop
presidents.pop
presidents.each { |i| print i, "\n"}
Play Around 4.  write a simple ruby prog with arrays, print the element of the array, remove elements, and prepend elements –  Hint: Ruby arrays have methods shij, unshij, push, and pop) #!/usr/bin/ruby
presidents = ["Ford", "Carter", "Reagan", "Bush1",
"Clinton", "Bush2"]
presidents.each { |i| print i, "\n"}
#Prepend 3 elements to the array
#!/usr/bin/ruby
presidents = ["Ford", "Carter", "Reagan", "Bush1",
"Clinton", "Bush2”]
presidents.unshift("Nixon")
presidents.unshift("Johnson")
presidents.unshift("Kennedy")
presidents.each { |i| print i, "\n"}
Play Around 5.  write a simple ruby with control statement if. When given democrats it prints the names of democrats presidents in US since 1976, same for republicans #!/usr/bin/ruby
democrats = ["Carter", "Clinton”]
republicans = ["Ford", "Reagan", "Bush1", "Bush2”]
party = ARGV[0]
if party == nil
print "Argument must be \"democrats\" or \"republicans\"\n"
elsif party == "democrats"
democrats.each { |i| print i, " "}
print "\n"
elsif party == "republicans"
republicans.each { |i| print i, " "}
print "\n"
else
print "All presidents since 1976 were either Democrats or
Republicans\n"
Play Around 6.  write a class Decade and a module Week to print the number of weeks in a month, a year, and the number of days in a decade (include the Week module in the Class Decade) #!/usr/bin/ruby
require "Week”
class Decade
include Week
no_of_yrs=10
def no_of_months
puts Week::FIRST_DAY
number=10*12
puts number
end
end
!/usr/bin/ruby
module Week
FIRST_DAY = "Sunday"
def Week.weeks_in_month
puts “four weeks in a month"
end
def Week.weeks_in_year
puts “52 weeks in a year"
end
end
Play Around 7.  write a class Decade and a module Week to print the number of weeks in a month, a year, and the number of days in a decade (include the Week module in the Class Decade) #!/usr/bin/ruby
require "Week”
class Decade
include Week
no_of_yrs=10
def no_of_months
puts Week::FIRST_DAY
number=10*12
puts number
end
end
d1=Decade.new
puts Week::FIRST_DAY
Week.weeks_in_month
Week.weeks_in_year
d1.no_of_months
Play Around 8. 
write a class with runDme Excep9on handling. If the age of a given paDent is bellow a certain age, it generate an excepDon. •  Hints: use raise to generate the exp, and rescue to catch it class MedicareEligibilityException < RuntimeError
def initialize(name, age)
@name = name
@age = age
end
def getName
return @name
end
def getAge
return @age
end
end
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Play Around def writeToDatabase(name, age)
# This is a stub routine
print "Diagnostic: ”,name, ”,age ", age, " is
signed up.\n"
end
def signHimUp(name, age)
if age >= 65 :
writeToDatabase(name, age)
else
myException =
MedicareEligibilityException.new(name, age)
raise myException , "Must be 65 or older for
Medicare", caller
End
end
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Play Around # Main routine
begin
signHimUp("Oliver Oldster", 78)
signHimUp("Billy Boywonder", 18)
signHimUp("Cindy Centurinarian", 100)
signHimUp("Bob Baby", 2)
rescue MedicareEligibilityException => elg
print elg.getName, " is ", elg.getAge, ",
which is too young.\n"
print "You must obtain an exception from
your supervisor. ", elg, "\n”
end
print "This happens after signHimUp was called.\n"
Play Around 9. 
write a simple prog with two classes Mammal and cat the cat Class extends Mammal. •  # class Mammal
def breathe
puts "inhale and exhale"
end
end
class Cat<Mammal
def speak
puts "Meow"
end
end
tama = Cat.new
tama.breathe
tama.speak
Play Around •  write a prog for reduced far for the train (3 Classes Traveler, Student, Honest, both Student and Honest inheritance class Traveler
def identify
puts "I'm a Traveler."
end
def train_toll(age)
if age < 12
puts "Reduced fare.";
else
puts "Normal fare.";
end
end
end
Play Around class Student<Traveler
def identify
puts "I'm a student."
end
end
class Honest<Traveler
def train_toll(age)
super(age) # pass the argument we were given
end
end
Traveler.new.identify
Student1.new.identify
Honest.new.train_toll(25)
Assignment We will be creaDng an Alumni database system. 1. create a class 'alumnus' to store a single person or alumnus in. Create a method for separately adding friends (by reference to an exisDng alumnus object!) 2. test the class by creaDng a group of alumni who are friends. 3. Not all alumni have to be direct friends, you can also have acquaintances. They are friends of your friends that are not your direct friend. So: a distance of 1 is your friend, a distance of 2 is an acquaintance and more than 2 is unknown. Assignment 4. create a class that prints informaDon about a single alumnus 4.1 create a method for prinDng all friends of the alumnus by name 4.2 create a method for prinDng all acquaintances of the alumnus by name 4.3 create a method that prints ALL connected alumni at any distance for the given alumnus. For each connecDon print the distance number, the type of relaDon and the alumni through which they are connected so:2 : acquaintance : eelco -­‐> jarno -­‐> karst implies that eelco knows karst through jarno, meaning jarno is a friend and karst is an acquaintance. Note that there can be mulDple ways that eelco knows karst, always choose the shortest route, and never show a connecDon twice