Continue with the Basics by Example; today's version of the post written in JRuby Enjoy!
You can copy and paste the code below in your favorite IDE/Editor and start playing and learning with it. This little "working" program will teach you the basics of the Programming Language.
There are some "comments" on the code added just to tell you what are or how are some features called. In case you want to review the theory, you can read my previous post, where I give a definition of each of the concepts mentioned on the code. You can find it here: http://carlosqt.blogspot.com/2010/08/new-series-languages-basics-by-example.html
Greetings Program - Verbose
# JRuby basics
require "java"
import java.util.GregorianCalendar
import java.util.Calendar
import java.lang.System
module RbGreetProgram
class Greet
# Fields or Attributes
@message = ""
@name = ""
@loopMessage = 0
# Properties | Getters, Setters
def message
@message
end
def message=(val)
@message = capitalize(val)
end
def name
@name
end
def name=(val)
@name = capitalize(val)
end
def loopMessage
@loopMessage
end
def loopMessage=(val)
@loopMessage = val
end
# Constructor or Initializer Method
def initialize
@message = ""
@name = ""
@loopMessage = 0
end
# Overloaded Constructor
# No Overloaded Constructors/Initializers Support in Ruby
# Method 1
def capitalize(val)
# "if-then-else" statement
if val.length >= 1
return val.capitalize
else
return ""
end
end
private :capitalize
# Method 2
def salute
# "for" statement
for i in 0..@loopMessage
puts "#@message #@name!"
end
end
# Overloaded Method
# No Overloaded Methods Support in Ruby. New methods instead.
# Method 2.1
def salute21(message, name, loopMessage)
# "while" statement
i = 0
while i < loopMessage do
puts "#{capitalize(message)} #{capitalize(name)}!"
i += 1
end
end
# Method 2.2
def salute22(name)
# "switch/case" statement
dtNow = GregorianCalendar.new
@message = case dtNow.get(Calendar::HOUR_OF_DAY)
when 6..11 then "good morning,"
when 12..17 then "good afternoon,"
when 18..22 then "good evening,"
when 23,0..5 then "good night,"
else "huh?"
end
puts "#{capitalize(@message)} #{capitalize(name)}!"
end
end
# Console Program
# Define variable object of type Greet
# Instantiate Greet. Call Constructor
g = Greet.new
# Call Set Properties
g.message = "hello"
g.name = "world"
g.loopMessage = 5
# Call Method 2
g.salute()
# Call Method 2.1 and Get Properties
g.salute21(g.message, "jRuby", g.loopMessage)
# Call Method 2.2
g.salute22("carlos")
# Stop and exit
puts "Press any key to exit..."
gets
end
Greetings Program - Minimal
# JRuby basics
require "java"
import java.util.GregorianCalendar
import java.util.Calendar
import java.lang.System
class Greet
# Fields or Attributes
@message = ""
@name = ""
@loopMessage = 0
# Properties | Getters, Setters
def message
@message
end
def message=(val)
@message = capitalize(val)
end
def name
@name
end
def name=(val)
@name = capitalize(val)
end
def loopMessage
@loopMessage
end
def loopMessage=(val)
@loopMessage = val
end
# Constructor or Initializer Method
def initialize
@message = ""
@name = ""
@loopMessage = 0
end
# Overloaded Constructor
# No Overloaded Constructors/Initializers Support in Ruby
# Method 1
def capitalize(val)
# "if-then-else" statement
if val.length >= 1
return val.capitalize
else
return ""
end
end
private :capitalize
# Method 2
def salute
# "for" statement
for i in 0..@loopMessage
puts "#@message #@name!"
end
end
# Overloaded Method
# No Overloaded Methods Support in Ruby. New methods instead.
# Method 2.1
def salute21(message, name, loopMessage)
# "while" statement
i = 0
while i < loopMessage do
puts "#{capitalize(message)} #{capitalize(name)}!"
i += 1
end
end
# Method 2.2
def salute22(name)
# "switch/case" statement
dtNow = GregorianCalendar.new
@message = case dtNow.get(Calendar::HOUR_OF_DAY)
when 6..11 then "good morning,"
when 12..17 then "good afternoon,"
when 18..22 then "good evening,"
when 23,0..5 then "good night,"
else "huh?"
end
puts "#{capitalize(@message)} #{capitalize(name)}!"
end
end
# Console Program
# Define variable object of type Greet
# Instantiate Greet. Call Constructor
g = Greet.new
# Call Set Properties
g.message = "hello"
g.name = "world"
g.loopMessage = 5
# Call Method 2
g.salute()
# Call Method 2.1 and Get Properties
g.salute21(g.message, "jRuby", g.loopMessage)
# Call Method 2.2
g.salute22("carlos")
# Stop and exit
puts "Press any key to exit..."
gets
And the Output is:
Where to define Class Fields/Attributes in JRuby
puts "Class Attributes Example:"
class ClassAttributes
# You do not need to explicitly add the Fields/Attributes as shown below within the class:
# message = ""
# name = ""
# loopMessage = 0
# because they are added to the class as Fields/Attributes the first time they appear in
# your code. For example, here below, in the Initialize method,
# we have 2 fields (name and message)
def initialize
@message = "message" # class field
@name = "name" # class field
end
# and one more within a public method (loopMessage)
def salute
@loopMessage = 1 # class field
localtest = 0 # local variable
puts "#@message, #@name, #@loopMessage"
end
end
# Then, you can access each of them as you normally do:
f = ClassAttributes.new
f.salute
Auto-Implemented Properties in JRuby
Auto-implemented properties enable you to quickly specify a property of a class without having to write code to Get and Set the property. The following code shows how to use them just like with VB.NET, C#, C++/CLI and so on.
puts ""
puts "Auto-Implemented Properties Example:"
# Ruby basics
class Greet
# Fields or Attributes
#@message = ""
# Manual Properties | Getters, Setters
#def message
# @message
#end
#def message=(val)
# @message = capitalize(val)
#end
# Instead of creating a field and a manual property (as above)
# we use the attributes syntax to create our Auto-Implemented Property
# that will be linked to our @message class field/attribute
attr_accessor :message
# you can also create read or write only props using attr_writer|attr_reader
def initialize
@message = ""
end
def salute
puts "#@message"
end
end
g = Greet.new
# we set the value of message through our write property
g.message = "hello ruby"
g.salute
# or get the value from it as well
puts g.message
Overloading Constructor and Methods in JRuby
Ruby does not support Overloading Methods nor Constructors, instead, you can define one method with variable arguments and code the if-elseif code to handle both(or multiple) cases yourself.
puts ""
puts "Overloaded-like Constructor and Method Example:"
class Overloading
# Constructor with variable arguments
def initialize(*args)
# if args list/sequence is not empty we use the arguments,
# otherwise we use the class fields
if args.size > 0
@message = args[0]
@name = args[1]
@loopMessage = args[2]
else
@message = 'empty_message'
@name = 'empty_name'
@loopMessage = 2
end
end
# Method with variable arguments
def salute(*args)
# if args list/sequence is not empty we use the arguments,
# otherwise we use the class fields
if args.size > 0
for i in 1..args[2]
puts "#{args[0]}, #{args[1]}!"
end
else
for i in 1..@loopMessage
puts "#@message, #@name!"
end
end
end
end
# and now we use the "overloaded-like" constructor and method
# calling constructor without parameters
o1 = Overloading.new
# calling method without parameters
o1.salute
# calling method with parameters
o1.salute("Hello", "JRuby", 3)
# calling constructor with with parameters
o2 = Overloading.new("Hello", "Carlos", 2)
# calling method without parameters
o2.salute
And the Output is:
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