Ruby Language Object-Oriented Programming Concept

Sang Shin, sang.shin@sun.com, www.javapassion.com/rubyonrails

In Ruby, everything is an object. Even a class is an object instance of Class. This has a huge implication in how Ruby works especially in the area of meta-programming.

Expected duration: 120 minutes (excluding homework)

Software Needed

Before you begin, you need to install the JDK and NetBeans IDE software on your computer as described in here.

5513_ruby_object.zip (download)

It contains this document and the lab contents
Download it and unzip in a directory of your choice

OS platforms you can use

Windows
Solaris x86, Solaris Sparc
Linux
Mac OS X

Change Log

July 20th, 2008: Created

Things to be done (By Sang Shin)

Add more detailed explanation to the exercises

Lab Exercises

Exercise 1: The concept of "self" (30 minutes)
Exercise 2: Singleton Method (30 minutes)
Homework Exercise (for people who are taking Sang Shin's "Ruby/JRuby/Rails Development online course")

Exercise 1: The concept of "self"

Learning points

Self objects in different context.

Tasks to be performed

(1.1) Open, build, and run "RubyObject_self_in_TopLevelContext" sample application

1. Open "RubyObject_self_in_TopLevelContext" sample application.

Select File from top-level menu and select Open Project.

Browse down to <LAB_UNZIPPED_DIRECTORY>/ruby_object/samples directory.

Windows: If you unzipped the 5513_ruby_object.zip file under C:\handsonlabs directory under Windows, the directory to which you want to browse down should be C:\handsonlabs\ruby_object\samples.
Linux/Solaris/MacOS: If you unzipped the 5511_ruby_object.zip file under $HOME/handsonlabs directory under Linux, the directory to which you want to browse down should be $HOME/handsonlabs/ruby_object/samples.

Select RubyObject_self_in_TopLevelContext project and click Open Project button.
Observe that the Open Project dialog box appears.
Observe that the main.rb of the RubyObject_self_in_TopLevelContext project is displayed in the editor window.

2. Study the code in main.rb.

puts self
puts self.class

# Top level methods are 'private instance methods of the Object class.
# Because top-level methods are private, you cannot call the with an
# explicit receiver; you can only call them with the default receiver,
# self.
def my_method
puts self
end

my_method

3. Build and run the application.

Right click the project node and select Run. (or press Shift+F6)
Observe the result in the Output window.

4. Spend some time understanding the result.

main
Object
main

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(1.2) Open, build, and run "RubyObject_self_instanceMethod" sample application

1. Open "RubyObject_self_in_InstanceMethod" sample application.
2. Study the code in main.rb.

class MyClass
def my_method
puts self
end
end

my_class = MyClass.new
my_class.my_method #<MyClass:0xae3364>

3. Run the project.
4. Study the result.

#<MyClass:0xae3364>

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(1.3) Open, build, and run "RubyObject_self_in_ClassMethod" sample application

1. Open "RubyObject_self_in_ClassMethod" sample application.
2. Study the code in main.rb.

class MyClass
# Define a class method
def self.my_method
puts self
end
end

MyClass.my_method # MyClass

3. Run the project.
4. Study the result.

MyClass

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(1.4) Open, build, and run "RubyObject_self_in_SingletonMethod" sample application

1. Open "RubyObject_self_in_SingletonMethod" sample application.
2. Study the code in main.rb.

foo = Object.new

# Singleton methods are defined for a particular object. They can be called
# by only the object . When a singleton method is executed, self is the
# object that owns the method.
def foo.bar
puts self
end

# This is another way a singleton method can be defined
class << foo
def bar2
    puts self
end
end

foo.bar         # <Object:0x10ffb38>
foo.bar2       # <Object:0x10ffb38>

3. Run the project.
4. Study the result.

#<Object:0x10ffb38>
#<Object:0x10ffb38>

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(1.5) Open, build, and run "RubyObject_self_in_SingletonMethod2" sample application

1. Open "RubyObject_self_in_SingletonMethod2" sample application.
2. Study the code in main.rb.

class C
end

foo = C.new

# Singleton methods are defined for a particular object. They can be called
# by only the object . When a singleton method is executed, self is the
# object that owns the method.
def foo.bar
puts self
end

foo.bar

# This should display the same object displayed above
puts foo

3. Run the project.
4. Study the result.

#<C:0xb02928>
#<C:0xb02928>

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Exercise 2: Singleton Method

(2.1) Open, build, and run "RubyObject_SingletonMethod" sample application

1. Open "RubyObject_SingletonMethod" sample application.
2. Study the code in main.rb.

foo = Object.new

# Singleton methods are defined for a particular object. They can be called
# by only the object . When a singleton method is executed, self is the
# object that owns the method.
def foo.bar
puts self
end

# This is another way a singleton method can be defined
class << foo
def bar2
    puts self
end
end

foo.bar         #<Object:0x10ffb38>
foo.bar2       #<Object:0x10ffb38>

3. Run the project.
4. Study the result.

#<Object:0x10ffb38>
#<Object:0x10ffb38>

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(2.2) Open, build, and run "RubyObject_SingletonMethod2" sample application

1. Open "RubyObject_SingletonMethod" sample application.
2. Study the code in main.rb.

3. Run the project.
4. Study the result.

#<C:0xb02928>
#<C:0xb02928>

return to top of exercise

Homework Exercise (for people who are taking Sang Shin's "Ruby/JRuby/Rails Development online course")