Ruby 简明教程高级进阶 Part 1

时间 2020-06-09 标签 ruby 简明教程高级进阶

Ruby 简明教程

高级进阶

1. Ruby - Object Oriented 面向对象

Ruby 是纯粹面向对象的语言。Ruby将每一个事物都看做对象，甚至原始的类型，字符串，数值， true/false. ruby

本节介绍与面向对象有关的主要功能。ide

类是来指定对象的形式，包含数据和方法。类内的数据和方法，被称做成员。this

1.1Ruby Class Definition

定义类的时候，定义类的蓝本，即类对象包含什么已经能够对对象作什么操做。scala

关键词 class开头， 跟着类名 class name， 最后以 end结束. code

class Box
   code
end

类名必须以大写字母开头。习惯上用驼峰式命名(CamelCase).

1.2 Define Ruby Objects

建立新的对象，用关键词neworm

box1 = Box.new
box2 = Box.new

1.3 The initialize Method

initialize method 初始化方法 是标准类方法，和其它面向对象的语言的构造器constructor 相似。初始化方法能够在对象建立时初始化类变量。对象

class Box
   def initialize(w,h)
      @width, @height = w, h
   end
end

1.4 The instance Variables

instance variables 实例变量是类属性，当用类来建立对象时变成对象特性。每一个对象的属性单独赋值，各个对象不共享。类内用@访问，类外用公共方法accessor 访问。继承

class Box
   def initialize(w,h)
      # assign instance variables
      @width, @height = w, h
   end
end

1.5 The accessor & setter Methods

要在类外访问类变量，必须在accessor methods内定义。,accessor method 又叫 getter methods.教程

demo_accessor.rbip

# define a class
class Box
   # constructor method
   def initialize(w,h)
      @width, @height = w, h
   end

   # accessor methods
   def printWidth
      @width
   end

   def printHeight
      @height
   end
end

# create an object
box = Box.new(10, 20)

# use accessor methods
x = box.printWidth()
y = box.printHeight()

puts "Width of the box is : #{x}"
puts "Height of the box is : #{y}"

执行结果：

zzl@zzl-VirtualBox:~/rubyprojects$ ruby demo_accessor.rb
Width of the box is : 10
Height of the box is : 20

同 accessor methods相似，从类外部设置类变量，使用setter methods

# define a class
class Box
   # constructor method
   def initialize(w,h)
      @width, @height = w, h
   end

   # accessor methods
   def getWidth
      @width
   end
   def getHeight
      @height
   end

   # setter methods
   def setWidth=(value)
      @width = value
   end
   def setHeight=(value)
      @height = value
   end
end

# create an object
box = Box.new(10, 20)

# use setter methods
box.setWidth = 30
box.setHeight = 50

# use accessor methods
x = box.getWidth()
y = box.getHeight()

puts "Width of the box is : #{x}"
puts "Height of the box is : #{y}"

执行结果

zzl@zzl-VirtualBox:~/rubyprojects$ ruby demo_setter.rb
Width of the box is : 30
Height of the box is : 50

1.6 The instance Methods

instance methods 实例方法和其它方法同样用def 定义，能够使用类实例。

# define a class
class Box
   # constructor method
   def initialize(w,h)
      @width, @height = w, h
   end
   # instance method
   def getArea
      @width * @height
   end
end

# create an object
box = Box.new(10, 20)

# call instance methods
a = box.getArea()
puts "Area of the box is : #{a}"

结果：

zzl@zzl-VirtualBox:~/rubyprojects$ ruby demo_instancemethod.rb
Area of the box is : 200

1.7 The class Methods and Variables

class variables 类变量，是在类实例中共享。 也就是说一个变量实例，被对象实例访问。类变量以俩个@@开头。必须在类定义时初始化。.

class method类方法用 def self.methodname() 来定义，以end 结束。用 类名.方法名 classname.methodname 来访问。

class Box
   # Initialize our class variables
   @@count = 0
   def initialize(w,h)
      # assign instance avriables
      @width, @height = w, h

      @@count += 1
   end

   def self.printCount()
      puts "Box count is : #@@count"
   end
end

# create two object
box1 = Box.new(10, 20)
box2 = Box.new(30, 100)

# call class method to print box count
Box.printCount()

运行结果：

zzl@zzl-VirtualBox:~/rubyprojects$ ruby demo_classmethodVar.rb
Box count is : 2

1.8 The to_s Method

每一个类应该定义一个to_s 实例方法，返回表明对象的字符串。

class Box
   # constructor method
   def initialize(w,h)
      @width, @height = w, h
   end
   # define to_s method
   def to_s
      "(w:#@width,h:#@height)"  # string formatting of the object.
   end
end

# create an object
box = Box.new(10, 20)

# to_s method will be called in reference of string automatically.
puts "String representation of box is : #{box}"

运行结果：

zzl@zzl-VirtualBox:~/rubyprojects$ ruby demo_tostring.rb
String representation of box is : (w:10,h:20)

1.9 Access Control

Ruby 提供了三种对实例方法的保护 public, private, or protected. Ruby 对类变量和实例的访问没有控制。

Public Methods − 公共方法，均可以访问。除了初始化方法默认是private，其它默认是公共的。
Private Methods − 私有方法不能从类外部访问，查看。只有类方法能够访问私有方法。.
Protected Methods − 保护方法不能被外部调用，只有被定义的类及其子类的对象调用。

# define a class
class Box
   # constructor method
   def initialize(w,h)
      @width, @height = w, h
   end

   # instance method by default it is public
   def getArea
      getWidth() * getHeight
   end

   # define private accessor methods
   def getWidth
      @width
   end
   def getHeight
      @height
   end
   # make them private
   private :getWidth, :getHeight

   # instance method to print area
   def printArea
      @area = getWidth() * getHeight
      puts "Big box area is : #@area"
   end
   # make it protected 修改成保护，则不能被外部调用。
   protected :printArea
   def ex_printArea
       self.printArea()
   end

end

# create an object
box = Box.new(10, 20)

# call instance methods
a = box.getArea()
puts "Area of the box is : #{a}"

box.ex_printArea()

# try to call protected methods
box.printArea()

第一个第二个方法成功，第三个方法出错。保护的不能直接调用，可是在能够在类内被self调用。

zzl@zzl-VirtualBox:~/rubyprojects$ ruby demo_rubyAccessControl.rb
Area of the box is : 200
Big box area is : 200
Traceback (most recent call last):
demo_rubyAccessControl.rb:48:in `<main>': protected method `printArea' called for #<Box:0x0000556a4ab600d0 @width=10, @height=20, @area=200> (NoMethodError)
Did you mean?  printArea
               ex_printArea

1.10 Class Inheritance 类继承

面向对象的最重要概念就是继承。继承能够用其它类定义新的类，便于建立和维护应用。

Inheritance also provides an opportunity to reuse the code functionality and fast implementation time but unfortunately Ruby does not support multiple levels of inheritances but Ruby supports mixins. A mixin is like a specialized implementation of multiple inheritance in which only the interface portion is inherited.

继承能够代码复用，加速开发。不过Ruby 不支持多重继承，可是提供了混合机制mixins. 混合像多重继承的一个特殊实现，只有界面interface被继承。

以存在的类称做基类或超类base class or superclass，新建的类叫派生类或子类 derived class or sub-class.

Ruby支持子类概念，即继承。在子类名字后加<基类名。

下面例子定义BigBox 做为 Box 的子类

# define a class
class Box
   # constructor method
   def initialize(w,h)
      @width, @height = w, h
   end
   # instance method
   def getArea
      @width * @height
   end
end

# define a subclass
class BigBox < Box

   # add a new instance method
   def printArea
      @area = @width * @height
      puts "Big box area is : #@area"
   end
end

# create an object
box = BigBox.new(10, 20)

# print the area
box.printArea()

结果

zzl@zzl-VirtualBox:~/rubyprojects$ ruby demo_inheritbox.rb
Big box area is : 200

1.11 Methods Overriding

你能够在派生类添加新的功能，但有时候想修改父类定义的方法。你能够保持一样的方法名，从新定义方法，这称做c重写overriding .

demo_overriding.rb

# define a class
class Box
   # constructor method
   def initialize(w,h)
      @width, @height = w, h
   end
   # instance method
   def getArea
      @width * @height
   end
end

# define a subclass
class BigBox < Box

   # change existing getArea method as follows
   def getArea
      @area = @width * @height
      puts "Big box area is : #@area"
   end
end

# create an object
box = BigBox.new(10, 20)

# print the area using overriden method.
box.getArea()

1.12 Operator Overloading

将操做符从新定义，叫作操做符重载。如下就是定义盒子+,-,* 操做符重载的例子。

class Box
   def initialize(w,h)     # Initialize the width and height
      @width,@height = w, h
   end

   def +(other)       # Define + to do vector addition
      Box.new(@width + other.width, @height + other.height)
   end

   def -@           # Define unary minus to negate width and height
      Box.new(-@width, -@height)
   end

   def *(scalar)           # To perform scalar multiplication
      Box.new(@width*scalar, @height*scalar)
   end
end

1.13 Freezing Objects 冻结对象

有时候，不想一个对象被改变。对象的冻结方法容许如此作，将对象变成一个常量。任何对象能够调用Object.freeze来冻结。. 被冻结的对象不能改变。

使用Object.frozen? 来检查对象是否被冻结。

demo_freeze.rb

# define a class
class Box
   # constructor method
   def initialize(w,h)
      @width, @height = w, h
   end

   # accessor methods
   def getWidth
      @width
   end
   def getHeight
      @height
   end

   # setter methods
   def setWidth=(value)
      @width = value
   end
   def setHeight=(value)
      @height = value
   end
end

# create an object
box = Box.new(10, 20)

# before object is frozen
# use accessor methods 
x = box.getWidth() 
y = box.getHeight() 
puts "Width of the box is : #{x}" 
puts "Height of the box is : #{y}"

# let us freez this object
box.freeze
if( box.frozen? )
   puts "Box object is frozen object"
else
   puts "Box object is normal object"
end

# now try using setter methods
box.setWidth = 30
box.setHeight = 50

# use accessor methods
x = box.getWidth()
y = box.getHeight()

puts "Width of the box is : #{x}"
puts "Height of the box is : #{y}"

执行结果：

zzl@zzl-VirtualBox:~/rubyprojects$ ruby demo_freeze.rb
Width of the box is : 10
Height of the box is : 20
Box object is frozen object
Traceback (most recent call last):
    1: from demo_freeze.rb:45:in `<main>'
demo_freeze.rb:18:in `setWidth=': can't modify frozen Box (FrozenError)

1.14 Class Constants

类常量。你能够在类内定义常量并赋值，而不用@或@@。常量习惯用大写字母。

在类外访问常量方式 classname::constant a

demo_constant.rb

# define a class
class Box
   BOX_COMPANY = "TATA Inc"
   BOXWEIGHT = 10
   # constructor method
   def initialize(w,h)
      @width, @height = w, h
   end
   # instance method
   def getArea
      @width * @height
   end
end

# create an object
box = Box.new(10, 20)

# call instance methods
a = box.getArea()
puts "Area of the box is : #{a}"
puts Box::BOX_COMPANY
puts "Box weight is: #{Box::BOXWEIGHT}"

执行结果

Area of the box is : 200
TATA Inc
Box weight is: 10

类常量能够继承，也能够像实例方法同样被重写。

1.15 Create Object Using Allocate

建立一个对象不调用它的构造器 initialize ，即new 方法，能够使用 allocate。

demo_allocate.rb

# define a class
class Box
   attr_accessor :width, :height

   # constructor method
   def initialize(w,h)
      @width, @height = w, h
   end

   # instance method
   def getArea
      @width * @height
   end
end

# create an object using new
box1 = Box.new(10, 20)

# create another object using allocate
box2 = Box.allocate

# call instance method using box1
a = box1.getArea()
puts "Area of the box is : #{a}"

# call instance method using box2
a = box2.getArea()
puts "Area of the box is : #{a}"

执行结果

zzl@zzl-VirtualBox:~/rubyprojects$ ruby demo_allocate.rb
Area of the box is : 200
Traceback (most recent call last):
1: from demo_allocate.rb:27:in `<main>'
demo_allocate.rb:12:in `getArea': undefined method `*' for nil:NilClass (NoMethodError)

1.15 Class Information

若是一个类是可执行代码，这暗示它们在some个对象的context 中执行。

下例返回类的类型和名字。

class Box
   # print class information
   puts "Type of self = #{self.type}"
   puts "Name of self = #{self.name}"
end

结果

Type of self = Class
Name of self = Box

Ruby 简明教程 高级进阶 Part 1

Ruby 简明教程

高级进阶

1. Ruby - Object Oriented 面向对象

1.1Ruby Class Definition

1.2 Define Ruby Objects

1.3 The initialize Method

1.4 The instance Variables

1.5 The accessor & setter Methods

1.6 The instance Methods

1.7 The class Methods and Variables

1.8 The to_s Method

1.9 Access Control

1.10 Class Inheritance 类继承

1.11 Methods Overriding

1.12 Operator Overloading

1.13 Freezing Objects 冻结对象

1.14 Class Constants

1.15 Create Object Using Allocate

1.15 Class Information

Ruby 简明教程高级进阶 Part 1