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#== Never use for, unless you know exactly why. Most of the time iterators should be used instead. for is implemented in terms of each (so you're adding a level of indirection), but with a twist - for doesn't introduce a new scope (unlike each) and variables defined in its block will be visible outside it.
arr = [1, 2, 3]

# bad
for elem in arr do
  puts elem
end

# good
arr.each { |elem| puts elem }

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 // Condition and ReentrantLock
 class BoundedBuffer {
   final Lock lock = new ReentrantLock();
   final Condition notFull  = lock.newCondition(); 
   final Condition notEmpty = lock.newCondition(); 

   final Object[] items = new Object[100];
   int putptr, takeptr, count;

   public void put(Object x) throws InterruptedException {

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    @unsold = SellInfo.where("user_id = ? and deal_status != 'sold'", current_user.id)
    @sold = SellInfo.where("user_id = ? and deal_status = 'sold'") 

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class SellInfo < ActiveRecord::Base       
  belongs_to :book      
  belongs_to :user

  scope :onsale,:conditions => ['deal_status is not "sold"']                  
  scope :saled,:conditions => {:deal_status => "sold"}                        
end

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#TODO

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(req.save == nil)? false:true

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flash[:notice] = "Item successfully saved as your favourite!"

#很奇怪，看官方文档，rails3里应该flash消息应该可以直接用notice(类似： redirect_to :action=>:XXX,:notice => "msg"),但我试了不行，不知为何，所以这儿还是用的老的style,记下备忘。

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rails generate migration add_password_to_users encrypted_password:string

class AddPasswordToUsers < ActiveRecord::Migration
  def self.up
    add_column :users, :encrypted_password, :string
  end

  def self.down
    remove_column :users, :encrypted_password
  end

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class AddIndexToFavourites < ActiveRecord::Migration
  def self.up
    add_index :favourites,[:user_id,:sell_info_id],:unique => true
  end

  def self.down
    remove_index :favourites,[:user_id,:sell_info_id]
  end
end