大切なもの

大切なもの

私は大切なものが４つあります。

それは健康、家族、仕事、友達。

健康はいちばん大事なものですね。

健康だと仕事もたくさん出来るし恋や幸せや喜びを感じることも出来ます。健康がなかったら、これらのことが難しくなります。

次に家族です。思い出す人がいます。大好きな人がいます。遠い場所へ行ったら、帰りたい場所です。そこは家族です。家族は特別な場所でしょう。

生活するには食べ物が必要です。着る服が必要です。住む家が必要です。車が必要です。旅行したいです。だれかの手伝いをしたいです。また、大好きなことをやりたいです。

それには、お金が要ります。これらの理由のために仕事が大切です。

小さい時学校へ勉強しに行きました。友達と一緒に勉強しました。学校の行事を一緒にやりました。スポーツを一緒にしました。会社で働く時、仲間と一緒に仕事をします。ビールを一緒に飲みます。その人たちは大切な私の友達です。

Understanding Spring @Transactional deeply

This post will try to explain the annotation @Transaction in Spring framwork in detail. I will try to answer the following questions:

1. How can Spring interpret @Transactional?
2. What will Spring do with @Transactional?
3. How to use @Transactional correctly?

I. Aspect Oriented Programming (AOP)
Before we dive into inspecting Spring @Transactional annotation I would like to take a look little at AOP. Because Spring uses AspectJ (AspectJ is an aspect-oriented programming (AOP) extension created at PARC for the Java programming language.) to help parsing @Transactional annotation and then opening transaction before the actual code of the annotated method is executed.

Now let's get started with AspectJ

Step 0:
Download and install IDE Spring Tool Suite (STS) 

Step 1:
Open Spring Tool Suite and create an AspectJ project StudyAJ

Step 2:
Create a package and put Java classes, aspect files into it.

Greeting.java

package com.sonand.studyaj;

public class Greeting {
 public void say(String message) {
  System.out.println(message);
 }
 
 public void sayToCustomer(String message) {
  System.out.println(message);
 }
}

This is a simple java class.

GreetingAspect.aj

package com.sonand.studyaj;

public aspect GreetingAspect {
 pointcut callSayGreeting() :
  call(* *.say*(..));
 
 before() : callSayGreeting() {
  System.out.println("Hi!");
 }
 
 after() : callSayGreeting() {
  System.out.println("Thank you!");
 }
}

This is an simple aspect and it includes aspect keyword, not class keyword. I will explain it in detail later.

Main.java

package com.sonand.studyaj;

public class Main {

 public static void main(String[] args) {  
  Greeting gt = new Greeting();
  gt.say("Can I help you?");
  System.out.println("\n---------------------------------------------------");
  gt.sayToCustomer("Are you okay there?");
 }

}

To compile this project, Spring Tool Suite will call to AspectJ compiler for compiling file GreetingAspect.aj automatically. Now let's run it.

Output:

Hi!
Can I help you?
Thank you!

---------------------------------------------------
Hi!
Are you okay there?
Thank you!

From the above output we see that each time main program call a method of Greeting object for outputting a greeting message, other messages are also output right above and right below the greeting message. These additional messages originate from the aspect GreetingAspect. More specifically, these messages originate from advice before() and advice after(). 

Advice
Advice is a terminology in AOP world and it will execute additional code we added. How is advice kicked in? The answer is: an advice is kicked in when the pointcut attached to it is matched. We go to another terminology pointcut.

Pointcut
A pointcut is a program element that picks out join points and exposes data from the execution context of those join points. Pointcuts are used primarily by advice. They can be composed with boolean operators to build up other pointcuts.In aspect GreetingAspect there is a pointcut with name callSayGreeting() and it is defined:

pointcut callSayGreeting() :
  call(* *.say*(..));

where, pointcut is keyword, callSayGreeting() is pointcut name, call(...) is pointcut type. The part with wildcards "* *.say*(..)" is called jointpoint.

Jointpoint
A jointpoint is one or many points in a program's execution. For example, joinpoint could define call/execute to specific methods in a class.

Here, we defined jointpoint "* *.say*(..)". This jointpoint will match any public/protected method from any class. Method name starts with string "say" and has any parameters.

Put it together: when the main program call a method of Greeting object starting with string "say" the pointcut callSayGreeting() will be matched. Because this pointcut is attached to advices before() and after() these advices will be kicked in respectively. Firstly, the advice before() is executed, then the called method is executed and finally the advice after() is executed. That's all.

Apart from the pointcut call(...) AspectJ also offers other pointcut types. Similarly, AspectJ also offer other advices other than before() and after(). In the next part I will reveal other pointcuts and other advices used by Spring. For more information about AspectJ, please read https://eclipse.org/aspectj/docs.php

Support page for Japanese Vocabulary Game

This is support page for iOS application Japanese Vocabulary Game. Currently, this application is ready on App Store. Please download it from the following hyperlink:
https://itunes.apple.com/us/app/japanese-vocabulary-game/id1050638848

The below is information about developer and application description.

Application: Japanese Vocabulary Game
Devices: Universal iOS Devices
Developer: Son Nguyen

Description:
As you know, when you learn a new language which is not your mother tongue, the most important thing is vocabulary. Vocabulary plays a role of bricks to build up meaningful sentences. From this reason, Japanese Vocabulary Game is developed to help you memorize new Japanese words in a pleasing manner. If you are learning Japanese or English, then this application is for you. Let's enjoy it!

Usage:

1. Home screen

- Button Play Now:
    For entering Game screen

- Button View Rank:
    For viewing player's rank in Leaderboard

- Button Update Vocabulary:
    If you touch on this button, the application will download a metadata file from GitHub. Then, it checks the number of vocabularies described in the metadata to know whether or not the vocabulary list was updated. If the vocabulary list was updated, the application will download the corresponding vocabulary list.

The below screenshot shows confirmation dialog when button Update Vocabulary is touched.

2. Game screen
If button Play Now is touched, then you will enter Game screen. Here, you must choose the correct answer in English for the displayed Japanese vocabulary.

3. Game Over screen
If you are in Game screen and you choose a wrong answer, then the Game Over screen will be showed as the following screenshot:

4. Leaderboard screen
If button View Rank is touched (from Home screen or from Game Over screen), then the Leaderboard screen is displayed. To view your rank, please touch on the Leaderboard with name Japanese Vocabulary.

If you have any question or suggestion or problem, please send me an email or drop here a comment.
Thank you very much!
Son Nguyen