Blog of Meng Yan

Morgan wrote a good article which discussed how debugger works. You can check
this entry here(This article is in Chinese ).

I noticed one code in Morgan’s comments:

So, do you know why he use “do {} while (0)” instead of “{}” ?　

Here’s the explanation:

do..while(0) in macro of LINUX kernel

More entries about : Code

Do you know how to use lazy initialization in Java? There’s already many thread discussing this problem in the comunity, just to conclude here.

Due to the JVM memory model, Double-Checking Locking (DCL) will not work in Java, I’d like to recommend two articles talking about this.

The "Double-Checked Locking is Broken" Declaration

Double-checked locking and the Singleton pattern

There’s another article tell you exactly what synchronized really means, very helpful

Double-checked locking: Clever, but broken

One possible way to use lazy initialization in Java:

In the end, attach two articles about Singleton in C# in MSDN, there’s no problem using DCL in C#.

Implementing Singleton in C#

Exploring the Singleton Design Pattern

More entries about : none

Just read Ray Ozzie’s post of “Really Simple Sharing” and many comments, mark it here.

“Microsoft XML News” - Tim Bray

“Sharing at so many levels!” - Dave Winer

“Microsoft proposal: Simple Sharing Extensions for RSS and OPML” - Alex Barnett

“RSS + OPML/ SSE = Really Simple Synchronization”

And here’s the SSE spec

Simple Sharing Extensions for RSS and OPML 

More entries about : XML, RSS, SSE, OPML

I ever write an article about the event handling of Java and C#, just want to add some of C#’s delegate.

Delegate has no semantics carried, so does interface, it only provide method signatures.

Let’s look at the following example:

Class Person’s execute method will not accept the instance that implements the Gym’s Runnable interface.

But in this case,

It’s no problem for Person’s execute method to accept the Gym’s Runnable delegate.

So, delegate defines a single method signature to be wrapped by a delegate instance, but interface defines a set of method signatures to be implemented by a class.

More entries about : Java, C#, Delegate, Interface

More entries about : Farewell, Sun

JAVA SE 5.0 provides two very useful APIs to help us debug our program, All this two are all class "Thread"’s method:

public StackTraceElement[] getStackTrace()

Returns an array of stack trace elements representing the stack dump of this thread. This method will return a zero-length array if this thread has not started or has terminated. If the returned array is of non-zero length then the first element of the array represents the top of the stack, which is the most recent method invocation in the sequence. The last element of the array represents the bottom of the stack, which is the least recent method invocation in the sequence.

public static Map<Thread, StackTraceElement[]> getAllStackTraces()

Returns a map of stack traces for all live threads. The map keys are threads and each map value is an array of StackTraceElement that represents the stack dump of the corresponding Thread.

We can use this two APIs to get the thread’s stack trace information and help us debug or log. I will give a example that use this to write log.

If we are going to add log before, we need to add a "java.util.logging.Logger" to our class and use it to log. It’s ok and works pretty well, the following code just wanna to give you an example of the new exposed API "getStackTrace".

Caught the meaning? Yes, it’s pretty simple.

sts[0] = java.lang.Thread :: dumpThreads

sts[1] = java.lang.Thread :: getStackTrace

sts[2] = LogTest :: log ( This function )

sts[3] = Where you called the log function

And you can use this stack trace information to finish other features.

More entries about : Stack Trace, Tiger, Java

I have not updated my english blog for a long time, I decided to start a new one here. I will backup all my english posts here, sorry for the incovenience and hope these will do you some help.

BTW: I also write chinese blog, if you are interested, you can access here.

More entries about : English, Blog

One of my US friends ask me how to offset the timestamp of Lilina RSS aggregator. He lives in the east coast but his web host is in the west.

In fact, it’s very easy to do that, and I do think Lilina should add such support.

1) Add the following line in "conf.php"

The value is the timezone offset between your host and your home. (In my case, it’s 12 hours)

2) In "index.php"

Find the following lines:

Add this line:

3) In "lib.php"

Find the function "create_time", then change the line

to

Upload all these three files to your server and test it, it should work well now.

More entries about : Lilina, RSS Aggregator, Timezone, Personal Portal

JSR223 "describe mechanisms allowing scripting language programs to access information developed in the Java Platform and allowing scripting language pages to be used in Java Server-side Applications."

This defines a framework to allow scripting language programs to access information developed in the Java platform. We currently plan to integrate this into Mustang for b40. Aside from the framework, we will also include a JavaScript engine based on the Mozilla Rhino implementation. Later, we hope to include a scripting shell that is script language independent. This will be a very cool way to create a prototype, do some exploratory coding, and learn new APIs.

The latest release of Mustang has already included this feature. You can check out the latest release of JavaSE to have a try.

Read the rest of this entry »

More entries about : Java, Mustang, JSR

Actually, this article is posted about one year before, at here. Today, I happened to see this article, interesting. So, I found my old entry and post here. Also, I post all the comments at the end, it’s really valuable I think.

Recently(2004.08.06), a friend of mine discussed the Event handle issues in C# and Java with me, sounds interesting. I would like to blog the discussion and my investigation here.

C# (pronounced C Sharp) is a programming language developed by MS as part of its .NET platform. When I saw it the first time, I ask myseft:"is it another version of Java?". Just a joke, C# is extremely similar to Java: GC, VM, single inheritance, interfaces, packages(use "using" instead of "import" ), pure OO etc. However, C# also invent many new features, delegate is a famous one.

Ok, let’s talk about the event-handle issues. In Java, we use the well-known Observer Pattern (Gamma et, Design Patterns) to implmented the events. For example, if we wanna to handle the Button’s Click event, we simply add a ActionListener to this button:

Or we can even add listener in following way:

In C#, Anders Hejlsberg introduced the new keyword "delegate", I think it’s actually like the type-safe function pointers. Anders really love the function pointers, he bring this to Delphi & Visual J++ too. Let’s first take a look at how this keyword works:

In Java, Since the listener rely on the interfaces, so, we can not call the methods without knowledge of the target object. For example:

A more complex example is the method whose name can be variant, you can find detail information in this article.

Although these two classes have common method, but because they do not share a common interface, so, we can not call them in a uniform way. How to solve the problem? In Java, we can use the Proxy Pattern(Gamma et, Design Patterns) and Adapter Pattern(Gamma et, Design Patterns) or use the reflection mechanism to solve the problem. In C#, ok, it’s delegate’s work.

The most important usage of delegates is for event handling:

Ok, that is the mechanism C# handle events. How about it? I think everyone has his cents. In my opnion, at the first look, it’s very attractive to me, things get easy now. But soon I feel uncomfortable. I don’t think this function pointer-like mechanism should exist in a pure OO languages . So, I would rather to use patterns to keep the code clean.

To summarize:
At the above situation:
1) If I can controll all the code, then I would rather retrofit a common interface that has "show" method;
2) If things are not that easy, for example: all classes are library codes, or method has different name, I’d like to use adapter and proxy pattern to solve this problems.

Just my cents.

Woty - not bad. delegate is some how usefule. but i think method should not be the first-class object. In common OO theory: Class := data + operation on data. if member operation is first-class, how about member varible?

Mijia - I think the delegate is just the wrapper for the function pointer or callback function in C/C++, which cannot be appeared in Java or C#, because they have their restrict security architecture. As well as first class object discussed, I do not know the exact ly defined concept, so I could not tell which idea would be correct. But I would like to regard it like that callback function or function pointer seems very dangerous in C/C++, but it is a fantastic mechanism which could provide flexibility for the software design. And I think Anders Hejlsberg from the C# loved it the most, so he cannot resist to add such mechanism into C#. But in Java, for the consideration of security, the function pointer is strictly forbidden, but Java could use the Reflect to emulate the behavior of the callback function or function pointers. And it is simple and flexible as well. So I think perhaps "function as first class" may be not pretty in the view of grammar or sementics, and in C# it is just one’s idea, some camouflage beneath the security flag.

More entries about : DesignPattern, Java, C#, Delegate, Object-Oriented