An idea is proposed by a PHD student of University of Auckland to check your OO Design on Java. The key point is to use directed graph to analyze the dependencies between all java classes, and the more classses involved in some cycle, the worse design it is.

Several Java Open source softwares have been examed in his research report...
Though it is not the only metric to check your OO design, I'd like to say that it is an interesting thought.
Unlike collection types such as Vector or List, Map (HashTable or HashMap) accesses a value by a key. If we want to retrieve all the values that have been put in a Map, one of simple ways to do that is employing a Collection or plus an Iterator, here is the sample code (just retrieve vaules, skip keys), assuming there is a variable: HashMap<String, <ComplexDataType>> links

Collection c = links.value();
Vector<ComplexDataType> v = new Vector<ComplexDataType>(c);
for(int i = 0; i< v.size(); i++)
{
??? ComplexDataType tempData = (ComplexDataType)v.get(i);
??? dosomethingwith(tempData);
}


P.S. Map provides three views of map: keySet, entrySet and values collection, we can use any of them .
These questions are very useful for some Java newbies and guys who wanna prepare some interviews on Java programming positions, which is really cool.

reference:
http://www.allapplabs.com/interview_questions/java_interview_questions.htm
http://www.allapplabs.com/interview_questions/java_interview_questions_2.htm
http://www.allapplabs.com/interview_questions/java_interview_questions_3.htm
http://www.allapplabs.com/interview_questions/java_interview_questions_4.htm
http://www.allapplabs.com/interview_questions/java_interview_questions_5.htm
http://www.allapplabs.com/interview_questions/java_interview_questions_6.htm
1. Reading text from Standard Input

try 
{
       BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
       String str = "";
       while (str != null) 
       {
          System.out.print("> some prompt ");
          str = in.readLine();
	  dosomethingwith(str);
       }
} 
catch (IOException e) 
{
}

2. Reading text from a file

try 
{
     BufferedReader in = new BufferedReader(new FileReader("filename"));
     String str;
     while ((str = in.readLine()) != null) 
     {
	dosomethingwith(str);
     }
     in.close();
} 
catch (IOException e) 
{
}

3. Reading a file into a BityArray

    // Returns the contents of the file in a byte array.
    public static byte[] getBytesFromFile(File file) throws IOException 
    {
        InputStream is = new FileInputStream(file);

        // Get the size of the file
        long length = file.length();

        // You cannot create an array using a long type.
        // It needs to be an int type.
        // Before converting to an int type, check
        // to ensure that file is not larger than Integer.MAX_VALUE.
        if (length > Integer.MAX_VALUE) 
	{
            // File is too large
        }

        // Create the byte array to hold the data
        byte[] bytes = new byte[(int)length];

        // Read in the bytes
        int offset = 0;
        int numRead = 0;
        while (offset < bytes.length
               && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) 
	{
            offset += numRead;
        }

        // Ensure all the bytes have been read in
        if (offset < bytes.length) 
	{
            throw new IOException("Could not completely read file "+file.getName());
        }

        // Close the input stream and return bytes
        is.close();
        return bytes;

    }

4. Writing to a file

try 
{
    BufferedWriter out = new BufferedWriter(new FileWriter("filename"));
    out.write("some string");
    out.close();
} 
catch (IOException e) 
{
}

Note: If the file does not already exist, it is automatically created.

5. Appending to a file

try 
{
     BufferedWriter out = new BufferedWriter(new FileWriter("filename", true));
     out.write("appending String");
     out.close();
} 
catch (IOException e) 
{
}

6. Using a Random Access File

try 
{
     File f = new File("filename");
     RandomAccessFile raf = new RandomAccessFile(f, "rw");

     // Read a character
     char ch = raf.readChar();

     // Seek to end of file
     raf.seek(f.length());

     // Append to the end
     raf.writeChars("aString");
     raf.close();
} 
catch (IOException e) 
{
}

reference:
http://javaalmanac.com/egs/java.io/pkg.html
volatile

The volatile keyword is used on variables that may be modified simultaneously by other threads. This warns the compiler to fetch them fresh each time, rather than caching them in registers. This also inhibits certain optimisations that assume no other thread will change the values unexpectedly. Since other threads cannot see local variables, there is never any need to mark local variables volatile.

quote from:

http://mindprod.com/jgloss/volatile.html
Though still under voting, it is originally?mentioned by Doug Cutting, and got only positive votes. So it is very likely we can get a 2.0 release version on this Friday. Some bugs has been fixed and deprecated code has been removed in this approaching version. Oops! My laptop, Compaq Presario R3230, is not working now (just worked yesterday evening), blue screen, hangs at disk checking...when I reboot with safe mode, it still hangs at is multi(0)disk(0)rdisk(0)partition(1)\windows\system32\drivers\atisgkaf.sys, I guess there is something wrong with my video driver, but how can I fix that problem without wipe out my documents in harddriver?

I am trying to google by it, it seems some guys also got that problem, some steps are suggested:

1. ?Insert the QuickRestore CD into the CD drive and restart the
? ? system.
2. ?When the red Compaq logo appears, press and hold the Caps
? ? Lock key. ?Next screen will be a blinking QuickRestore screen.
3. ?When the QuickRestore text stops blinking, press and hold the
? ? Num Lock key.

but where can I get QuickRestore CD? included CD seems not in my room any more...anybody has thought about that? + Webcrawler
???
??? -- study open source code
??? ?? ?? purpose: analyze code structure and basic componences
??? ?? ?? focus on: Nutch (http://lucene.apache.org/nutch/)
??? ??? ??? ??? ??? & HTMLParser (http://htmlparser.sourceforge.net/)
??? ?? ?? ?? ?? ?? ? & GData(http://code.google.com/apis/gdata/overview.html)

??? -- understand PageRank idea
??? ?? relative articles:
??? ?? http://en.wikipedia.org/wiki/PageRank
??? ?? http://www.thesitewizard.com/archive/google.shtml
?????? paper : "PageRank Uncoverd" by Chris Ridings and Mike Shishigin
?????? http://www.rankforsales.com/n-aa/095-seo-may-31-03.html (about Chris Ridings & SEO)
??? ?? http://en.wikipedia.org/wiki/Web_crawler (basic idea about crawler)
??? ??
??? -- familar with RSS & Atom protocol

??? -- sample coding:
??? ?? Interface: Scheduler for fetching web links
??? ?? Interface: Web page paser/Analyzer --> to deal with XML-based websites(Weblogs or news sites, RSS & Atom) --> Paser classes based on SAX parser
??? ?? Interface: Retractor/Fetcher --> to get links from page
??? ?? Interface: Collector --> check URL whether duplicated and save in URL database with certian data structure
??? ?? Interface: InformationProcesser --> PageRank should be one important factor --> (under thinking)
??? ?? Interface: Policies(Filter) --> will be served for Collector and InformationProcessor --> (under thinking)

+ Indexer/Searcher (almost done base on Lucene)
Motivation:

always, if you wanna check/analyze source code or do some contribution in open source communities, you would like to download the source code of some projects and load (or import) it into your own IDE. (if you don't wanna use CVS or SVN)

Following is my favorite way to do that under Eclipse:

1. create a new blank Java project:

File -> New -> Project ... -> Java Project --> Next >> -> input the project name (project layout: Create seperate source and output folders) --> click Finish

2. right click Source Folder "src" --> import ... -> select File system -> choose correct source code folder where you put the downloaded source code by click the top "Browse..." button (source code folder means the root folder? thus can keep folder structure as package structure) --> Finish

3. if you import wrong source code folder, you can delete whole project to redo. (it is no use merely deleting some failed packages)

Note:

if there is Ant build file (some stuff like build.xml) included in source code package, that will be cool, just using File -> New -> Project... -> Java Project from Existing Ant Buildfile.

The behavior of a web crawler is the outcome of a combination of policies:

• A selection policy that states which pages to download.
• A re-visit policy that states when to check for changes to the pages.
• A politeness policy that states how to avoid overloading websites.
• A parallelization policy that states how to coordinate distributed web crawlers.

cite from:

http://en.wikipedia.org/wiki/Web_crawler
Problem Description:

I wanna build GData source code under Eclipse which contrains creating type-specific map codes, the Eclipse IDE will complain something like that:? Syntax error, parameterized types are only available if source level is 5.0

Reason:

The new feature to create a type-specific map can only be supported at source level 5.0

Solution:

Do some IDE compiler configuration:
Window > Preferences > Java > Compiler > Compiler compliance level => 5.0

Note:
1. type-specific map:? create a map that will hold only objects of a certain type
??? example:

Map<Integer, String> map = new HashMap<Integer, String>();

    map.put(1, "first");
    map.put(2, "second");

2. if source level 5.0 is applied, Type-safe problem should be noticed for collection data type, such as Vector, List, Stack or Map etc.
that means, you can write code under level 1.4 like this:

private Vector MyList = new Vector();
...
MyList.add(str);

you'd better change to some stuff like this under level 5.0:

private Vector<String> MyList = new Vector<String>();



1. Develop a searching engine merely for Weblogs (Main jobs will be on WebCrawler, Indexer and Searcher part has been done for xml-based information retrieval)

Motivation:
?? ?a. Weblog is more and more popular recently
?? ?b. Though there has some weblog search engines such as Technorati and Blogdigger, but still seems lots of work need to do.
?? ?c. the formats of weblog feed (RSS2.0 & Atom) are xml-based and more standard, which is very close to my current job on xml-based information retrieval
?? ?d. easily extensible for crawling xml-based information websites besides weblogs
?? ?
HOWTO:
?? ????? a. Utilize GData for feeding xml-based information
or????? b. using some Open Source Crawlers + Lucene (similar idea in this article)
or ?? ? c. develop and merge my own simple Crawler package into my Shemy project which is clustering structure searching engine design based on Lucene

???????? likely: c > a > b (coz most open source crawlers are supposed to deal with much complex web pages/links, while since weblog feed is simpler, the crawler for it should be lighter)

Requirement/Functionality Analysis : (in progress)

Schedule: (in progress)

2. Exploration of performation tuning on searching issues to improve Shemy kernel Definition:

A class within another class

Example:

class EnclosingClass 
{
    ...
    class ANestedClass 
    {
        ...
    }
}

Purpose:

Reflect and enforce the relationship between two classes. (esp. in the scenarios that the nested class makes sense only in the context of its enclosing class or when it relies on the enclosing class for its functionthe nested class makes sense only in the context of its enclosing class or when it relies on the enclosing class for its function)

Interesting features:

1. An instance of InnerClass can exist only within an instance of EnclosingClass
2. InnerClass instance has direct access to the instance variables and methods of its enclosing instance.
3. two special kinds of inner classes: local classes and anonymous classes

reference:
http://java.sun.com/docs/books/tutorial/java/javaOO/nested.html