Tim Evans Java Tips Page

• JavaDoc notes
• Java File Separator
• Java Path Separator
• Java and System Environment Variables

I use the free Netbeans IDE for programming. Eclipse is the other good option.

The CERN Colt routines are good for lists (vectors, variable length arrays) linear algebra and data analysis. I have yet to find a readable introduction to this package or simple examples but they must be out there.

The JUNG java graph library looks very good for networks but I have yet to break into it. There are good example routine provided but the manual lags well behind the implementation. I have also found it to be very slow on some occasions. I suspect I do not know how to use it efficiently and that my Java needs to be improved to get the most out of this. The JUNG wiki might provide the answers to my problems.

David Eck's Java Notes are an excellent and free introduction. I even bought the printed version as I liked them so much. I also use the input routines described in his book which are also provided free, such as textreader.java.

Outputting graphics to bitmap files is easy. For instance look at the GraphEditorDemo.java in the JUNG package. Postscript or other vector file output is less trivial. The VectorGraphics library of FreeHEP Java Libraries looks very useful and claims to contain PostScript, PDF, EMF, SVF, and Flash SWF, along with the image formats GIF, PNG, JPG and PPM. I have also seen recommended jlibeps which is a fork of the no longer free (if cheap) EpsGraphics2D.

Options parsing looks easy using the ritopt package but I have yet to try it.

Running java code

java -Xmx2000m  -classpath "%PRGDIR%\JAVA\TheProject\dist\project.jar";. project.MakeNetworks %1 %2 %3 %4 %5 %6 %7 %8 %9

Unfortunately it appears it is easy to have several versions of java of different ages and types (32 or 64 bit) so be careful. It is not always obvious which one plain java calls when entered from the command line. The Program Files holds the java files in a java directory however it is possible that other programmes have their own versions and that these are being run. I found QuickTime on my system was messing things about. Some commands I find useful to work out what is going on, all run in a command window are as follows

"FULLPATH\java" -version
"FULLPATH\java" -XshowSettings:all

C:\>"C:\Program Files\Java\jre7\bin\java" -version
java version "1.7.0_10"
Java(TM) SE Runtime Environment (build 1.7.0_10-b18)
Java HotSpot(TM) 64-Bit Server VM (build 23.6-b04, mixed mode)

Output Formatting

String outString = String.format("%6.3f",doubleValue);

System.out.printf("%9.3e",doubleValue);

For integers don't use i, the flag is d

String outString = String.format("%6d",intValue);

String Processing

• The Character has some simple tests for the nature of a character including

  Character.isLetter(line.charAt(0))
  Character.isDigit(line.charAt(0))
  Character.isWhiteSpace(line.charAt(0))
  

• Split string into pieces using white space as separators. Note the plus sign in the regex means that consecutive white space characters are treated as a single separator.

  String[] word = line.split("\\s+");

• Split string into pieces using white space or period as separators. The period is another special character so it is escaped. The square brackets gives an OR, i.e. any of the individual characters in the square brackets are matched.

  String[] word = line.split("[\\.\\s]+");

• Replace any character with ASCII code between 0 and 32 inclusive (control characters are less than 32 and the space is number 32) with an underscore

  line.replaceAll("[\\x00-\\x20]", "_");

• To remove white space and other characters such as tab try

  line.replaceAll("\\s","")

• However also note you can trim white space off the front and back of a string with the trim() String method

  line.trim()

• How to convert a string to numbers (use try ... catch to catch failures)

  try{
   double d=Double.parseDouble(line.trim());
   int i=Integer.parseInt(line.trim());
  } catch (RuntimeException e){
   System.err.println("Failed to convert a number"};
  }
  No white space seems to be tolerated by these methods hence the use of the trim() method on the strings first.
  

   @see package.Class
   @see package.Class#field
   @see package.Class#Constructor(Type, Type...)
   @see package.Class#Constructor(Type id, Type id)
   @see package.Class#method(Type, Type,...)
   @see package.Class#method(Type id, Type, id)

{@link package.class#member label}

For URL, in the main text of a javadoc you can use the URL and any text you like (e.g. the full URL)

<a href="http://netplexity.org">http://netplexity.org</a>

@see <a href="http://netplexity.org">http://netplexity.org</a>

For constants it is useful to use the value tag

{@value package.class#field}

If you want to have text in the font used for code without the text being interpreted as HTML markup, e.g. for equations, then try

{@code text}

System.getProperty("file.separator");

System.getProperty("path.separator");

System.getenv(env);

 final String fs = java.lang.System.getProperty("file.separator");
 if (!directoryName.endsWith(fs)) directoryName=directoryName+fs;

• System.getProperty("user.dir") returns a String containing the absolute path name of current directory
• System.getProperty("user.home") returns a String containing the absolute path name of user's home directory

• Array copying use System.arraycopy. For instance replace

  for (int i=0; i
   by
          
  System.arraycopy(inputFriction, 0, friction, 0, friction.length);
  .