easai on Programming

TreeEditor is a Java GUI component for editing tree structure.  It is a JScrollPane (as of TreeEditor ver. 0.1.0) derived and you can directly embed the component in your app.  I would suggest using JSplitPane . First and foremost, load the TreeEditor-0.1.5 library (if you are using Maven) as follows. < dependency > < groupId > com.github.easai.utils </ groupId > < artifactId > TreeEditor </ artifactId > < version > 0.1.6 </ version > </ dependency > Instantiate TreeEditor with a file name (or an empty string).    Initialize it by calling TreeEditor#init() .  Here I put it in a JSplitPane  and the TreeEditor will be resizable as the pane resizes. TreeEditor treeEditor = new TreeEditor( "" ); JTextArea menuCode = new JTextArea(); JTextArea listenerCode = new JTextArea(); public void init () { treeEditor. init ();...

The term "recursive" means in computer science a function call that calls itself, in a way such that you can traverse a tree.  A tree contains nodes and leaves.  You would process the leaves and call the function again for nodes recursively. Consider traversing a directory structure.   File#list() does not list up all the subdirectories.  It is a matter of writing a function that calls itself, i.e., process the files and call the same function for directories. This procedure can be generalized.  Instead of writing the recursive call, here I wrote a class called RecurseDir .  This is an abstract class that calls on the specified file directory recursively. import java.io.File ; public abstract class RecurseDir { /** * Executed on each file. * * @param fileName */ public abstract void executeOnFile ( String fileName ); /** * Executed on each directory. * * @param fileName */ publi...

Quartz is a Java library that can schdule tasks (using Job derived class).  Let me show how you would use the scheduler.  First, import the library. < dependency > < groupId > org.quartz-scheduler </ groupId > < artifactId > quartz </ artifactId > < version > 2.3.0 </ version > </ dependency > < dependency > < groupId > org.quartz-scheduler </ groupId > < artifactId > quartz-jobs </ artifactId > < version > 2.3.0 </ version > </ dependency > The task that the scheduler runs must be a Job class derivative. import org.quartz.Job ; import org.quartz.JobExecutionContext ; import org.quartz.JobExecutionException ; public class NewsJob implements Job { @Override public void execute ( JobExecutionContext context ) throws JobExecutionException {...

JSON is a "fat-free alternative" of XML format, or the structured dataset format.  Here is a Java code that reads JSON data supplied by a web service.  Replace the URL and perhaps the API key if the site requires it, and the app will parse the JSON response. First of all, edit your POM (pom.xml). < dependency > < groupId > com.github.cliftonlabs </ groupId > < artifactId > json-simple </ artifactId > < version > 2.1.2 </ version > </ dependency > Here is how you can parse the JSON. import java.io.BufferedReader; import java.io.InputStreamReader; import java.net. URL ; import org.json.simple.JSONArray; import org.json.simple.JSONObject; import org.json.simple.parser.JSONParser; @SuppressWarnings( "deprecation" ) public class NewsApp { public static void main( String args[]) { JSONParser parser = new JSONParser(); Strin...

There are ways in Java how you can read or write  XML files.  Here is a way of reading and writing a XML file using DOM. The function readXML() reads the specified file.  It does all the preliminary works for reading an XML file.  It creates DocumentBuilderFactory , DocumentBuilder , and Document .  The XML file will be read by calling DocumentBuilder#parse(). The parseXMLTree() function recursively parses the DOM tree.  It outputs the text contents of each <value> tag of the node.  A word of caution: it is not Node#getNodeValue() that retrieves the text content of the node.  Call Node#getTextContent() instead. The function writeXML() does all the work for writing out the XML.  It creates TransformerFactor , Transformer , and DOMSource .  The StreamResult object creates the stream for the specified file.  Finally, call Transformer#transform() and it will write out the XML. import javax.xml.parsers.DocumentBuilder;...

How do you use command line arguments in Java?  The Java SDK does not come with library that can parse the arguments.  Parsing each argument is a tedious work, however. The common-cli does the all the work for you.  The library can parse the input for short and long versions of the command line input.  The "-f" option should be the same with "--trefile" , that is.  The options can be optional or mandatory.  If the required option is not there, it will print out the usage as specified.  Nice, is it?  It only is a matter of editing the pom.xml .  Here you go:   < dependency > < groupId > commons-cli </ groupId > < artifactId > commons-cli </ artifactId > < version > 1.4 </ version > </ dependency > As for parsing the input arguments, set the Option and parse the command line with CommandLineParser with the option settings.  If any wrong option is set, the usa...

How do you trace your app?  Well, simple standard output is enough for simple applications.   What if, however, you'd want layered commeting/tracing?  Supposing, say, you do not want lengthy trace info for regular use of your app?  The error reports certainly should be distinguished from debugging info. Logback is a nice package that does the work.  Your app will emit any sort of messages, with proper labels (error, warning, info, debug, trace).  Load the library by editing pom.xml file.   < dependency > < groupId > ch.qos.logback </ groupId > < artifactId > logback-classic </ artifactId > < version > 1.2.2 </ version > </ dependency > The log file should be specified in logback.xml file.  The file should be under src/main/resources.   <? xml version = "1.0" encoding = "UTF-8" ?> <! DOCTYPE logback > < config...

In the last blog, I showed you some of the cases that uses the library in the Central Repository with Maven.  In the following test cases, I show you how the library can be incorporated into your project by using Maven ( ComplexMaven ) and Gradle ( ComplexGradle ).  The projects uses the library called Complex .  Complex is available from the Central Repository.  Maven and Gradle use different configuration files for library dependency. In case with Maven, the library dependency is in the pom.xml file (POM file).  The file format goes as folllows:   < dependency > < groupId > com.github.easai.math </ groupId > < artifactId > Complex </ artifactId > < version > 0.0.1 </ version > </ dependency > If you are using Gradle, the configuration should be in the build.gradle file.   compile group: 'com.github.easai.math', name : 'Complex', version ...

Using Maven, the library management is as intuitive as it could ever be.  "DLL hell" headache is over by specifying the version of the library in the project pom.xml file.  Furthermore, all JAR files are managed and stored locally as any requests are made by the project. Maven configuration is specified in a file called POM, specified in pom.xml.  This XML formatted file specify all that the compiler would need, including the package configuration and libraries. If you are not using Maven and copying the Complex library JAR file into your project library, the library management is manual.  Which means, you would have the same copy of the JAR files all over the place for whichever project that needs it.  If the library is updated, you would download the updated file for all the projects that use the library. Supposing you have Complex library and your projects Mandelbrot and Misiurewicz  need that library. Using Maven, incorporating that library is a...