Cognition: December 2011

Wednesday, December 28, 2011

Useful eclipse plugins

Eclipse XPath evaluation plugin
http://marketplace.eclipse.org/node/148833

Sunday, December 25, 2011

Useful eclipse plugins

syntaxhighlighter

syntaxhighlighter for highlighting code in blogger: http://alexgorbatchev.com/SyntaxHighlighter/integration.html

SCJP

package test1;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

interface IMain
{
    // interface method can declare exception in its signature
    void method() throws Exception;

    //void method6();
}

public class Main implements IMain
{
    // main can be final, can be overridden, cmd line arg starts with parameters
    public static void main(String[] str) throws ClassNotFoundException
    {
        System.out.println("Main");
        new Main().method1();
    }

    //constructor can throw exception
    public Main() throws ClassNotFoundException
    {
        throw new ClassNotFoundException();
    }

    public void method()
    {

    }

    public void method1()
    {
        //can have empty try catch block
        try
        {

        }
        // j2se 7 feature
        catch (Exception | Error e)
        {
            //suppresed exception
            e.getSuppressed();
        }
        System.out.println("Hurray1");
        try
        {
            this.method2();
            System.out.println("Hurray3");
        }
        // Need to either handle exception or propogate exception, only finally will not suffice
        catch (ClassNotFoundException e)
        {
            e.printStackTrace();
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        // can catch a error too but not a good practise
        catch (Error e)
        {

        }
        catch (Throwable e)
        {

        }
        // finally should be at the end of all catch
        finally
        {

        }
        //Perfectly valid without catch clause, when try is empty or has method which throws RTE
        //try
        //{
        //}
        //finally
        //{
        //}
        System.out.println("Hurray2");
        // just like runtime exception need not specify
        throw new Error();
    }

    // Make throw different exception which is higher in hierarchy
    void method2() throws Exception
    {
        throw new ClassNotFoundException();
    }

    // method may thow multiple exception
    void method3() throws ClassNotFoundException, InterruptedException
    {
        throw new ClassNotFoundException();
    }

    void method5() throws ClassNotFoundException
    {
        throw new ClassNotFoundException();
    }

    // cannot throw exception if superclass doesn't declare
    //    public void method6() throws FileNotFoundException
    //    {
    //
    //    }
}

class Main1 extends Main
{
    // even static method is overriden, however usually we associate static method with class name
    // and do not show it as overriden
    public static void main(String[] str)
    {
        System.out.println("Main1");
        java.nio.charset.Charset charset = java.nio.charset.StandardCharsets.US_ASCII;
        java.nio.file.Path outputFilePath = null;
        try
        {
            outputFilePath = java.nio.file.Paths.get(new URI("name"));
        }
        catch (URISyntaxException e)
        {
            e.printStackTrace();
        }
        // j2se 7 feature try with resources - AutoClosable interface
        try (java.io.BufferedWriter writer = java.nio.file.Files.newBufferedWriter(outputFilePath, charset, null);)
        {

        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }

    /**
     * Constructs a new Main1.
     */
    public Main1() throws ClassNotFoundException
    {
        super();
    }

    // overriding method cannot throw exption higher in hierarchy that is defined by super class 
    void method2() throws ClassNotFoundException
    {

    }

    // overriding method may chose not to throw exception at all even if super class 
    // method is throwing, can throw differnt exception.
    void method3()
    {
    }

    // Sub class cannot throw exception which is not thrown by superclass or
    // not in hierarchy of class.
    //    void method5() throws FileNotFoundException
    //    {
    //    }
}

References:
http://docs.oracle.com/javase/tutorial/essential/exceptions/index.html
http://www.javabeat.net/tips/133-handle-exceptions-in-overriding-methods.html
http://www.csie.ntut.edu.tw/labsdtl/95-1/1206-1.pdf
http://www.javamex.com/tutorials/exceptions/exceptions_hierarchy.shtml

I started my career programming in c and assembly languages. It was only later after few years I switched over to java programming. I used to use Netbeans initially, but there was something about eclipse that I fell in love with.

Step 1:
Download and install eclipse IDE from link below.
http://www.eclipse.org/downloads/

Step 2:
Tweak the [Eclipse Home]/eclipse.ini if needed:

 
 -startup
 plugins/org.eclipse.equinox.launcher_1.2.0.v20110502.jar
 --launcher.library
 plugins/org.eclipse.equinox.launcher.win32.win32.x86_1.1.100.v20110502
 -showsplash
 org.eclipse.platform
 --launcher.XXMaxPermSize
 --launcher.defaultAction
 openFile
 -vmargs
 -Xms40m
 -Xmx768m

Step 3:

Tweak the Eclipse preferences.

Wednesday, December 28, 2011

Useful eclipse plugins

Sunday, December 25, 2011

Useful eclipse plugins

syntaxhighlighter

SCJP

Eclipse IDE tips