LOYOLITE: November 2011

Sunday, November 27, 2011

Interface

In general, interface is the way just to say something to a media by using another media. Let's take the general life example. TV Remote is the interface because it is the medium to give the command to a TV in order to change the channels or to ON/OFF the TV. Electric switch is also the interface's example.

But in java programming language interface is nothing but the collection of methods with empty implementations and constants variables (variables with static and final declarations). All the methods in an interface are "public and abstract" by default. Since interfaces are abstract in nature so they can not be directly instantiated. To define the methods of an interface the keyword "implements" is used.

Interfaces are similar to abstract classes but the major difference between these two is that interface have all the methods abstract while in case of abstract classes must have at least one abstract method. Interface combines the two functionality (template and multiple inheritance) of C++ language into one (in itself).

Interface Definition

visibility mode interface InterfaceName {
constant variable declarations
abstract method declarations
}

e.g.

public interface RacingCar {
  public void startcar (int Obj);
  public void changegear (int Obj);
  public void incrrace (int Obj);
  public void stopcar (int Obj);
}

Marker Interface
In java language programming, interfaces with no methods are known as marker interfaces. Marker interfaces are Serializable, Clonable, SingleThreadModel, Event listener. Marker Interfaces are implemented by the classes or their super classes in order to add some functionality.
e.g. Suppose you want to persist (save) the state of an object then you have to implement the Serializable interface otherwise the compiler will throw an error. To make more clearly understand the concept of marker interface you should go through one more example.
Suppose the interface Clonable is neither implemented by a class named Myclass nor it's any super class, then a call to the method clone() on Myclass's object will give an error. This means, to add this functionality one should implement the Clonable interface. While the Clonable is an empty interface but it provides an important functionality.

Difference between Interfaces and abstract classes
Some important difference between Interface and abstract classes are given here

Features	Interface	Abstract Class
Methods	An interface contains all the methods with empty implementation.	An abstract class must have at least one method with empty implementation.
Variables	The variables in interfaces are final and static.	Abstract classes may contain both instance as well as static variables.
Multiple Inheritance	In java multiple inheritance is achieved by using the interface (by implementing more than one interface at a time)	Abstract classes does not provide this functionality.
Additional Functions	If we add a method to an interface then we will have to implement this interface by any class..	In Abstract classes we can add a method with default implementation and then we can use it by extending the abstract class.
Used When	All the features are implemented differently in different objects.	When there are some common features shared by all the objects.
Diff	Can’t have Constructor	Can have Constructor

IMP TIP:

Why u can’t create object for Abstract Class: Since abstract class contains incomplete methods, it is not possible to estimate the total memory required to create an object. So JVM can’t create objects to an abstract class.

Karatsuba algorithm

Key of the Process

The basic step of Karatsuba's algorithm is a formula that allows us to compute the product of two large numbers x and y using three multiplications of smaller numbers, each with about half as many digits as x or y, plus some additions and digit shifts.

Let x and y be represented as n-digit strings in some base B. For any positive integer m less than n, one can split the two given numbers as follows

x = x₁B^m + x₀

y = y₁B^m + y₀

where x₀ and y₀ are less than B^m. The product is then

xy = (x₁B^m + x₀)(y₁B^m + y₀)

= z₂ B^2m + z₁ B^m + z₀

where

z₂ = x₁y₁

z₁ = x₁y₀ + x₀y₁

z₀ = x₀y₀.

Example

To compute the product of 1234 and 5678, choose B = 10 and m = 2. Then

12 34 = 12 × 10² + 34

56 78 = 56 × 10² + 78

z₂ = 12 × 56 = 672

z₀ = 34 × 78 = 2652

z₁ = (12 + 34)(56 + 78) - z₂ - z₀ = 46 × 134 - 672 - 2652 = 2840

result = z₂ × 10^2×2 + z₁ × 10² + z₀ = 672 × 10000 + 2840 × 100 + 2652 = 7006652.

Sunday, November 20, 2011

Enabling JMX on Hibernate.

Here are some instructions for making the Hibernate Statistics JMX MBean available from JBoss.
The example below has been tested with JDK 1.6 and JBoss 4.x.

Then, if you are using Spring, add this to your applicationContext.xml file:

    <bean id="jmxExporter"
        class="org.springframework.jmx.export.MBeanExporter">
        <property name="beans">
            <map>
                <entry key="Hibernate:name=statistics">
                    <ref local="statisticsBean" />
                </entry>
            </map>
        </property>
    </bean> 

    <bean id="statisticsBean" class="org.hibernate.jmx.StatisticsService">
        <property name="statisticsEnabled">
            <value>true</value>
        </property>
        <property name="sessionFactory"><ref local="sessionFactory"/></property>
    </bean>

and then set the hibernate.generate_statistics property in your applicationContext-hibernate.xml file:

 <prop key="hibernate.generate_statistics">true</prop>

When you browse the MBeans (using JConsole.exe - which lives in the bin dir of your JDK 1.5 distribution), you should see Hibernate, if you double click on that node, you should see the Statistics Bean.

Below are a couple of screenshots.

If you are not using Spring, inside StartupListener.java (inside contextInitialized method) add:

import org.hibernate.jmx.*; import javax.management.*; import java.lang.management.ManagementFactory; try { SessionFactory sessionFactory = (SessionFactory)applicationContext.getBean("sessionFactory"); MBeanServer mbeanServer = ManagementFactory.getPlatformMBeanServer(); ObjectName on = new ObjectName("Hibernate:type=statistics,application=appfuse"); StatisticsService mBean = new StatisticsService(); mBean.setStatisticsEnabled(true); mBean.setSessionFactory(sessionFactory); mbeanServer.registerMBean(mBean, on); } catch (Exception e) { log.error("Error registering Hibernate StatisticsService [" + e.getMessage() + "]", e); }

After starting up JBoss, you should be able to attach to the server using JConsole (port 9002, as in the config above). From there, you should see the Hibernate MBean where you can view the statistics that have been collected.

Monday, November 14, 2011

Advanced Commands in Vi

Click here for the Basic VI Commands

General Notes:

1. Before doing anything to a document, type the following command followed by a carriage return: :set showmode

2. VI is CaSe SEnsItiVe!!! So make sure Caps Lock is OFF.

Starting and Ending VI

Starting VI
vi filename	Edits filename
vi -r filename	Edits last save version of filename after a crash
vi + n filename	Edits filename and places curser at line n
vi + filename	Edits filename and places curser on last line
vi +/string filename	Edits filename and places curser on first occurance of string
vi filename file2 ...	Edits filename, then edits file2 ... After the save, use :n

Ending VI
ZZ or :wq or :x	Saves and exits VI
:w	Saves current file but doesn't exit
:w!	Saves current file overriding normal checks but doesn't exit
:w file	Saves current as file but doesn't exit
:w! file	Saves to file overriding normal checks but doesn't exit
:n,mw file	Saves lines n through m to file
:n,mw >>file	Saves lines n through m to the end of file
:q	Quits VI and may prompt if you need to save
:q!	Quits VI and without saving
:e!	Edits file discarding any unsaved changes (starts over)
:we!	Saves and continues to edit current file

Status

:.=	Shows current line number
:=	Shows number of lines in file
Control-G	Shows filename, current line number, total lines in file, and % of file location
l	Displays tab (^l) backslash (\) backspace (^H) newline ($) bell (^G) formfeed (^L^) of current line

Modes

Vi has two modes insertion mode and command mode. The editor begins in command mode, where the cursor movement and text deletion and pasting occur. Insertion mode begins upon entering an insertion or change command. [ESC] returns the editor to command mode (where you can quit, for example by typing :q!). Most commands execute as soon as you type them except for "colon" commands which execute when you press the ruturn key.

Inserting Text

i	Insert before cursor
I	Insert before line
a	Append after cursor
A	Append after line
o	Open a new line after current line
O	Open a new line before current line
r	Replace one character
R	Replace many characters
CTRL-v char	While inserting, ignores special meaning of char (e.g., for inserting characters like ESC and CTRL) until ESC is used
:r file	Reads file and inserts it after current line
:nr file	Reads file and inserts it after line n
CTRL-i or TAB	While inserting, inserts one shift width

Things to do while in Insert Mode:
CTRL-h or Backspace	While inserting, deletes previous character
CTRL-w	While inserting, deletes previous word
CTRL-x	While inserting, deletes to start of inserted text
CTRL-v	Take the next character literally. (i.e. To insert a Control-H, type Control-v Control-h)

Motion

h	Move left
j	Move down
k	Move up
l	Move right
Arrow Keys	These do work, but they may be too slow on big files. Also may have unpredictable results when arrow keys are not mapped correctly in client.
w	Move to next word
W	Move to next blank delimited word
b	Move to the beginning of the word
B	Move to the beginning of blank delimted word
^	Moves to the first non-blank character in the current line
+ or	Moves to the first character in the next line
-	Moves to the first non-blank character in the previous line
e	Move to the end of the word
E	Move to the end of Blank delimited word
(	Move a sentence back
)	Move a sentence forward
{	Move a paragraph back
}	Move a paragraph forward
[[	Move a section back
]]	Move a section forward
0 or \|	Move to the begining of the line
n\|	Moves to the column n in the current line
$	Move to the end of the line
1G	Move to the first line of the file
G	Move to the last line of the file
nG	Move to nth line of the file
:n	Move to nth line of the file
fc	Move forward to c
Fc	Move back to c
H	Move to top of screen
nH	Moves to nth line from the top of the screen
M	Move to middle of screen
L	Move to botton of screen
nL	Moves to nth line from the bottom of the screen
Control-d	Move forward ½ screen
Control-f	Move forward one full screen
Control-u	Move backward ½ screen
Control-b	Move backward one full screen
CTRL-e	Moves screen up one line
CTRL-y	Moves screen down one line
CTRL-u	Moves screen up ½ page
CTRL-d	Moves screen down ½ page
CTRL-b	Moves screen up one page
CTRL-f	Moves screen down one page
CTRL-I	Redraws screen
z	z-carriage return makes the current line the top line on the page
nz	Makes the line n the top line on the page
z.	Makes the current line the middle line on the page
nz.	Makes the line n the middle line on the page
z-	Makes the current line the bottom line on the page
nz-	Makes the line n the bottom line on the page
%	Move to associated ( ), { }, [ ]

Deleting Text

Almost all deletion commands are performed by typing d followed by a motion. For example, dw deletes a word. A few other deletes are:

x	Delete character to the right of cursor
nx	Deletes n characters starting with current; omitting n deletes current character only
X	Delete character to the left of cursor
nX	Deletes previous n characters; omitting n deletes previous character only
D	Delete to the end of the line
d$	Deletes from the cursor to the end of the line
dd or :d	Delete current line
ndw	Deletes the next n words starting with current
ndb	Deletes the previous n words starting with current
ndd	Deletes n lines beginning with the current line
:n,md	Deletes lines n through m
dMotion_cmd	Deletes everything included in the Motion Command (e.g., dG would delete from current position to the end of the file, and d4 would delete to the end of the fourth sentence).
"np	Retrieves the last nth delete (last 9 deletes are kept in a buffer)
"1pu.u.	Scrolls through the delete buffer until the desired delete is retrieved (repeat u.)

Yanking Text

Like deletion, almost all yank commands are performed by typing y followed by a motion. For example, y$ yanks to the end of the line. Two other yank commands are:

yy	Yank the current line
:y	Yank the current line
nyy or nY	Places n lines in the buffer-copies
yMotion_cmd	Copies everything from the curser to the Motion Command (e.g., yG would copy from current position to the end of the file, and y4 would copy to the end of the fourth sentence)
"(a-z)nyy or "(a-z)ndd	Copies or cuts (deletes) n lines into a named buffer a through z; omitting n works on current line

Changing text

The change command is a deletion command that leaves the editor in insert mode. It is performed by typing c followed by a motion. For example cw changes a word. A few other change commands are:

C	Change to the end of the line
cc or S	Change the whole line until ESC is pressed
xp	Switches character at cursor with following character
stext	Substitutes text for the current character until ESC is used
cwtext	Changes current word to text until ESC is used
Ctext	Changes rest of the current line to text until ESC is used
cMotion_cmd	Changes to text from current position to Motion Command until ESC is used
<< or >>	Shifts the line left or right (respectively) by one shift width (a tab)
n<< or n>>	Shifts n lines left or right (respectively) by one shift width (a tab)
<Motion_cmd or >Motion_cmd	Use with Motion Command to shift multiple lines left or right

Putting text

p	Put after the position or after the line
P	Put before the poition or before the line
"(a-z)p or "(a-z)P	Pastes text from a named buffer a through z after or before the current line

Buffers

Named buffers may be specified before any deletion, change, yank or put command. The general prefix has the form "c where c is any lowercase character. for example, "adw deletes a word into buffer a. It may thereafter be put back into text with an appropriate "ap.

Markers

Named markers may be set on any line in a file. Any lower case letter may be a marker name. Markers may also be used as limits for ranges.

mc	Set marker c on this line
`c	Go to beginning of marker c line.
'c	Go to first non-blank character of marker c line.

Search for strings

/string	Search forward for string
?string	Search back for string
n	Search for next instance of string
N	Search for previous instance of string
%	Searches to beginning of balancing ( ) [ ] or { }
fc	Searches forward in current line to char
Fc	Searches backward in current line to char
tc	Searches forward in current line to character before char
Tchar	Searches backward in current line to character before char
?str	Finds in reverse for str
:set ic	Ignores case when searching
:set noic	Pays attention to case when searching
:n,ms/str1/str2/opt	Searches from n to m for str1; replaces str1 to str2; using opt-opt can be g for global change, c to confirm change (y to acknowledge, to suppress), and p to print changed lines
&	Repeats last :s command
:g/str/cmd	Runs cmd on all lines that contain str
:g/str1/s/str2/str3/	Finds the line containing str1, replaces str2 with str3
:v/str/cmd	Executes cmd on all lines that do not match str
,	Repeats, in reverse direction, last / or ? search command

Replace

The search and replace function is accomplished with the :s command. It is commonly used in combination with ranges or the :g command (below).

:s/pattern/string/flags	Replace pattern with string according to flags.
g	Flag - Replace all occurences of pattern
c	Flag - Confirm replaces.
&	Repeat last :s command

Regular Expressions

. (dot)	Any single character except newline
*	zero or more occurances of any character
[...]	Any single character specified in the set
[^...]	Any single character not specified in the set
\<	Matches beginning of word
\>	Matches end of word
^	Anchor - beginning of the line
$	Anchor - end of line
\<	Anchor - begining of word
\>	Anchor - end of word
$...$	Grouping - usually used to group conditions
\n	Contents of nth grouping
\	Escapes the meaning of the next character (e.g., \$ allows you to search for $)
\\	Escapes the \ character

[...] - Set Examples
[A-Z]	The SET from Capital A to Capital Z
[a-z]	The SET from lowercase a to lowercase z
[0-9]	The SET from 0 to 9 (All numerals)
[./=+]	The SET containing . (dot), / (slash), =, and +
[-A-F]	The SET from Capital A to Capital F and the dash (dashes must be specified first)
[0-9 A-Z]	The SET containing all capital letters and digits and a space
[A-Z][a-zA-Z]	In the first position, the SET from Capital A to Capital Z In the second character position, the SET containing all letters
[a-z]{m}	Look for m occurances of the SET from lowercase a to lowercase z
[a-z]{m,n}	Look for at least m occurances, but no more than n occurances of the SET from lowercase a to lowercase z

Regular Expression Examples
/Hello/	Matches if the line contains the value Hello
/^TEST$/	Matches if the line contains TEST by itself
/^[a-zA-Z]/	Matches if the line starts with any letter
/^[a-z].*/	Matches if the first character of the line is a-z and there is at least one more of any character following it
/2134$/	Matches if line ends with 2134
/$21\|35$/	Matches is the line contains 21 or 35 Note the use of ( ) with the pipe symbol to specify the 'or' condition
/[0-9]*/	Matches if there are zero or more numbers in the line
/^[^#]/	Matches if the first character is not a # in the line
Notes: 1. Regular expressions are case sensitive 2. Regular expressions are to be used where pattern is specified

Counts

Nearly every command may be preceded by a number that specifies how many times it is to be performed. For example, 5dw will delete 5 words and 3fe will move the cursor forward to the 3rd occurence of the letter e. Even insertions may be repeated conveniently with this method, say to insert the same line 100 times.

Ranges

Ranges may precede most "colon" commands and cause them to be executed on a line or lines. For example :3,7d would delete lines 3-7. Ranges are commonly combined with the :s command to perform a replacement on several lines, as with :.,$s/pattern/string/g to make a replacement from the current line to the end of the file.

:n,m	Range - Lines n-m
:.	Range - Current line
:$	Range - Last line
:'c	Range - Marker c
:%	Range - All lines in file
:g/pattern/	Range - All lines that contain pattern

Shell Functions

:! cmd	Executes shell command cmd; you can add these special characters to indicate:% name of current file# name of last file edited
!! cmd	Executes shell command cmd, places output in file starting at current line
:!!	Executes last shell command
:r! cmd	Reads and inserts output from cmd
:f file	Renames current file to file
:w !cmd	Sends currently edited file to cmd as standard input and execute cmd
:cd dir	Changes current working directory to dir
:sh	Starts a sub-shell (CTRL-d returns to editor)
:so file	Reads and executes commands in file (file is a shell script)
!Motion_cmd	Sends text from current position to Motion Command to shell command cmd
!}sort	Sorts from current position to end of paragraph and replaces text with sorted text

Files

:w file	Write to file
:r file	Read file in after line
:n	Go to next file
:p	Go to previous file
:e file	Edit file
!!program	Replace line with output from program

VI Settings

--noto

Note: Options given are default. To change them, enter type :set option to turn them on or :set nooptioni to turn them off.To make them execute every time you open VI, create a file in your HOME directory called .exrc and type the options without the colon (:) preceding the option
Set	Default	Description
:set ai	noai	Turns on auto indentation
:set all	--	Prints all options to the screen
:set ap	aw	Prints line after d c J m :s t u commands
:set aw	noaw	Automatic write on :n ! e# ^^ :rew ^} :tag
:set bf	nobf	Discards control characters from input
:set dir=tmp	dir = /tmp	Sets tmp to directory or buffer file
:set eb	noed	Precedes error messages with a bell
:set ed	noed	Precedes error messages with a bell
:set ht=	ht = 8	Sets terminal hardware tabs
:set ic	noic	Ignores case when searching
:set lisp	nolisp	Modifies brackets for Lisp compatibility.
:set list	nolist	Shows tabs (^l) and end of line ($)
:set magic	magic	Allows pattern matching with special characters
:set mesg	mesg	Allows others to send messages
:set nooption		Turns off option
:set nu	nonu	Shows line numbers
:set opt	opt	Speeds output; eliminates automatic RETURN
:set para=	para = LIlPLPPPQPbpP	macro names that start paragraphs for { and } operators
:set prompt	prompt	Prompts for command input with :
:set re	nore	Simulates smart terminal on dumb terminal
:set remap	remap	Accept macros within macros
:set report	noreport	Indicates largest size of changes reported on status line
:set ro	noro	Changes file type to "read only"
:set scroll=n	scroll = 11	set n lines for CTRL-d and z
:set sh=shell_path	sh = /bin/sh	set shell escape (default is /bin/sh) to shell_path
:set showmode	nosm	Indicates input or replace mode at bottom
:set slow	slow	Pospone display updates during inserts
:set sm	nosm	Show matching { or ( as ) or } is typed
:set sw=n	sw = 8	Sets shift width to n characters
:set tags=x	tags = /usr/lib/tags	Path for files checked for tags (current directory included in default)
:set term	$TERM	Prints terminal type
:set terse	noterse	Shorten messages with terse
:set timeout		Eliminates one-second time limit for macros
:set tl=n	tl = 0	Sets significance of tags beyond n characters (0 means all)
:set ts=n	ts = 8	Sets tab stops to n for text input
:set wa	nowa	Inhibits normal checks before write commands
:set warn	warn		Warns "no write since last change"
:set window=n	window = n	Sets number of lines in a text window to n
:set wm=n	wm = 0	Sets automatic wraparound n spaces from right margin.
:set ws	ws	Sets automatic wraparound n spaces from right margin.

Key Mapping

NOTE: Map allows you to define strings of VI commands. If you create a file called ".exrc" in your home directory, any map or set command you place inside this file will be executed every time you run VI. To imbed control characters like ESC in the macro, you need to precede them with CTRL-v. If you need to include quotes ("), precede them with a \ (backslash). Unused keys in vi are: K V g q v * = and the function keys. Example (The actual VI commands are in blue): :map v /I CTRL-v ESC dwiYou CTRL-v ESC ESC Description: When v is pressed, search for "I" (/I ESC), delete word (dw), and insert "You" (iYou ESC). CTRL-v allows ESC to be inserted
:map key cmd_seq	Defines key to run cmd_seq when pressed
:map	Displays all created macros on status line
:unmap key	Removes macro definition for key
:ab str string	When str is input, replaces it with string
:ab	Displays all abbreviations
:una str	Unabbreviates str

Other

~	Toggle upper and lower case
J	Join lines
nJ	Joins the next n lines together; omitting n joins the beginning of the next line to the end of the current line
.	Repeat last text-changing command
u	Undo last change (Note: u in combination with . can allow multiple levels of undo in some versions)
U	Undo all changes to line
;	Repeats last f F t or T search command
:N or :E	You can open up a new split-screen window in (n)vi and then use ^w to switch between the two.

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Basic Commands in VI

Click here for the Advanced VI commands