OSGi book summary part one

Summary for book "Die OSGI Service Platform-Eine Einführung mit Eclipse Equinox" link

The book is a good introduction to OSGi. It has 24 chapters, from OSGi introduction to OSGi and Equinox Standard Services. The book is divided in three part: part one: OSGi Framework, part two: OSGi Standard Services, part three: Equinox Services(Extensions)

Following chapters are discused in first part:
Bundles, Bundles lifcycles, Packages dependencies, OSGi Services, dynamic Services, Fragment Bundles, Security, Management of OSGi Service Platform, Packaging and Deployment


this blog summary the summary of the book:

* how to install Eclipse PDE (download eclipse-equinox-SDK-3.xxxx.zip)

* describe how OSGi work: bundles, layers, lifecycles, deployment, services, avaiable implementations(felix, equinox), example to start a http game services.


* Bundle Manifest have descriptive information about bundles, the manifest will be readed and interpreted by OSGi platform.
* Bundle-Classpath have locale paths
* Bundle-Activator is the start and stop point of a bundle with org.osgi.framework.BundleActivator
* BundleContext (parameter on start()/stop()), allow access to OSGi framework. Through context you can install new bundles, register listener, register and ask for services.

* Equinox console is a simpler Management Agent. You can ask for state of bundles and OSGi environment. A bundle has different states (installed, uninstalled, running, stoped)
* Activator Policies can change the behavior of bundles starts. (time, sequence, ressources). Lazy Activator set the bundle only start if other required him.
* It exists change of states with code too. (not only manifest-file)
* Bundle listener can notify you about state changes. Listener are registered with BundleContext.
* Bundle Cache save the states for persistence beyound the start()/stop() borders.

* For using other bundles you must explizit import/export you bundles in manifest-file.
* That is done with Export-Package and Import-Package labels.
* Required-Bundle specific the whole bundle. Import-Package only classes/packages. '*' import all class in a package.
* With Versioning you can specify which version of a same bundle the other bundle should use.
* With DynamicImport-Package you can import packages which doesn't exists yet.

* OSGi services are simple java objects (POJO Plain Old Java Objects). The services are registered to Service Registry with theirs class names. The services could quered by other bundles.
* The access to Services happen with ServiceReference and BundleContext
* On registry you can send some properties (which is a simple hash map)
* To get a reference: BundleContext.getServiceReferences() and the class name of service. Then you can use filter.
* With start leveln you can affect the start sequence of bundles.

* Sercice Tracker help you to work with one interface, independent from runtime/lifecycle. Tracker help dynamic react to services in/outgoing.
* ServiceTrackerCustomizer help you to react to different changes with call-back methods.
* Central OSGi Service Registry is the Whiteboard-Pattern and allow simple way the traditional listener-patern to replace.

* Fragments bundles expand the classpath of others bundles ( to avoid overloading of code/info for one bundle). It is a simple way to divide logic part from presentation(templates, languages).
* Fragmenst have no lifecycles (no Activators). manifest: Fragment-Host
* The Import/Export/Requirement information from Fragment Bundle will transfer to Host Bundle (which use the Fragment Bundle)
* Extension Bundles you can change the boot-classpath and expand it with additional features.

* Security in OSGi: local access can be setted to avoid execution in OSGI-INF/permissions.perm
* You can run only signed bundles or with certificates
* Conditional Permission Admin Service asign global authorization (Conditions)

* Management Agent implement an access to OSGi framework. For administrate framework from outside.
* It can be done by shell. or with programmatic.
* You can code your own commands with implement a CommandProvider with org.eclipse.osgi.framework.console.CommandProvider and register it to OSGi Service Registry.

* Plug-in Export Wizard is a simple facility to build bundles for extern world (and not only work with eclipse)
* For automatic build: ant4eclipse, Maven
* To start Eclipse Equinox: use org.eclipse.osgi_version.jar. Or start org.eclipse.core.runtime.adapptor.EclipseStarter from an Java application.
* With System properties or config.ini you can manipulate Equinox

Scala test

http://www.scalatest.org/getting_started_with_feature_spec

Python stuff

functions numbers

int(), long8), float(), round(), hex(), oct(), pow(), cmp()

s1+s2 merge
s1*n s1+s1+s1+s1+...

functions strings:
org(), chr(), str(), repr(), unicode(), len()

s.count(), s.encode(), s.endswith(), s.find(), s.isalnum(), s.iksalpha(), s.isdigi(), s.islower(), s.isspace(), s.join(), s.lstrip(), s.replace(), s.rfind(), s.rstrip(), s.split(), s.startswith(), s.strip(), s.swapcase()


List:
array=[1,2,3,4]
len(array)
array[1]="blub"
array[2]=["bla", [1,2,3], 'ups']

append(), extend(), count(), index(), insert(), remove(), pop(), reverse(), sort()


range()
range(4)
[0,1,2,3]
range(5,10,2]
[5,7,9]

Tuples
same as list but imutable

t1=(1,2,3)


indicies and slices

s[4:]
s[4:7]
s[:-7]
s[-4:]
s[:]
max(), min(), len()

a,b,c = [ 1, 2, 3 ]

del delete a varaible

a= 1
del a


assoziative lists, hash

h = { k:v, k2:v2, k3:v3 }
t={"peter":23450, "anna":39454, "blub":439549}
t["blub"]
items(), keys(), values(), has_key(), update()
t.has_key("anna")
len(), del()


None, type(), in-operator

if 2 in lists:
...
if not "a" in string:
...


Functions:

def p(n):
"bla bla, describe function for help"
for a in range(2,n):
...

p(3)


def fct(a, b="bla"):
...

fct(3, "lala")
fct(3)

several arguments with *

def h(g, *args):
for m in args:
...

h("bl", "blub", "abc", "dbc")


def h(**args):
if len(args==0): return
for n in args.keys():
print args[n]+" : "+ n

h(v1="blub", v2="aga")

def complexparameters(firma, delim="-", *address, **inventars):

def doNothing():
pass


functionale coding

add = lambda x,y: x+y
add(2,3)

map(ord, "string")
[115,116,114,...]

[ord(a) for a in "string"]

map(lambda x:x+1,(1,2,3))
map for tuple (1,2,3) x+1

def p(n):
for a in range(2,n):
if n%a == 0:
return 0
else:
return 1

filter(p, range(100))


reduce(function, collection)

a=5
exec("var" +str(a)+"="+str(a))
=> var5=5

docstrings:
def bla():
""" blal bla"""
...

bla.__doc__

Modules

JAVA stuff

read from input:

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String name = br.readLine();
int age = new Integer( br.readLine() ).intValue();

RUBY codes: code blocks and iterations

from "Ruby Cookbook" O'Reilly
for detailed information, look this book

[1,2,3].each { |i| puts i }

[1,2,3].each do |i|
  if i%2 == 0
    puts "="
  else
    puts "!"
  end
end

1.upto 3 do |x|   # same 1.upto(3)

1.upto(3) { |x| ... }   # ok
1.upto 3 { |x| ... }    # error


log = lambda { |str| puts "[LOG] #{str}" }
log.call("A test log message.")


{1=>2, 2=>4}.each { |k,v| puts "Key #{k}, value #{v}" }


def times_n(n)
  lambda { |x| x * n }
end

times_ten = times_n(10)
times_ten.call(5)        # => 50

circumference = times_n(2*Math::PI)
[1, 2, 3].collect(&circumference)
# => [6.28318530717959, 12.5663706143592, 18.8495559215388]

Clousure:
Every Ruby block is also a closure.

ceiling = 50
[1, 10, 49, 50.1, 200].select { |x| x <  ceiling }
# => [1, 10, 49]

the var celing is context depended.

Lambda and Proc

block = { |x| puts x }                  # error
block = lambda { |x| puts x }           # ok
block.call "bla bla!"


def my_lambda(&aBlock)   # a block in function parameters
  aBlock
end

b = my_lambda { puts "Hello World My Way!" }
b.call
b.class   # => Proc

aBlock = Proc.new { |x| puts x }
aBlock = proc { |x| puts x }
aBlock = lambda { |x| puts x }


add_lambda = lambda { |x,y| x + y }
add_lambda.call(4,5,6)  # ArgumentError: wrong number of arguments (3 for 2)

add_procnew = Proc.new { |x,y| x + y }
add_procnew.call(4,5,6)     # => 9

Yielding

def myfunc
  puts "1"
  yield
  puts "2"
  yield
end

myfunc("3")
# 1
# 3
# 2
# 3


def repeat(n)
  if block_given?
    n.times { yield }
  else
    raise ArgumentError.new("I can't repeat a block you don't give me!")
  end
end

repeat(4) { puts "Hello." }
# Hello.
# Hello.
# Hello.
# Hello.

repeat(4)
# ArgumentError: I can't repeat a block you don't give me!

read file in Scala

read file in scala:

for (file <- new File("/var/log/").listFiles) {

list a directory

if (!file.isDirectory) {

ask is file not a directory

simple print out of a file

import scala.io.Source  
  
for {  
  (line) <- Source.fromFile("bla.txt").getLines  
} print(line)  

read a file in an iterator

scala> val lines = scala.io.Source.fromFile("/var/log/syslog")
lines: scala.io.Source = non-empty iterator

scala> lines
res5: scala.io.Source = non-empty iterator

read a file in a string

val lines = scala.io.Source.fromFile("/var/log/syslog").mkString

// for utf-8 encoding
val lines = scala.io.Source.fromFile("file.txt", "utf-8").getLines.mkString

or you can use Java API

val os = new BufferedOutputStream(new FileOutputStream("gen/" + file.getName))

Challenge: pattern syslog

Challenge:

filtern some patern in file /var/log/syslog
and print it out


Shell:

fgrep usb /var/log/syslog

Java:

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;


public class JavaFilters {
 public static void main(String[] args) {
  String path="/var/log/syslog";
  try {
   BufferedReader input =  new BufferedReader(new FileReader(path));
   
   String line;
   try {
    Pattern p = Pattern.compile("dhclient");
    while (( line = input.readLine()) != null){
     Matcher m = p.matcher(line);
     if(m.find())
      System.out.println("found:: "+line);
    }
   } catch (IOException e) {
    e.printStackTrace();
   }
  } catch (FileNotFoundException e) {
   e.printStackTrace();
  }
 }
}

Scala:

import scala.io.Source
import java.util.regex._

var p = Pattern.compile("usb")

for ( line <- Source.fromFile("/var/log/syslog").getLines ){  
  var m = p.matcher(line);
  if( m.find ) 
    print("found::" + line)
} 

Perl:

#!/usr/bin/perl

open(IN, "/var/log/syslog") or die "canot open file: $!";

@lines = <IN>;
close IN;

foreach $line(@lines) {
  if( $line =~ /dhclient/) {
    print "found:: $line";
  }
}

Ruby:

#!/usr/bin/ruby

file = File.new("/var/log/syslog", "r") or die "canot open file"

while (line = file.gets)
  if ( line =~ /usb/ )
    print "found:: "+line
  end
end

Python:

#!/usr/bin/python

try: 
  f = open('/var/log/syslog', 'r')

  for line in f.readlines():
    if( "usb" in line ): 
      print("found:: %s"%line)

except: 
  print "error in file"

PHP:

<?php
$file = "/var/log/syslog";
if (file_exists($file)) {
  $lines = file($file);
  foreach ($lines as $line_num => $line) 
    if( preg_match("/usb/", $line) ) 
      echo "$line";
}
?>

C:

#include 
#include 
#include 
#include 
#include 

FILE *file = NULL; 

int main(int argc, char **argv)
{
  char line[1024];
  int err;
  char err_str[200];
  char results[500];
  
  regex_t preg;
  regmatch_t pmatch[100];
  
  if( (regcomp(&preg, argv[1], 0)) != 0)  {
    printf("regcomp error\n");
    return -1;
  }
  
  if((file = fopen("/var/log/syslog", "r")) != NULL) {
    while (!feof(file)){
      fgets(line, 1024, file);

      if( regexec(&preg, line, preg.re_nsub, pmatch, 0) == 0)  {
          printf("found:: %s", line);
      }  
    }
  }

  regfree(&preg);
  return 0;
}

learning Scala 3

this tutorial based on:
http://www.artima.com/scalazine/articles/steps.html

def max(x: Int, y: Int): Int = if (x < y) y else x

def max(x: Int, y: Int) -> define a function, with 2 parameters (integer)
: Int -> return is integer.
if (x < y) y else x -> function body

scala> def greet() = println("Hello, world!")
greet: ()Unit

scala> greet()
Hello, world!

scala> greet
Hello, world!

greet save a Unit -> a function

args.foreach(arg => println(arg))
args.foreach((arg: String) => println(arg))
args.foreach(println)

for (arg <- args)
  println(arg)


scala> for (i <- 0 to 5)
     | println(i)
0
1
2
3
4
5

val greetStrings: Array[String] = new Array[String](3)

create an array with 3 strings

greetStrings(0) = "Hello"
greetStrings(1) = ", "
greetStrings(2) = "world!\n"

important indexes are in brakes () not square brackets[]

for (i <- 0 to 2)
  print(greetStrings(i))

learning Scala 2

this tutorial based on:
http://www.thomasknierim.com/104/scala/scala-tutorial-1/
http://www.thomasknierim.com/104/scala/scala-tutorial-2/
http://www.thomasknierim.com/104/scala/scala-tutorial-3/

object Hello {
  def main(args: Array[String]) {
    for(val arg: String <- args)
      System.out.println("Hello, " + arg + "!");
  }
}

for(val arg: String <- args) -> an array into each arg as String

similar: args.foreach(arg => println("Hello" + arg + "!"))
"=>" that can be read “with a given argument this do that”

args.foreach(println)

var decrease = (x: Int) => x - 1
decrease(11)

(x: Int) => x - 1 -> anonymous function declaration


var decrease = (x: Int) => x – something

something is not defined yet. decrease is depend on context -> clousure

In terms of computer science, a closure is a function that is evaluated and whose result depend on an outer context.

something = 10
decrease(100)


some examples for higher-order functions

scala> List("alpha", "beta", "crash").map(
  p => p.substring(0,1))
res0: List[java.lang.String] = List(a, b, c)
 
scala> List(1, 2, 3) map (_ * 2)
res1: List[Int] = List(2, 4, 6)
 
scala> List("Tango", "Mango", "Bobo", "Gogo")
    map (_.endsWith("go"))
res2: List[Boolean] = List(true, true, false, true)

List("alpha", "beta", "crash") -> create a list

map() -> map each list element to some condition/function

p => p.substring(0,1) p is the element p.substring(0,1) is the function

_ -> ist the element (similar to perl $_ )
(_*2) is equivalent to (i => i * 2)

object FileMatcher {
 
  private val filesHere=(new java.io.File(".")).listFiles
 
  private def filesMatching(matcher: String => Boolean)=
    for (file <- filesHere; if matcher(file.getName))
      yield file
 
  def filesEnding(query: String)=
    filesMatching(_.endsWith(query))
  def filesContaining(query: String)=
    filesMatching(_.contains(query))
  def filesRegex(query: String)=
    filesMatching(_.matches(query))
}
 
object Main {
  def main(args: Array[String]) {
    val query = args(0);
    var matchingFiles = FileMatcher.filesEnding(query)
    matchingFiles = FileMatcher.filesContaining(query)
    matchingFiles = FileMatcher.filesRegex(query)
  }
}

let look:

scala> (new java.io.File(".")).listFiles
res2: Array[java.io.File] = Array(./FrenchDate$.class, ./FrenchDate.class, ./Complex.scala, ./s1.class, ./s1$.class, ./FrenchDate.scala, ./Timer$$anonfun$main$1.class, ./s1.scala, ./Timer$.class, ./Hello.class, ./ComplexNumbers.class, ./Hello.scala, ./Hello$$anonfun$main$1.class, ./blog_scala2.txt, ./Timer.class, ./Hello$.class, ./Complex.class, ./blog_scala1.txt, ./ComplexNumbers.sca...

new java.io.File(".") use the java api and create a file object File.
listFiles is the same as listFiles() in java. in scala you don't need brakes.

for (file <- filesHere; if matcher(file.getName))
yield file

iterate all filesHere (files in path "."). if name match to query, yield the file. the file get in an array.

scala> var matchingFiles = FileMatcher.filesEnding(query)
matchingFiles: Array[java.io.File] = Array(./Complex.scala, ./FrenchDate.scala, ./s1.scala, ./Hello.scala, ./Main.scala, ./ComplexNumbers.scala, ./Timer.scala)

def filesEnding(query: String)=
    filesMatching(_.endsWith(query))

define different functions


filesMatching(matcher: String => Boolean)

define the function with a matcher(String) which return Boolean

learning Scala

This tutorial based on:
http://www.scala-lang.org/docu/files/ScalaTutorial.pdf
http://www.thomasknierim.com/77/scala/scala-tutorial-2/



write a file s1.scala

object HelloWorld {
  def main(args: Array[String]) {
    println("Hello, world!")
  }
}

object -> declare a static singleton object
args: Array[String] -> a variable args as Array of Strings

compile and execute

$ scalac s1.scala 
$ ls
s1.class  s1$.class  s1.scala

you get created standard java class files, but you must use java interpreter with setted parameters.

$ java s1
Exception in thread "main" java.lang.NoClassDefFoundError: scala/ScalaObject
 at java.lang.ClassLoader.defineClass1(Native Method)
....

$ file /usr/bin/scala
$ /usr/bin/scala: POSIX shell script text executable
$ cat /usr/bin/scala
#!/bin/sh

JAVA_DIR=/usr/share/java
LIB_CLASSPATH=$JAVA_DIR/scala-library.jar:$JAVA_DIR/scala-compiler.jar:$JAVA_DIR/jline.jar

exec ${JAVACMD:=java} ${JAVA_OPTS:=-Xmx256M -Xms16M} \
  -Xbootclasspath/a:$LIB_CLASSPATH \
  -classpath .:$CLASSPATH:$LIB_CLASSPATH \
  scala.tools.nsc.MainGenericRunner \
  "$@"

$ scala s1
hallo

As you can see, the scala executable is a simple shell script, which start the java virtual machine with specific parameters and the scala library.


Create Date.scala

import java.util.{Date, Locale}
import java.text.DateFormat
import java.text.DateFormat._
object FrenchDate {
  def main(args: Array[String]) {
    val now = new Date
    val df = getDateInstance(LONG, Locale.FRANCE)
    println(df format now)
  }
}

import java.util.{Date, Locale}	import Date and Locale from java.util
import java.text.DateFormat._	DateFormat._ is similar to DateFormat.* in java
val	declare an inmutable variable
val now = new Date	simmilar to "Date now = new Date();" in java
println(df format now)	"df format now" is similar to "df.format(now)"

---

In scala is everything an object. There is no primitive datatypes (that is similar to ruby).

Because scala based on functional programming functions are objects too.

object Timer {

  def oncePerSecond(callback: () => Unit) {
    while (true) { callback(); Thread sleep 1000 }
  }

  def timeFlies() {
    println("time flies like an arrow...")
  }

  def main(args: Array[String]) {
    oncePerSecond(timeFlies)
  }
}

with functions as object you can very simple code a callback.

timeFlies()	our callback function.
callback: () => Unit	parameter for a function. ()=>Unit is the type of all functions which take no arguments and return nothing.
Thread sleep 1000	is similar to Thread.sleep(1000)

rather the function timeFlies() you can use anonymous functions ala:

oncePerSecond(() => println("time flies like an arrow..."))

"() => code" declare an anonymous function

---

Clases:

class Complex(real: Double, imaginary: Double) {
   def re() = real
   def im() = imaginary
}

define class Complex with two arguments,
def re() and im() are getters. return type of these two methods is not given explicitly

object ComplexNumbers {
  def main(args: Array[String]) {
    val c = new Complex(1.2, 3.4)
    println("imaginary part: " + c.im())
  }
}

if you have no arguments in function, write: def re = real

class Complex(real: Double, imaginary: Double) {
  def re = real
  def im = imaginary
  override def toString() =
    "" + re + (if (im < 0) "" else "+") + im + "i"
}

class Complex(real: Double, imaginary: Double) -> primary constructor, which is part of the class declaration
override -> for overriding functions

(if (im < 0) "" else "+") have you see it ;)

class Rational(numerator: Int, denominator: Int) {
 
  require(denominator != 0)
 
  private val gcd = greatestCommonDivisor(numerator.abs,
    denominator.abs)
  val n = numerator / gcd
  val d = denominator / gcd
 
  def this(n: Int) = this(n, 1)
 
  private def greatestCommonDivisor(a: Int, b: Int): Int =
  if (b == 0) a else greatestCommonDivisor(b, a % b)
 
  def + (that: Rational): Rational =
  new Rational(n * that.d + d * that.n, d * that.d)
 
  def - (that: Rational): Rational =
  new Rational(n * that.d - d * that.n, d * that.d)
 
  def * (that: Rational): Rational =
  new Rational(n * that.n, d * that.d)
 
  def / (that: Rational): Rational =
  new Rational(n * that.d, d * that.n)
 
  override def toString = n + "/" + d
}

require(denominator != 0) -> look that variable is not null, throw exception


def this(n: Int) = this(n, 1) -> create from Rational(2) -> Rational(2,1)

you can see +-*/ are objects functions, which can be simple overrided

bashing

test -x $BLA || exit 5

find /proc -type s
ls -Rl /proc/[0-9]* | grep ^s

some commands

lpr -Plp Datei # datei ausdrucken

fuser -k /dev/lp0 # alle dienste die den /dev/lp0 benutzen toeten
#/dev/usb/lp0

scsi-scanner /dev/sg0

set -o nochlobber

git-rev-tree --bisect ^good1 ^good2 bad > git/refs/headers/tryN
git checkout tryN
^goodx > v2.6.12 bad > master


movw%bx, (%rsi) <-> recvfrom()


/usr/sbin/snort -b -m 027 -D -N -c /etc/snort/snort.conf -d -u snort -g snort -i eth1


iptables -A INPUT -ptcp -s PVT_IP_HERE -d 0/0


wget -p nur inhalt,
wget -r -np nur unterverzeichniss, nicht von root an

make kpkg, create a linux kernel image

export CONCURRENCY_LEVEL=6

time make-kpkg --initrd --append-to-version 1 --revision 1 kernel_image modules

trying Scala ... 3

List:

scala> var lst = List(1, 7, 2, 8, 5, 6, 3, 9, 14, 12, 4, 10)
res29: List[Int] = List(1, 7, 2, 8, 5, 6, 3, 9, 14, 12, 4, 10)


scala> def odd(inLst:List[Int]):List[Int]={
| if(inLst==Nil) Nil
| else if(inLst.head%2==1) inLst.head::odd(inLst.tail)
| else odd(inLst.tail)
| }
odd: (List[Int])List[Int]


def define a function/method
od() name
inLst:List[Int] => inLst parameter name with a List type of Integers
:List[Int] return a List of Integers
Nil similar to none, None, null, void
inLst.head first element
inLst.tail all other elements after first element



scala> odd(lst)
res32: List[Int] = List(1, 7, 5, 3, 9)


trying Scala ... 2


scala> val try1=if (1==2) 8 else 9
try1: Int = 9

scala> var total=18
total: Int = 18
scala> while(total < 17) total+=3
scala> total
res15: Int = 18

scala> for(i <- 1 to 4) println("hi five")
hi five
hi five
hi five
hi five

scala> for(i <- 1 until 5 ; j <- 1 to 3) println(i,j)
(1,1)
(1,2)
(1,3)
(2,1)
(2,2)
(2,3)
(3,1)
(3,2)
(3,3)
(4,1)
(4,2)
(4,3)

scala> for(c<-"hello")println(c)
h
e
l
l
o


hex, octal, bin is the same as in java


scala> val abyte: Byte = 27
abyte: Byte = 27


scala> var chr='A'
chr: Char = A
scala> chr=5
chr: Char =
scala> chr=66
chr: Char = B


define functions:

scala> def max(x: Int, y: Int): Int = {
| if (x > y) x
| else y
| }
max: (Int,Int)Int

scala> max(6,7)
res22: Int = 7

scala> max(3.6, 4)
:6: error: type mismatch;
found : Double(3.6)
required: Int
max(3.6, 4)



define a class


scala> class Point {
| var x=0
| var y=0
| }
defined class Point


scala> val p=new Point
p: Point = Point@18b62e0

scala> p.x=3
scala> p.y=4


scala> class Point( ix:Int,iy:Int){
| var x=ix
| var y=iy
| def vectorAdd(newpt:Point):Point={
| new Point(x+newpt.x,y+newpt.y)
| }
| }
defined class Point

scala> val p1=new Point(3,4)
p1: Point = Point@75455c
scala> val p2=new Point(7,2)
p2: Point = Point@1ba3523
scala> val p3=p1.vectorAdd(p2)
p3: Point = Point@1095c6c
scala> println(p3.x,p3.y)
(10,6)


scala> class Point( ix:Int,iy:Int){
| var x=ix
| var y=iy
| def +(newpt:Point):Point={
| new Point(x+newpt.x,y+newpt.y)
| }
| def -(newpt:Point):Point={
| new Point(x-newpt.x,y-newpt.y)
| }
| override def toString="Point("+x+","+y+")"
| }
defined class Point

scala> val p1=new Point(3,4)
p1: Point = Point(3,4)
scala> val p2=new Point(7,2)
p2: Point = Point(7,2)
scala> val p3=new Point(-2,2)
p3: Point = Point(-2,2)

scala> val p4=p1+p2-p3
p4: Point = Point(12,4)
scala> println(p4.x,p4.y)
(12,4)


there is no switch -> use match

scala> def decode(n:Int){
| n match {
| case 1 => println("One")
| case 2 => println("Two")
| case 5 => println("Five")
| case _ => println("Error")
| }
| }
decode: (Int)Unit











trying Scala ...

install scala, and type scala in console ;)


scala> 4/3.0
res5: Double = 1.3333333333333333

scala> 4/0
java.lang.ArithmeticException: / by zero
at .(:5)
at .()
at RequestResult$.(:3)
at RequestResult$.()
at RequestResult$result()
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAcce...

scala> var a=3
a: Int = 3

scala> a
res7: Int = 3

scala> a=5
a: Int = 5


scala> val b=3
b: Int = 3

scala> b
res10: Int = 3

scala> b=5
<console>:5: error: reassignment to val
b=5


var and val define variables, val is immutable

For printing is here
Ascala> println(b)
3

operators and control sturctures (if, else, ...) are the same as in java.


scala> val isBook = 6>=3
isBook: Boolean = true

scala> val price=16
price: Int = 16

scala> val vol=10
vol: Int = 10

scala> val sale=if (isBook)price*vol else price/vol
sale: Int = 160

scala> sale
res13: Int = 160


trying Scala

Tutorials: http://www.simplyscala.com/

Book: http://programming-scala.labs.oreilly.com/

further info from http://www.scala-lang.org/

http://www.scala-lang.org/node/1305

RCPLinAdmin

RCPLinAdmin is in planing,

should be an universal admin management tool for linux local/ssh writed in RCP/Eclipse.

http://sites.google.com/site/rcplinadmin