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  • apache-memory-hacker-linux

    - by bibhudatta
    When we start the linux system it take only 435mb memory and it is 4GB memory server. When we start the httpd services it take 1000mb and outmatically it take all the memory and the server crase. even we stop the apache just it release 200mb memory. What will be the problem Can any one tell me what these hacker are doing. I see they are goinging some hit to my apache by some but I thing they are doing from this system. Below is the log. Please help me out for this. [root@host ~]# tail -20 /var/log/httpd/dostizone.com-combined.log 180.76.5.143 - - [14/Nov/2011:02:30:16 +0530] "GET /blogs/10248/209403/nfl-panties-since-the-quality-of HTTP/1.1" 403 2298 "-" "Mozilla/5.0 (compatible; Baiduspider/2.0; +http://www.baidu.com/search/spider.html)" 180.76.5.88 - - [14/Nov/2011:02:30:31 +0530] "GET /blogs/815/158725/new-jersey-attorney-search HTTP/1.1" 403 2290 "-" "Mozilla/5.0 (compatible; Baiduspider/2.0; +http://www.baidu.com/search/spider.html)" 220.181.108.186 - - [14/Nov/2011:02:30:32 +0530] "GET / HTTP/1.1" 403 5043 "-" "Mozilla/5.0 (compatible; Baiduspider/2.0; +http://www.baidu.com/search/spider.html)" crawl-66-249-67-137.googlebot.com - - [14/Nov/2011:02:30:20 +0530] "GET /blogs/805/11279/supra-suprano-high-shoes HTTP/1.1" 200 30642 "-" "Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)" crawl-66-249-68-51.googlebot.com - - [14/Nov/2011:02:30:37 +0530] "GET /blogs/10514/215084/oakland-raiders-sweatpants-tags HTTP/1.1" 403 2297 "-" "Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)" 220.181.94.237 - - [14/Nov/2011:02:30:12 +0530] "GET /profile/8509 HTTP/1.1" 200 236894 "-" "Sogou web spider/4.0(+http://www.sogou.com/docs/help/webmasters.htm#07)" 220.181.94.237 - - [14/Nov/2011:02:30:43 +0530] "GET /mode-switch?return_url=%2Fblogs%2F8529%2F160217%2Fclimate-jordan-6 HTTP/1.1" 302 1 "-" "Sogou web spider/4.0(+http://www.sogou.com/docs/help/webmasters.htm#07)" crawl-66-249-68-51.googlebot.com - - [14/Nov/2011:02:30:44 +0530] "GET /blogs/390/61573/blackhawk-jerseys-from-the-you HTTP/1.1" 403 2293 "-" "SAMSUNG-SGH-E250/1.0 Profile/MIDP-2.0 Configuration/CLDC-1.1 UP.Browser/6.2.3.3.c.1.101 (GUI) MMP/2.0 (compatible; Googlebot-Mobile/2.1; +http://www.google.com/bot.html)" 124.115.0.159 - - [14/Nov/2011:02:30:24 +0530] "GET /blogs/693/46081/application/modules/Hecore/externals/scripts/core.js HTTP/1.1" 200 26869 "http://dostizone.com/blogs/693/46081/thomas-sabo-charms-hot-chilli" "Sosospider+(+http://help.soso.com/webspider.htm)" 124.115.0.159 - - [14/Nov/2011:02:30:24 +0530] "GET /blogs/693/46081/application/modules/Activity/externals/scripts/core.js HTTP/1.1" 200 26873 "http://dostizone.com/blogs/693/46081/thomas-sabo-charms-hot-chilli" "Sosospider+(+http://help.soso.com/webspider.htm)" 124.115.0.159 - - [14/Nov/2011:02:30:24 +0530] "GET /blogs/693/46081/application/modules/Hecore/externals/scripts/imagezoom/core.js HTTP/1.1" 200 26899 "http://dostizone.com/blogs/693/46081/thomas-sabo-charms-hot-chilli" "Sosospider+(+http://help.soso.com/webspider.htm)" 180.76.5.153 - - [14/Nov/2011:02:30:50 +0530] "GET /blogs/10252/212268/cleveland-browns-authentic-jerse HTTP/1.1" 403 2298 "-" "Mozilla/5.0 (compatible; Baiduspider/2.0; +http://www.baidu.com/search/spider.html)" crawl-66-249-68-51.googlebot.com - - [14/Nov/2011:02:30:51 +0530] "GET /blogs/741/46260/chocolate-ugg-women-boots-1873 HTTP/1.1" 403 2293 "-" "SAMSUNG-SGH-E250/1.0 Profile/MIDP-2.0 Configuration/CLDC-1.1 UP.Browser/6.2.3.3.c.1.101 (GUI) MMP/2.0 (compatible; Googlebot-Mobile/2.1; +http://www.google.com/bot.html)" 124.115.1.7 - - [14/Nov/2011:02:30:40 +0530] "GET /blogs/682/97454/swarovski-jewellry-sale-articles HTTP/1.1" 200 25770 "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)" crawl-66-249-68-51.googlebot.com - - [14/Nov/2011:02:30:56 +0530] "GET /blogs/779/60941/players-a-to-z-michael-cuddyer HTTP/1.1" 403 2293 "-" "SAMSUNG-SGH-E250/1.0 Profile/MIDP-2.0 Configuration/CLDC-1.1 UP.Browser/6.2.3.3.c.1.101 (GUI) MMP/2.0 (compatible; Googlebot-Mobile/2.1; +http://www.google.com/bot.html)" crawl-66-249-68-51.googlebot.com - - [14/Nov/2011:02:31:01 +0530] "GET /blogs/469/58551/chicago-bears-news-there-exist HTTP/1.1" 403 2293 "-" "SAMSUNG-SGH-E250/1.0 Profile/MIDP-2.0 Configuration/CLDC-1.1 UP.Browser/6.2.3.3.c.1.101 (GUI) MMP/2.0 (compatible; Googlebot-Mobile/2.1; +http://www.google.com/bot.html)" 220.181.94.237 - - [14/Nov/2011:02:30:54 +0530] "GET /blogs/8529/160217/climate-jordan-6 HTTP/1.1" 200 30750 "-" "Sogou web spider/4.0(+http://www.sogou.com/docs/help/webmasters.htm#07)" 180.76.5.59 - - [14/Nov/2011:02:31:05 +0530] "GET /blogs/815/158197/cheap-calgary-flames-jerseys HTTP/1.1" 403 2292 "-" "Mozilla/5.0 (compatible; Baiduspider/2.0; +http://www.baidu.com/search/spider.html)" crawl-66-249-68-51.googlebot.com - - [14/Nov/2011:02:31:06 +0530] "GET /mode-switch?return_url=%2Fblogs%2F387%2F45679%2Fhandbag-louis-vuitton-judy-mm-m4 HTTP/1.1" 403 2258 "-" "SAMSUNG-SGH-E250/1.0 Profile/MIDP-2.0 Configuration/CLDC-1.1 UP.Browser/6.2.3.3.c.1.101 (GUI) MMP/2.0 (compatible; Googlebot-Mobile/2.1; +http://www.google.com/bot.html)" crawl-66-249-67-137.googlebot.com - - [14/Nov/2011:02:31:10 +0530] "GET /public/temporary/c83b731ecc556d7fd1a7732d9ac16ed6.png HTTP/1.1" 404 2305 "-" "Googlebot-Image/1

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  • How to use imported css styles in GWT correctly

    - by Eduard Wirch
    Imagine you created the following simple widget with UiBinder: <!DOCTYPE ui:UiBinder SYSTEM "http://dl.google.com/gwt/DTD/xhtml.ent"> <ui:UiBinder xmlns:ui="urn:ui:com.google.gwt.uibinder" xmlns:g="urn:import:com.google.gwt.user.client.ui"> <ui:style type="my.package.Widget1.Widget1Style"> .childWidgetStyle { border-width: 1px; border-style: dotted; } </ui:style> <g:TextArea styleName="{style.childWidgetStyle}"/> </ui:UiBinder> package my.package; // some imports here public class Widget1 extends Composite { private static Widget1UiBinder uiBinder = GWT.create(Widget1UiBinder.class); interface Widget1UiBinder extends UiBinder<Widget, Widget1> { } public interface Widget1Style extends CssResource { String childWidgetStyle(); } @UiField TextArea textArea; public Widget1(String text) { initWidget(uiBinder.createAndBindUi(this)); textArea.setText(text); } } Than you use this simple widget in another (parent) widget you created: <!DOCTYPE ui:UiBinder SYSTEM "http://dl.google.com/gwt/DTD/xhtml.ent"> <ui:UiBinder xmlns:ui="urn:ui:com.google.gwt.uibinder" xmlns:g="urn:import:com.google.gwt.user.client.ui"> <ui:style> .parentWidgetStyle .childWidgetStyle { margin-bottom: 10px; } </ui:style> <g:VerticalPanel ui:field="listPanel" addStyleNames="{style.parentWidgetStyle}" /> </ui:UiBinder> package my.package; // imports go here public class ParentWidget extends Composite { private static ParentWidgetUiBinder uiBinder = GWT.create(ParentWidgetUiBinder.class); interface ParentWidgetUiBinder extends UiBinder<Widget, ParentWidget> { } @UiField VerticalPanel listPanel; public ParentWidget(final String... texts) { initWidget(uiBinder.createAndBindUi(this)); for (final String text : texts) { final Widget1 entry = new Widget1(text); listPanel.add(entry); } } } What you want to achieve is to get some margin between the Widget1 entries in the list using css. But this won't work. Because GWT will obfuscate the css names. And the obfuscated name for .childWidgetStyle in ParentWidget will be different from the .childWidgetStyle in Widget1. The resulting css will look similar to this: .G1unc9fbE { border-style:dotted; border-width:1px; } .G1unc9fbBB .G1unc9fDa { margin-bottom:10px; } So the margin setting wont apply. How do I do this correctly?

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  • Movilidad y el modelo de computación en la nube como el actual paradigma tecnológico

    Movilidad y el modelo de computación en la nube como el actual paradigma tecnológico En este programa presentaremos una visión general de las oportunidades tecnológicas que favorecen la generación de emprendimientos regionales desde el equipo de relaciones para desarrolladores de la región de sur de Latinoamérica. Trataremos escenarios tecnológicos y principalmente el impacto de la movilidad y el modelo de computación en la nube, finalmente analizaremos las oportunidades más importantes junto a diversos referentes regionales. Tecnología, desafíos, opiniones y todo el ecosistema representado por la pasión y el talento regional. From: GoogleDevelopers Views: 0 0 ratings Time: 00:00 More in Education

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  • SEM/SEO tasks doubts

    - by Josemalive
    Hello, Actually i think that i have an strong knowledge of SEO, but im having some doubts about the following: I will have to increase the position in Google of certain product pages of a company in the next months. I supposed that not only will be sufficient the following tasks: Improve usability of those pages. Change the pages title. Add meta description and keywords. Url's in a REST way. 301's http header to dont lose page rank for the new URLS Optimizing content for Google. Configure links of the website (follow and no follow attributes) Get more inbounds links (Link building tasks). Create RSS. Put main website in Twitter (using twitter feed) using the RSS. Put main website in Facebook. Create a Youtube channel. Invest in Adwords. Invest in other online advertising companies. Use sitemap.xml and Google Webmaster tools. Use Google Trends to analyze the volume of searches of certain keywords. Use Google Analytics to analyze weak points and good points of your site, and find new oportunities in keywords. Use tools to find new keywords related with your content. Do you have some internet links, or knowledge about all the tasks that a SEO Expert should do? Could you share some knowledge about what kind of business could be do with another companies (B2B) to increase the search engine position of those product pages. Do you know more tecniques about how to get more inbound links? (i only know the link interchange) Thanks in advance. Best Regards. Jose.

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  • python protobufs - avoid the install step ?

    - by orion elenzil
    i'm writing a small python utility which will be consumed by moderately non-technical users and which needs to interface w/ some protobufs. ideally, i would like the only prerequisites to using this on a local machine to be: have python installed * have an SVN checkout of the repository * run a simple bash script to build the local proto .py definitions * run "python myutility" i'm running into trouble around importing descriptor_pb2.py, tho. i've seen Why do I see "cannot import name descriptor_pb2" error when using Google Protocol Buffers? , but would like to avoid adding the additional prerequisite of having run the proto SDK installer. i've modified the bash script to also generate descriptor_pb2.py in the local heirarchy, which works for the first level of imports from my other _pb2.py files, but it looks like descriptor_pb2.py itself tries to import descriptor_pb2 can't find it: $ python myutility.py Traceback (most recent call last): File "myutility.py", line 4, in <module> import protos.myProto_pb2 File "/myPath/protos/myProto_pb2.py", line 8, in <module> from google.protobuf import descriptor_pb2 File "/myPath/google/protobuf/descriptor_pb2.py", line 8, in <module> from google.protobuf import descriptor_pb2 ImportError: cannot import name descriptor_pb2 my local folder looks like: * myutility.py * google/ * protobuf/ * descriptor.py * descriptor_pb2.py * protos * myProto_ob2.py also, i'm a python n00b, so it's possible i'm overlooking something obvious. tia, orion

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  • Does Safari have a timeout issue?

    - by woodysapsucker
    I have a website that works fine in Firefox and IE but never finishes loading in Safari 4.0.4. The live website loads a menu then loads a Google map. Using Safari, the Google map never loads. I have a test website on the same server that uses the exact same code for loading a Google map and Safari can load the map (this is the one that won't load on my live web). This test website does not have the menu - only the Google map. In both cases (live and test) the main web page calls a loadmap.js file. I've been pulling everything apart to try to identify why Safari won't finish loading. Has anyone run across any problems/solutions with Safari that may help me find a resolution to this problem?

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  • Chrome Apps + Native Client

    Chrome Apps + Native Client Did you know that you can use Native Client inside a Chrome App? Join +John Mccutchan and +Pete LePage as they introduce Native Client Acceleration Modules (NaCl AM) which expose C++ libraries to JavaScript programs. NaCl AMs can, be used for bulk data processing (compression, encryption) but they also work well in interactive applications that require low latency. We'll explain how to build a NaCl Acceleration Module and demo a Bullet Physics engine running inside a Chrome App with a NaCl AM interacting with an HTML and JavaScript UI using three.js. We'll be live on Tuesday December 11th at at 9am PT, showing you code, samples and answering your questions. From: GoogleDevelopers Views: 0 0 ratings Time: 45:00 More in Science & Technology

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  • The polls are closed!!

    Greetings Everyone, This is just a quick note to let you know that the election for the two OpenSocial Board Community Representatives is now officially closed. We will...

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  • Look ma, no plugin!

    The new crop of HTML5 web browsers are capable of some pretty amazing things, and several of our engineers decided to take some 20% time to see how...

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  • Eclipse Error: java.net.SocketException: Broken pipe How to Solve ?

    - by Vaibhav Bhalke
    Hello Everybody I am using GWT2.0.1,when I am running web application then I get following error message on Console. after removing error from error log still same message occur as well as restarting eclipse_galileo.To solve this problem i want to restart machine. Each time this message comes on console,then i need to restart m/c I there any way to solve this problem ? please provide best solution? ASAP. Exception in thread "Code server for Dealelephant from Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.17) Gecko/2010010604 Ubuntu/9.04 (jaunty) Firefox/3.0.17 on http://127.0.0.1:8888/Dealelephant.html?gwt.codesvr=127.0.0.1:9997 @ Ci%#*k,XE'=JH,|~" com.google.gwt.dev.shell.BrowserChannel$RemoteDeathError: Remote connection lost at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:391) at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:222) at java.lang.Thread.run(Thread.java:619) Caused by: java.net.SocketException: Broken pipe at java.net.SocketOutputStream.socketWrite0(Native Method) at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92) at java.net.SocketOutputStream.write(SocketOutputStream.java:136) at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:65) at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:123) at java.io.DataOutputStream.flush(DataOutputStream.java:106) at com.google.gwt.dev.shell.BrowserChannel$ReturnMessage.send(BrowserChannel.java:1341) at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:388) ... 2 more Hope for Best co-operation Thank you in advance

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  • GDL Presents: Women Techmakers with Pixel Qi

    GDL Presents: Women Techmakers with Pixel Qi Jean Wang sits down with 2011 Anita Borg "Woman of Vision" Award for Innovation winner Mary Lou Jepsen of Pixel Qi to discuss overcoming technical challenges in hardware, drawing on Mary Lou's experience leading the engineering and architectural design of the $100 laptops that inspired the One Laptop Per Child (OLPC) organization. Hosts: Jean Wang - Lead Hardware Engineer for Project Glass | Vivian Cromwell - Manager, Global Chrome Developer Relations Guest: Mary Lou Jepsen - CEO and Founder, Pixel Qi From: GoogleDevelopers Views: 0 0 ratings Time: 01:00:00 More in Science & Technology

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  • Authlogic OpenID: Fetching E-Mail from Provider.

    - by Shripad K
    This is a really weird problem: I have set up the authlogic_openid_selector_example app. When i register, the email id is not returned by the openid provider the first time. But if i delete the account and register again, the email id is returned. But this doesn't seem to be happening in the example hosted here: http://big-glow-mama.heroku.com/. How do i fix this problem? Has this got to do with caching? I have hosted my version of the app here: http://pingauthtest.heroku.com/ I guess the author of authlogic_openid_selector_example app (@holden) has forgotten to commit new changes. :) I looked at my development log and the first time the provider doesn't return the openid.ext1.value.ext0 which contains the email id. This is returned the second time only after having deleted the account first. Edit: This is some extra info for debugging: THIS IS WHEN IT REGISTERS: OpenIdAuthentication::Association Load (5.3ms) SELECT * FROM "open_id_authentication_associations" WHERE ("open_id_authentication_associations"."server_url" = E'https://www.google.com/accounts/o8/ud') Generated checkid_setup request to https://www.google.com/accounts/o8/ud with assocication AOQobUde_9BUnQsk91rb_Sf9tguJ-S7Gpkwahc-nvDGDYAC8nphisNqu Redirected to https://www.google.com/accounts/o8/ud? openid.assoc_handle=AOQobUde_9BUnQsk91rb_Sf9tguJ-S7Gpkwahc-nvDGDYAC8nphisNqu &openid.ax.mode=fetch_request &openid.ax.required=ext0 &openid.ax.type.ext0=http%3A%2F%2Faxschema.org%2Fcontact%2Femail &openid.claimed_id=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0%2Fidentifier_select &openid.identity=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0%2Fidentifier_select &openid.mode=checkid_setup &openid.ns=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0 &openid.ns.ax=http%3A%2F%2Fopenid.net%2Fsrv%2Fax%2F1.0 &openid.ns.sreg=http%3A%2F%2Fopenid.net%2Fextensions%2Fsreg%2F1.1 &openid.realm=http%3A%2F%2Flocalhost%3A3000%2F &openid.return_to=http%3A%2F%2Flocalhost%3A3000%2Faccount%3Ffor_model%3D1%26_method%3Dpost%26open_id_complete%3D1 &openid.sreg.required=email Completed in 3574ms (DB: 14) | 302 Found [http://localhost/account] THIS IS WHEN IT USES SESSIONS: OpenIdAuthentication::Association Load (5.3ms) SELECT * FROM "open_id_authentication_associations" WHERE ("open_id_authentication_associations"."server_url" = E'https://www.google.com/accounts/o8/ud') Generated checkid_setup request to https://www.google.com/accounts/o8/ud with assocication AOQobUde_9BUnQsk91rb_Sf9tguJ-S7Gpkwahc-nvDGDYAC8nphisNqu Redirected to https://www.google.com/accounts/o8/ud? openid.assoc_handle=AOQobUde_9BUnQsk91rb_Sf9tguJ-S7Gpkwahc-nvDGDYAC8nphisNqu &openid.ax.mode=fetch_request &openid.claimed_id=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0%2Fidentifier_select &openid.identity=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0%2Fidentifier_select &openid.mode=checkid_setup &openid.ns=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0 &openid.ns.ax=http%3A%2F%2Fopenid.net%2Fsrv%2Fax%2F1.0 &openid.ns.sreg=http%3A%2F%2Fopenid.net%2Fextensions%2Fsreg%2F1.1 &openid.realm=http%3A%2F%2Flocalhost%3A3000%2F &openid.return_to=http%3A%2F%2Flocalhost%3A3000%2Fuser_session%3Ffor_session%3D1%26_method%3Dpost%26open_id_complete%3D1 Completed in 2708ms (DB: 15) | 302 Found [http://localhost/user_session]

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  • GDL Presents: Creative Sandbox | DoubleClick Rich Media

    GDL Presents: Creative Sandbox | DoubleClick Rich Media Tune in to hear about three cool, new campaigns that use DoubleClick Rich Media, from the core creative teams at clickTag, Spinnaker and Grow Interactive in conversation with a DoubleClick Rich Media expert. They'll talk about how they pushed the possibilities of the DoubleClick Rich Media platform - and will inspire you to do the same. From: GoogleDevelopers Views: 0 0 ratings Time: 01:00:00 More in Science & Technology

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  • Twazzup and App Engine

    Twazzup and App Engine An interview with the developers behind twazzup.com on how App Engine helps them run their application. From: GoogleDevelopers Views: 1298 7 ratings Time: 08:37 More in Science & Technology

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  • What's the most accurate way to determine user geolocation in the browser?

    - by Crashalot
    I found a few examples suggesting Google AJAX APIs. This link typifies the advice I have found so far: http://briancray.com/2009/05/29/find-web-visitors-location-javascript-google-api/ However, the location is often wrong with the Google APIs. Other sites seem to know exactly which city I'm in, though, without me entering any information. Suggestions? Is there something cross-browser (ignoring IE6) and reliable?

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  • MySQL table export to HTML

    - by countnazgul
    Hi all, I've got a little problem with exporting MySQL data to html. The problem is that in one field i have values like this: <a href="http://google.com">Google</a> and when i export the table in html format the generated html table for this fields contains: &lt;a href=&quot;http://google.com&quot;&gt;Google&lt;/a&gt; which is not a valid html link. Is there way to export the table without mysql to convert the < and > chars? Thanks!

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  • Advanced Java book in the lines of CLR via c# or C# in Depth?

    - by devoured elysium
    I want to learn about how things work in depth in Java. Coming from a c# background, there were a couple of very good books that go really deep in c# (C# in depth, CLR via c#, just to name the most popular). Is there anything like that in Java? I searched it up on amazon but nothing seemed to go that deep in Java as the two above go in c#. I don't want to know more about specific classes, or how to use this library or that other library, I want to learn how the objects are created on memory, how they get created on the stack, heap, etc. A more fundamental knowledge, let's say. I've read some chapters of Effective Java and The Java Programming Language but they don't seem to go so deep as I'd want them to go. Maybe there are other people that know both c# and Java that have read any of the referred books and know any that might be useful? Thanks

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  • Happy Birthday

    Today marks a special day for us on the App Engine team. It was just thirty-six years ago today that IBM announced the IBM System/360 . As Wikipedia...

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  • GDL Presents: Women Techmakers with SoftTech VC and NewME Accelerator

    GDL Presents: Women Techmakers with SoftTech VC and NewME Accelerator Stephanie Palmeri of SoftTech VC and Angela Benton of NewMe Accelerator engage with Mary Grove and Stephanie Liu on diversity in the investment space, expounding on their personal experiences growing into skills that have enabled them to excel in this realm. Hosts: Mary Grove - Head of Global Entrepreneurial Outreach | Stephanie Liu - Senior Program Manager, Developer Relations Guests: Stephanie Palmeri - Principal with SoftTech VC | Angela Benton - Founder & CEO NewME Accelerator From: GoogleDevelopers Views: 0 0 ratings Time: 01:00:00 More in Science & Technology

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  • Breaking through the class sealing

    - by Jason Crease
    Do you understand 'sealing' in C#?  Somewhat?  Anyway, here's the lowdown. I've done this article from a C# perspective, but I've occasionally referenced .NET when appropriate. What is sealing a class? By sealing a class in C#, you ensure that you ensure that no class can be derived from that class.  You do this by simply adding the word 'sealed' to a class definition: public sealed class Dog {} Now writing something like " public sealed class Hamster: Dog {} " you'll get a compile error like this: 'Hamster: cannot derive from sealed type 'Dog' If you look in an IL disassembler, you'll see a definition like this: .class public auto ansi sealed beforefieldinit Dog extends [mscorlib]System.Object Note the addition of the word 'sealed'. What about sealing methods? You can also seal overriding methods.  By adding the word 'sealed', you ensure that the method cannot be overridden in a derived class.  Consider the following code: public class Dog : Mammal { public sealed override void Go() { } } public class Mammal { public virtual void Go() { } } In this code, the method 'Go' in Dog is sealed.  It cannot be overridden in a subclass.  Writing this would cause a compile error: public class Dachshund : Dog { public override void Go() { } } However, we can 'new' a method with the same name.  This is essentially a new method; distinct from the 'Go' in the subclass: public class Terrier : Dog { public new void Go() { } } Sealing properties? You can also seal seal properties.  You add 'sealed' to the property definition, like so: public sealed override string Name {     get { return m_Name; }     set { m_Name = value; } } In C#, you can only seal a property, not the underlying setters/getters.  This is because C# offers no override syntax for setters or getters.  However, in underlying IL you seal the setter and getter methods individually - a property is just metadata. Why bother sealing? There are a few traditional reasons to seal: Invariance. Other people may want to derive from your class, even though your implementation may make successful derivation near-impossible.  There may be twisted, hacky logic that could never be second-guessed by another developer.  By sealing your class, you're protecting them from wasting their time.  The CLR team has sealed most of the framework classes, and I assume they did this for this reason. Security.  By deriving from your type, an attacker may gain access to functionality that enables him to hack your system.  I consider this a very weak security precaution. Speed.  If a class is sealed, then .NET doesn't need to consult the virtual-function-call table to find the actual type, since it knows that no derived type can exist.  Therefore, it could emit a 'call' instead of 'callvirt' or at least optimise the machine code, thus producing a performance benefit.  But I've done trials, and have been unable to demonstrate this If you have an example, please share! All in all, I'm not convinced that sealing is interesting or important.  Anyway, moving-on... What is automatically sealed? Value types and structs.  If they were not always sealed, all sorts of things would go wrong.  For instance, structs are laid-out inline within a class.  But what if you assigned a substruct to a struct field of that class?  There may be too many fields to fit. Static classes.  Static classes exist in C# but not .NET.  The C# compiler compiles a static class into an 'abstract sealed' class.  So static classes are already sealed in C#. Enumerations.  The CLR does not track the types of enumerations - it treats them as simple value types.  Hence, polymorphism would not work. What cannot be sealed? Interfaces.  Interfaces exist to be implemented, so sealing to prevent implementation is dumb.  But what if you could prevent interfaces from being extended (i.e. ban declarations like "public interface IMyInterface : ISealedInterface")?  There is no good reason to seal an interface like this.  Sealing finalizes behaviour, but interfaces have no intrinsic behaviour to finalize Abstract classes.  In IL you can create an abstract sealed class.  But C# syntax for this already exists - declaring a class as a 'static', so it forces you to declare it as such. Non-override methods.  If a method isn't declared as override it cannot be overridden, so sealing would make no difference.  Note this is stated from a C# perspective - the words are opposite in IL.  In IL, you have four choices in total: no declaration (which actually seals the method), 'virtual' (called 'override' in C#), 'sealed virtual' ('sealed override' in C#) and 'newslot virtual' ('new virtual' or 'virtual' in C#, depending on whether the method already exists in a base class). Methods that implement interface methods.  Methods that implement an interface method must be virtual, so cannot be sealed. Fields.  A field cannot be overridden, only hidden (using the 'new' keyword in C#), so sealing would make no sense.

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