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  • How to write custom data to the TCP packet header options field with Java?

    - by snarkov
    As it is defined (see: http://www.freesoft.org/CIE/Course/Section4/8.htm) the TCP header has an 'Options' field. There are a couple of options already defined (see: www.iana.org/assignments/tcp-parameters/) but I want to come up with my very own. (For experimenting/research.) How can I get Java to write (and then read) some custom data to the options field? Bonus question: if it cannot be done with Java. what kind of application can do this? (No, I don't really feel like messing with some kernel-level TCP/IP stack implementation, I want to keep it app level.) Thanks!

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  • For what purpose does java have a float primitive type?

    - by Roman
    I heard plenty times different claims about float type in java. The most popular issues typicaly regard to converting float value to double and vice versa. I read (rather long time ago and not sure that it's actual now with new JVM) that float gives much worse performance then double. And it's also not recommended to use float in scientific applications which should have certain accuracy. I also remember that when I worked with AWT and Swing I had some problems with using float or double (like using Point2D.Float or Point2D.Double). So, I see only 2 advantages of float over double: it needs only 4 bytes while double needs 8 bytes JMM garantees that assignment operation is atomic with float variables while it's not atomic with double's. Are there any other cases where float is better then double? Do you use float's in your applications? It seems to me that the only valuable reason java has float is backward compatibility.

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  • How do I run JUnit tests from inside my java application?

    - by corgrath
    Is it possible to run JUnit tests from inside my java application? Are there test frameworks I can use (such as JUnit.jar?), or am I force to find the test files, invoke the methods and track the exceptions myself? The reason why I am asking is my application requires a lot of work to start launch (lots of dependencies and configurations, etc) and using an external testing tool (like JUnit Ant task) would require a lot of work to set up. It is easier to start the application and then inside the application run my tests. Is there an easy test framework that runs tests and output results from inside a java application or am I forced to write my own framework?

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  • Can a signed Java Applet/Web Start manipulate content in a cross-site IFRAME?

    - by etoleb
    Is it possible for a signed Java Applet or Web Start app to write to the DOM of an IFRAME under a different domain? Does the fact that they're a signed applet/javaws allow them to ignore browsers' standard cross-browser security? If this does work, how well is it supported across the major browsers? Thanks! EDIT: My motivation is to add a browser plugin-like tool to third-party websites I don't control. It's not required that I use Java at all---any ideas or suggestions are encouraged.

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  • File Explorer using Java - how to go about it?

    - by user299988
    Hi, I am set to create a file explorer using Java. The aim is to emulate the behavior of the default explorer as closely as possible, whatever may be the underlying OS. I have done NO GUI programming in Java. I have looked-up Swing, SWT and JFace, and I am beginning my project with this tutorial: http://www.ibm.com/developerworks/opensource/library/os-ecgui1/ I would like to know your opinions about the best approach to tackle this problem. If you could comment on complexity of coding, portability and OS-independence, and efficiency, it would be great. Is there anything else I should know? Do some other ways exist? Thanks a lot!

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  • How can I use my multiple cored dedicated server to run my java application?

    - by Delta
    I have a game built in a java environment and I use JVM. I have 4 cores @ 2.4Ghz and my server is only using one of those cores... I've tried and searched and I still have no guides to setup multiple cores to run the game like, say 1 core for running the character saving + loading, and 1 core for the server itself, and 1 core for a helper to help other cores that need more power. I don't even know if this is possible but this is all in java the operating machine is windows server 2003 and I've tried so hard I just don't know what to do. May someone please help me! Thank you so much!

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  • [java] how to use XML sent by html form?

    - by user32167
    i have html form with textarea in which i paste some XML, for example: <network ip_addr="10.0.0.0/8" save_ip="true"> <subnet interf_used="200" name="lan1" /> <subnet interf_used="254" name="lan2" /> </network> When user submit form, that data is send to Java server, so in headers i get something like that: GET /?we=%3Cnetwork+ip_addr%3D%2210.0.0.0%2F8%22+save_ip%3D%22true%22%3E%0D%0A%3Csubnet+interf_used%3D%22200%22+name%3D%22lan1%22+%2F%3E%0D%0A%3Csubnet+interf_used%3D%22254%22+name%3D%22lan2%22+%2F%3E%0D%0A%3C%2Fnetwork%3E HTTP/1.1 how can i use that in my Java applications? I need to make some calculations on that data and re-send new generated XML.

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  • Append to a file in Java. Is it a joke?

    - by Roman
    I need to append some data to existing file. I started to browse Internet to find out how to do it. And I found this mini (as they say) application to do that: http://www.devdaily.com/java/edu/qanda/pjqa00009.shtml Well I was already annoyed by the fact how complicated are things in Java (in comparison with Python, for example). But this is too much! I just want to add to a file! It should be one line! Not 50! Or do I get something wrong?

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  • Why's a simple change to rt.jar causing the Java Runtime Environment to crash silently?

    - by Tom
    This is what I'm doing: extract contents of my JRE's rt.jar extract src.zip of my JDK (same version) Now, if I copy Runtime.java from the extracted src folder and compile it using javac.exe without any modifications and then put it in the extracted rt folder to finally put everything back in a jar file using jar.exe, everything works as expected. The JRE runs fine. However, if I make the slightest change to Runtime.java and compile it and put it in rt.jar, the JRE crashes whenever I attempt to start it. This is an example of a slight change that causes the silent crash: /** Don't let anyone else instantiate this class */ private Runtime() { System.out.println("This is a test."); } Instead of: /** Don't let anyone else instantiate this class */ private Runtime() {} Could anyone tell me why this is causing my JRE to crash? Thanks in advance.

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  • Multiple indexes for a Java Collection - most basic solution?

    - by chris_l
    Hi, I'm looking for the most basic solution to create multiple indexes on a Java Collection. Required functionality: When a Value is removed, all index entries associated with that value must be removed. Index lookup must be faster than linear search (at least as fast as a TreeMap). Side conditions: It should ideally work with JavaSE (6.0) alone - no extra libraries, if possible. If necessary, then only small (not something like Lucene), common and well tested libraries. No database! Of course, I could write a class that manages multiple Maps myself. But I'd like to know, if it can be done without - while still getting a simple usage similar to using a single indexed java.util.Map. Thanks, Chris

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  • Java: how to have global values inside a class?

    - by HH
    I want less methods. I want a common global TestClass from which I could use any of its value inside the class. import java.util.*; import java.io.*; public class TestClass { TestClass(String hello){ String hallo = hello; String halloSecond = "Saluto!"; } public static void main(String[] args) { TestClass test = new TestClass("Tjena!"); System.out.println("I want "Tjena!": " + test.hallo); TestClass testSecond = new TestClass("1"); System.out.println("I want Saluto!:" + test.halloSecond); System.out.println("I want Saluto!:" + testSecond.halloSecond); // How can I get glob.vars like the "Saluto!"? } }

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  • Why should I use mock objects (Java)? Do all mocking frameworks serve the same purpose?

    - by Mehmet Yesin
    I'm preparing a presentation and I need to get a better understanding of what mocking is, what is the purpose of using it, what are the common situations that I should use mock objects? I found out that there are a bunch of mocking frameworks out there. Do they all do the same thing or do I use a specific framework for specific testing purpose? What are the differences between these frameworks? Which one would you recommend for testing Java? here are some stuff that I found: 1.MockingToolkitComparisonMatrix which seems biased. 2.What are mock objects in Java? This is a year old. I thought there might be some better answer today. Thank you.

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  • Developing multiple user interfaces for an application

    - by denizkocak
    I want to develop an application which has a graphical user interface that could be developed by using different widget toolkits. For example I want to use Qt, GTK+ or even ncurses as a building block for my user interface for the same application. Moreover users could choose which GUI implementation will be used during the next startup of the application without recompiling it first. I wonder what are possible design strategies and design patterns used in the implementation of this design?

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  • Is it faster to use a complicated boolean to limit a ResultSet at the MySQL end or at the Java end?

    - by javanix
    Lets say I have a really big table filled with lots of data (say, enough not to fit comfortably in memory), and I want to analyze a subset of the rows. Is it generally faster to do: SELECT (column1, column2, ... , columnN) FROM table WHERE (some complicated boolean clause); and then use the ResultSet, or is it faster to do: SELECT (column1, column2, ... , columnN) FROM table; and then iterate over the ResultSet, accepting different rows based on a java version of your boolean condition? I think it comes down to whether the Java iterator/boolean evaluator is faster than the MySQL boolean evaluator.

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  • Is Java serialization a tool to shrink the memory footprint?

    - by Pentius
    Hey folks, does serialization in Java always have to shrink the memory that is used to hold an object structure? Or is it likely that serialization will have higher costs? In other words: Is serialization a tool to shrink the memory footprint of object structures in Java? Edit I'm totally aware of what serialization was intended for, but thanks anyway :-) But you know, tools can be misused. My question is, whether it is a good tool to decrease the memory usage. So what reasons can you imagine, why memory usage should increase/decrease? What will happen in most cases?

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  • Why are interfaces not [Serializable]?

    - by Zac Harlan
    I would think that adding that attribute to an interface would be helpful make sure you do not create classes that use the interface and forget to make them serializable. This could be a very fundamental question, but I wanted to ask the experts.

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