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  • "Invalid assignment" error from == operator

    - by Tom
    I was trying to write a simple method: boolean validate(MyObject o) { // propertyA && propertyB are not primitive types. return o.getPropertyA() == null && o.getPropertyB() == null; } And got a strange error on the == null part: Syntax error on token ==. Invalid assignment operator. Maybe my Java is rusty after a season in PLSQL. So I tried a simpler example: Integer i = 4; i == null; // compile error: Syntax error on token ==. Invalid assignment operator. Integer i2 = 4; if (i == null); //No problem How can this be? I'm using jdk160_05. To clarify: I'm not trying to assign anything, just do an && operation between two boolean values. I don't want to do this: if (o.propertyA() == null && o.propertyB() == null) { return true; } else { return false; }

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  • Using Threads to Handle Sockets

    - by user340468
    I am working on a java program that is essentially a chat room. This is an assignment for class so no code please, I am just having some issues determining the most feasible way to handle what I need to do. I have a server program already setup for a single client using threads to get the data input stream and a thread to handle sending on the data output stream. What I need to do now is create a new thread for each incoming request. My thought is to create a linked list to contain either the client sockets, or possibly the thread. Where I am stumbling is figuring out how to handle sending the messages out to all the clients. If I have a thread for each incoming message how can I then turn around and send that out to each client socket. I'm thinking that if I had a linkedlist of the clientsockets I could then traverse the list and send it out to each one, but then I would have to create a dataoutputstream each time. Could I create a linkedlist of dataoutputstreams? Sorry if it sounds like I'm rambling but I don't want to just start coding this, it could get messy without a good plan. Thanks!

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  • Very simple code for number search gives me infinite loop

    - by Joshua
    Hello, I am a newbie Computer Science high school student and I have trouble with a small snippet of code. Basically, my code should perform a basic CLI search in an array of integers. However, what happens is I get what appears to be an infinite loop (BlueJ, the compiler I'm using, gets stuck and I have to reset the machine). I have set break points but I still don't quite get the problem...(I don't even understand most of the things that it tells me) Here's the offending code (assume that "ArrayUtil" works, because it does): import java.util.Scanner; public class intSearch { public static void main(String[] args) { search(); } public static void search() { int[] randomArray = ArrayUtil.randomIntArray(20, 100); Scanner searchInput = new Scanner(System.in); int searchInt = searchInput.nextInt(); if (findNumber(randomArray, searchInt) == -1) { System.out.println("Error"); }else System.out.println("Searched Number: " + findNumber(randomArray, searchInt)); } private static int findNumber(int[] searchedArray, int searchTerm) { for (int i = 0; searchedArray[i] == searchTerm && i < searchedArray.length; i++) { return i; } return -1; } } This has been bugging me for some time now...please help me identify the problem!

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  • How to send XML data through socket InputStream

    - by THeK3nger
    Hi, I'm trying to write a client-server application in Java with an XML-based protocol. But I have a great problem! See this part of client code: InputStream incoming = skt.getInputStream(); //I get Stream from Socket. OutputStream out = skt.getOutputStream(); [...] XMLSerializer serializer = new XMLSerializer(); //This create an XML document. tosend = WUTPClientWriter.createMessage100(projectid, cpuclock, cpunumber); serializer.setOutputByteStream(out); serializer.serialize(tosend); At this point server fall in deadlock. It wait for EOF but I can't send it because if I use out.close(); or skt.shutdownOutput(); I close Socket and I must keep alive this connection. I can't send '\0' becouse I get Parse Error in the server. How can I do? Can I "close" output stream without close socket? RESOLVED I've created new class XMLStreamOutput and XMLStreamInput with advanced Stream gesture.

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  • Calculating percent "x/y * 100" always results in 0?

    - by Patrick Beninga
    In my assignment i have to make a simple version of Craps, for some reason the percentage assignments always produce 0 even when both variables are non 0, here is the code. import java.util.Random; Header, note the variables public class Craps { private int die1, die2,myRoll ,myBet,point,myWins,myLosses; private double winPercent,lossPercent; private Random r = new Random(); Just rolls two dies and produces their some. public int roll(){ die1 = r.nextInt(6)+1; die2 = r.nextInt(6)+1; return(die1 + die2); } The Play method, this just loops through the game. public void play(){ myRoll = roll(); point = 0; if(myRoll == 2 ||myRoll == 3 || myRoll == 12){ System.out.println("You lose!"); myLosses++; }else if(myRoll == 7 || myRoll == 11){ System.out.println("You win!"); myWins++; }else{ point = myRoll; do { myRoll = roll(); }while(myRoll != 7 && myRoll != point); if(myRoll == point){ System.out.println("You win!"); myWins++; }else{ System.out.println("You lose!"); myLosses++; } } } This is where the bug is, this is the tester method. public void tester(int howMany){ int i = 0; while(i < howMany){ play(); i++; } bug is right here in these assignments statements winPercent = myWins/i * 100; lossPercent = myLosses/i* 100; System.out.println("program ran "+i+" times "+winPercent+"% wins "+ lossPercent+"% losses with "+myWins+" wins and "+myLosses+" losses"); } }

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  • Printing the "source" class in a log statement with a log4j wrapper

    - by Dur4ndal
    My application has a homebrew logging class that I'm migrating to using log4j under the covers. However, since I'm using the homebrew class to pass the rest of the application's logging statements to log4j, the output statements are logged as coming from the wrapper class instead of the source class. Is there a way to ensure that the "correct" source is being shown besides creating new org.apache.log4j.Logger instances for every log statement? I've also tried using the Logger.log(String callerFQCN, Priority level, Object message, Throwable t) method, but it doesnt seem to be working, for example: public class Logger2 { public static org.apache.log4j.Logger log4JLogger = org.apache.log4j.Logger.getLogger(Logger2.class); public static void warning(Object source, String message) { log(source, message, Level.WARN, null) } private static void log(Object source, String message, Level level, Throwable t) { String className = source.getClass().getName(); System.out.println("Logging class should be " + className); log4JLogger.log(className, loggingLevel, message, t); } } When called by: public void testWarning() { Logger2.warning(new Integer(3), "This should warn"); } Prints: Logging class should be java.lang.Integer 2010-05-25 10:49:57,152 WARN test.Logger2 - This should warn

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  • How to get a specific attribute from an object list?

    - by anarhikos
    I've an array keeping a list of Group objects. I want to set this list to the DropDownChoice component. However I want to show the end user only the name attribute of Group objects, and then get the selected values' id attribute to add database. What to do? private List<Group> groupTypes; DatabaseApp db = new DatabaseApp(); groupTypes = db.getGroups(); groupDropDownChoice = new DropDownChoice("type", groupTypes); ... ... addUserForm.add(new Button("submit"){ @Override public void onSubmit(){ Group group = (Group) groupDropDownChoice.getModelObject(); ... ... db.addUser(group.getId(), den, name, login, email, password1); DatabaseApp.java public List<Group> getGroups() throws SQLException{ List<Group> groups = new ArrayList<Group>(); try { String query = "SELECT * FROM [GROUP]"; Statement statement = db.createStatement(); ResultSet result = statement.executeQuery(query); while(result.next()){ int id = result.getInt("ID"); String name = result.getString("NAME"); groups.add(new Group(id, name)); } result.close(); } catch (SQLException ex) { throw new SQLException(ex.getMessage()); } return groups; }

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  • Ant Junit tests are running much slower via ant than via IDE - what to look at?

    - by Alex B
    I am running my junit tests via ant and they are running substantially slower than via the IDE. My ant call is: <junit fork="yes" forkmode="once" printsummary="off"> <classpath refid="test.classpath"/> <formatter type="brief" usefile="false"/> <batchtest todir="${test.results.dir}/xml"> <formatter type="xml"/> <fileset dir="src" includes="**/*Test.java" /> </batchtest> </junit> The same test that runs in near instantaneously in my IDE (0.067s) takes 4.632s when run through Ant. In the past, I've been able to speed up test problems like this by using the junit fork parameter but this doesn't seem to be helping in this case. What properties or parameters can I look at to speed up these tests? More info: I am using the reported time from the IDE vs. the time that the junit task outputs. This is not the sum total time reported at the end of the ant run. So, bizarrely, this problem has resolved itself. What could have caused this problem? The system runs on a local disk so that is not the problem.

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  • Eclipse Ant Builder problem

    - by styx777
    I made a custom ant script to automatically create a jar file each time I do a build. This is how it looks like: <?xml version="1.0" encoding="UTF-8"?> <project name="TestProj" basedir="." default="jar"> <property name="dist" value="dist" /> <property name="build" value="bin/test/testproj" /> <target name="jar"> <jar destfile="${dist}/TestProj.jar"> <manifest> <attribute name="Main-Class" value="test.testproj.TestProj" /> </manifest> <fileset dir="${build}" /> </jar> </target> </project> I added it by Right clicking my project properties builders clicked new Ant builder then I specified the location of the above xml file. However, when I run it by doing: java -jar TestProj.jar I get a NoClassDefFoundError test/testproj/TestProj I'm using Eclipse in Ubuntu. TestProj is the name of the class and it's in package test.testproj I'm pretty sure there's something wrong with the manifest and probably the location of the xml file as well but I'm not sure how to fix this. Any ideas?

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  • Google App Engine/GWT/Eclipse Plugin Newbie Question- how to autobuild client side resources?

    - by Dieter Hanover
    Hi there, I'm tinkering with the default GWT application generated by the Google Eclipse plugin when I click the Google "New Web Application Project" button in Eclipse 3.5. This will no doubt be familiar to many of you.. basically there is an h1 title stating "Web Application Starter Project," a text field, and a Send button. What I've found is that whenever I make changes to the client side resources, e.g. change the text on the Send button to "Submit" in the .java file, Eclipse does not appear to autobuild these resources. In fact I have to rebuild the entire project in order for these changes to be reflected in my browser. I do have "build automatically" selected in eclipse. I should state that this is my second GWT project, the first was almost entirely server side (restlet on GAE) and everything built automatically nicely. When I first tried this new project with updated client resources, on refreshing my browser, the browser stated "you may need to (re)compile your project." I'm not sure if this is relevant but I thought I'd mention it all the same. So what's going on? How do I get Eclipse/GWT to autobuild these client side resources? Cheers for any help you can offer! :-)

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  • Recommendation for using equals in Entities and avoiding LazyInitializationExceptions?

    - by huxendupsel
    In the beginning there is a problem that wants to be solved. In my case i got an LazyInitializationException while using indexof in a Collection to retrieve an Object for manipulation. Here i start to think about using equals in EntityBeans (OR-Mapper at all). I know there are some discussions about overriding equals in association with OR-Mapper as hibernate like [1] Entities equals(), hashCode() and toString(). How to correctly implement them? [2] To equals and hashcode or not on entity classes, that is the question. [3] Overriding equals and hashCode in Java I currently have some entities which implements the equals but inside the code i could not use equals several times because of the LazyInitializationExceptions. So i had to workaround and use eg. the name property of the object to identify it's equality. From my point of view the whole 'LazyInitializationException-thing' is not really mentioned in this questions. I'd like to know have you got some good patterns or real live recommendations how to avoid such exception in an equal-Method. Shall i use some helper Methodes to distinguish if a Object of a class is already initialized (4) or should i apdicate the use of equals and use helper classes instead (2)? And what is about catching LazyInitializationExceptions in the equals? [Edit]: If you put equals in context with the initialization of the Object then it will gain importance. Sometimes it is nessesary to have the Object fully initialized but sometimes you don't want to. Because you just need the Object itself (name, id, ...) not its Collection-Properties. So just for equalization you have to reattach the Object and load the whole bunch you don't realy need? Are there any other solutions for such a problem?

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  • New to J2EE; architecture suggestions for a service/daemon?

    - by Kate
    I am brand new to the J2EE world. As an exercise to try and familiarize myself with J2EE, I'm trying to create a tiered web-app, but I'm getting a little stuck on what the best way is to spin up a service in the background that does work. Paramters of the service: It must open and hold a socket connection and receive information from the connected server. There is a 1-to-1 correlation between a user and a new socket connection. So the idea is the user presses a button on the web-page, and somewhere on the server a socket connection is opened. For the remainder of the users session (or until the user presses some sort of disconnect button) the socket remains open and pushes received information to some sort of centralized store that servlets can query and return to the user via AJAX. Is there a J2EE type way to handle this situation? Naturally what I would think to do is to just write a Java application that listens on a port that the servlets can connect to and spawns new threads that open these sockets, but that seems very ad-hoc to me. (PS: I am also new to Stack Overflow, so forgive me if it takes me some time to figure the site out!)

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  • add two float values in java

    - by user1845286
    acually i try to add two float values in java like this import java.text.DecimalFormat; class ExactDecimalValue { final strictfp static public void main(String... arg) { float f1=123.00000f; float f2=124.00000f; float f3=f1+f2; System.out.println(f1+f2); System.out.println("sum of two floats:"+f3); /*my expected output is:247.00000 but comming output is:247.0 and 247*/ } } Now what i can do to get the value in this format:247.00000. please any one help me. Thanks & Regards venkatesh

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  • Why can't I pass an object of type T to a method on an object of type <? extends T>?

    - by Matt
    In Java, assume I have the following class Container that contains a list of class Items: public class Container<T> { private List<Item<? extends T>> items; private T value; public Container(T value) { this.value = value; } public void addItem(Item item) { items.add(item); } public void doActions() { for (Item item : items) { item.doAction(value); } } } public abstract class Item<T> { public abstract void doAction(T item); } Eclipse gives the error: The method doAction(capture#1-of ? extends T) in the type Item is not applicable for the arguments (T) I've been reading generics examples and various postings around, but I still can't figure out why this isn't allowed. Eclipse also doesn't give any helpful tips in its proposed fix, either. The variable value is of type T, why wouldn't it be applicable for ? extends T?.

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  • Java api to exiftool

    - by mujer-esponja
    Hi! I am interesting en parser the exiftool result with a java api or something like that. I have been researching, but i didn't find any example. For example, how could I get theese results in my java project?? ExifTool Version Number : 8.22 File Name : ExifTool.jpg Directory : t/images File Size : 24 kB File Modification Date/Time Etc.. I am looking forwar a 'how to' or something like that. Thanks in advance!

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  • Strange Puzzle - Invalid memory access of location

    - by Rob Graeber
    The error message I'm getting consistently is: Invalid memory access of location 0x8 rip=0x10cf4ab28 What I'm doing is making a basic stock backtesting system, that is iterating huge arrays of stocks/historical data across various algorithms, using java + eclipse on the latest Mac Os X. I tracked down the code that seems to be causing it. A method that is used to get the massive arrays of data and is called thousands of times. Nothing is retained so I don't think there is a memory leak. However there seems to be a set limit of around 7000 times I can iterate over it before I get the memory error. The weird thing is that it works perfectly in debug mode. Does anyone know what debug mode does differently in Eclipse? Giving the jvm more memory doesn't help, and it appears to work fine using -xint. And again it works perfectly in debug mode. public static List<Stock> getStockArray(ExchangeType e){ List<Stock> stockArray = new ArrayList<Stock>(); if(e == ExchangeType.ALL){ stockArray.addAll(getStockArray(ExchangeType.NYSE)); stockArray.addAll(getStockArray(ExchangeType.NASDAQ)); }else if(e == ExchangeType.ETF){ stockArray.addAll(etfStockArray); }else if(e == ExchangeType.NYSE){ stockArray.addAll(nyseStockArray); }else if(e == ExchangeType.NASDAQ){ stockArray.addAll(nasdaqStockArray); } return stockArray; } A simple loop like this, iterated over 1000s of times, will cause the memory error. But not in debug mode. for (Stock stock : StockDatabase.getStockArray(ExchangeType.ETF)) { System.out.println(stock.symbol); }

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  • Which one gives you more advantages: Microsoft or SUN/Oracle certification?

    - by edwin.nathaniel
    Which one gives you more advantages: Microsoft or SUN/Oracle certification? If you don't mind, please relate your answer to your career (dev, sys-admin, dba), industry (finance, general consulting, business apps, software house), and location (where you live, does it influence your decision?) as well. One reason I asked this because I heard that having MCP (in C#, MCSAD or whatever the cert is called these days) could give you extra point from the employer perspective if they're a Microsoft Partner. I don't quite understand why and am also wondering if SUN/Oracle certificate holder have similar edge/benefit. I'm also interested to know if Certification plays role where you live. For example: certification could be a big negative sign in Silicon Valley, but might be helpful if you're in other US/Canada cities or outside USA/Canada. If you are an independent software consultant, do these certification helps you win bids? I totally understand that this question might be subjective and could be "closed". But it doesn't hurt to ask I suppose. I also understand that there are people who dislike/disagree (or have negative perspective on technology certification). While there are people who have the opinion that "these are not the kind of employers you would want to work with", I respect you guys, but sometime a pure software product company might not exist in certain cities in the world. And if certification can help one's career somewhere else, I guess that means more opportunities right? I've had experienced in both platforms: (short) .NET and (not too long) Java (minus Oracle DB stuff), but I think it's about time I have to pick one of them and be good at. Where I live right now might also dictates my career albeit insignificant. Anyhow, this last paragraph is just tiny blurb. Thanks!

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  • math.Random isn't working right

    - by RandomlyKnighted
    I'm trying to simulate a coin flip using the code below. public class Coin { public static double result; int[] count = new count[2]; public static void flip() { result = Math.random(); } public static boolean isHeads() { if (result == 0.0) { count[0]++; return false; } else { count[1]++; return true; } } public static void main(String[] args) { flip(); isHeads(); System.out.println(count[0]); System.out.println(count[1]); } } For some reason Eclipse says that the import java.util.Random; is never used even though I'm clearly using it. I didn't put my for loop into the code above but it loops n number of times and then outputs the result. No matter how many times it loops it always returns that the result is greater than 0.0 which can't be right. Am I calling Math.random incorrectly?

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  • JAR file: Could not find main class

    - by ApertureT3CH
    Okay, I have a strange problem. I wanted to run one of my programs as a .jar file, but when I open it by double-clicking it, I get an error message like "Could not find main class, program is shutting down". I'm pretty sure I did everything right, the jar should work afaik. I also tried other programs, it's the same with every single one. (I'm creating the .jar's through BlueJ) There is no problem when I run them through a .bat . And here comes the strangest thing of all: The .jar's have worked some time ago (one or two months I guess), and I don't remember doing anything different. It's the same BlueJ-Version. Okay, maybe Java updated and something got messed up... I googled, but I couldn't find a solution. (some people seem to have a similar problem, and it seems to be only them who can't run their .jar's; they uploaded them and other people say the .jar's run fine.) What could be the problem? How can I solve it? I'd really appreciate some help here. Thank you :) ApertureT3CH EDIT: okay guys, you're making me unsure here. Imma check the manifest again, at this unholy time ( 1:34 am ) :P EDIT2: This is my MANIFEST.MF Manifest-Version: 1.0 Class-Path: Main-Class: LocalChatClientGUI [empty line] [empty line] The Main class is correct. EDIT3: Thanks to hgrey: There is nothing wrong with the jar. I can run it from a bat file, which actually should not be different from double-clicking the jar, right? Yet I get the error when clicking it, and it works fine through the bat. EDIT4: I finally solved the problem. I re-installed the JRE and now it works, although I can't see any version differences. Thanks to everyone!

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  • Peculiar JRE behaviour running RMI server under load, should I worry?

    - by darri
    I've been developing a minimalistic Java rich client CRUD application framework for the past few years, mostly as a hobby but also actively using it to write applications for my current employer. The framework provides database access to clients either via a local JDBC based connection or a lightweight RMI server. Last night I started a load testing application, which ran 100 headless clients, bombarding the server with requests, each client waiting only 1 - 2 seconds between running simple use cases, consisting of selecting records along with associated detail records from a simple e-store database (Chinook). This morning when I looked at the telemetry results from the server profiling session I noticed something which to me seemed strange (and made me keep the setup running for the remainder of the day), I don't really know what conclusions to draw from it. Here are the results: Memory GC activity Threads CPU load Interesting, right? So the question is, is this normal or erratic? Is this simply the JRE (1.6.0_03 on Windows XP) doing it's thing (perhaps related to the JRE configuration) or is my framework design somehow causing this? Running the server against MySQL as opposed to an embedded H2 database does not affect the pattern. I am leaving out the details of my server design, but I'll be happy to elaborate if this behaviour is deemed erratic.

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  • Is the situation with Java ME improving?

    - by mike g
    It seems to be the consensus that developing for Java ME is not as cross platform as you might expect, particularly compared to say java SE, but it is difficult to assess how the situation is evolving. Is the situation improving significantly? Are problematic implementations being patched? Are problematic implementations dying out as a proportion of mobile devices? Is the tool chain improving? Are there ways to identify at least some cross platform 'errors' without necessarily deploying to each and every device?

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  • How to get the parameter names of an object's constructors (reflection)?

    - by Tom
    Say I somehow got an object reference from an other class: Object myObj = anObject; Now I can get the class of this object: Class objClass = myObj.getClass(); Now, I can get all constructors of this class: Constructor[] constructors = objClass.getConstructors(); Now, I can loop every constructor: if (constructors.length > 0) { for (int i = 0; i < constructors.length; i++) { System.out.println(constructors[i]); } } This is already giving me a good summary of the constructor, for example a constructor public Test(String paramName) is shown as public Test(java.lang.String) Instead of giving me the class type however, I want to get the name of the parameter.. in this case "paramName". How would I do that? I tried the following without success: if (constructors.length > 0) { for (int iCon = 0; iCon < constructors.length; iCon++) { Class[] params = constructors[iCon].getParameterTypes(); if (params.length > 0) { for (int iPar = 0; iPar < params.length; iPar++) { Field fields[] = params[iPar].getDeclaredFields(); for (int iFields = 0; iFields < fields.length; iFields++) { String fieldName = fields[i].getName(); System.out.println(fieldName); } } } } } Unfortunately, this is not giving me the expected result. Could anyone tell me how I should do this or what I am doing wrong? Thanks!

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  • Fast compiler error messages in Eclipse

    - by Chris Conway
    As a new Eclipse user, I am constantly annoyed by how long it takes compiler error messages to display. This is mostly only a problem for long errors that don't fit in the status bar or the "Problems" tab. But I get enough long errors in Java—especially with generics—that this is a nagging issue. (Note: The correct answer to this question is not "get better at using generics." ;-) The ways I have found to display an error are: Press Ctrl+. or execute the command "Next Annotation". The next error is highlighted and its associated message appears in the status bar (if it is short enough). The error is also highlighted in the "Problems" tab, if it is open, but the tab is not automatically brought to the top. Hover the mouse over the error. After a noticeable lag, the error message appears as a "tool tip", along with any associated "Quick Fixes." Hover the mouse over the error icon on the left side of the editing pane. After a noticeable lag, all of the error messages for that line appear as a "tool tip." Clicking on the icon brings up "Quick Fixes." What I would like is for Ctrl+. to automatically and instantly bring up the complete error message (I don't care where). Is this a configurable option? [UPDATE] @asterite's "Ctrl+. F2" is almost it. How do I make "Next Annotation, then Show Tooltip Description" a macro bound to a single keystroke?

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  • InputStreamBody in HttpMime 4.0.3 settings for content-length

    - by Ram
    I am trying to send a multi part formdata post through my java code. Can someone tell me how to set Content Length in the following?? There seem to be headers involved when we use InputStreamBody which implements the ContentDescriptor interface. Doing a getContentLength on the InputStreamBody gives me -1 after i add the content. I subclassed it to give contentLength the length of my byte array but am not sure if other headers required by ContentDescriptor will be set for a proper POST. HttpClient httpclient = new DefaultHttpClient(); HttpPost httpPost = new HttpPost(myURL); ContentBody cb = new InputStreamBody(new ByteArrayInputStream(bytearray), myMimeType, filename); //ContentBody cb = new ByteArrayBody(bytearray, myMimeType, filename); MultipartEntity mpentity = new MultipartEntity(HttpMultipartMode.BROWSER_COMPATIBLE); mpentity.addPart("key", new StringBody("SOME_KEY")); mpentity.addPart("output", new StringBody("SOME_NAME")); mpentity.addPart("content", cb); httpPost.setEntity(mpentity); HttpResponse response = httpclient.execute(httpPost); HttpEntity resEntity = response.getEntity();

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