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• Why can I derived from a templated/generic class based on that type in C# / C++

  - by stusmith

  Title probably doesn't make a lot of sense, so I'll start with some code: class Foo : public std::vector<Foo> { }; ... Foo f; f.push_back( Foo() ); Why is this allowed by the compiler? My brain is melting at this stage, so can anyone explain whether there are any reasons you would want to do this? Unfortunately I've just seen a similar pattern in some production C# code and wondered why anyone would use this pattern.

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• Reference to an instance method of a particular object

  - by Andrey

  In the following code, if i try to pass method reference using the class name, works. But passing the reference variable compiler gives an error, i do not understand why? public class User { private String name; public User(String name) { this.name = name; } public void printName() { System.out.println(name); } } public class Main { public static void main(String[] args) { User u1 = new User("AAA"); User u2 = new User("BBB"); User u3 = new User("ZZZ"); List<User> userList = Arrays.asList(u1, u2, u3); userList.forEach(User::printName); // works userList.forEach(u1::printName); // compile error } } Thanks,

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• @Intertceptors does not work for web bean for JSF page.

  - by Drevlyanin

  @Named @ConversationScoped @Interceptors(MyInterceptor.class) public class BeanWeb implements Serializable { public String methodThrowException throws Exception() { throws new Exception(); } } public class MyInterceptor { @AroundInvoke public Object intercept(InvocationContext ic) throws Exception { try { return ic.proceed(); } catch (Exception e) { return null; } } } For @Stateless beans interceptor works, but for the BeanWeb interceptor does not work. And we have never entered into "intercept" method. Why is this happening? How could intercept method calls in BeanWeb? P.S.: All this spin under Glassfish 3.x.

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• php class crash course

  - by rabidmachine9

  Hello people, I'm sorry for this question but I'm getting crazy trying to write my first php clash, it is supposed to connect me to server and to a database but I'm always getting this error: Parse error: syntax error, unexpected ',', expecting T_PAAMAYIM_NEKUDOTAYIM in /Applications/XAMPP/xamppfiles/htdocs/classTest/test.php on line 9 thanks in advance, here is the code: <?php // include 'DBConnect.php'; class DBConnect { function connection($hostname = "localhost", $myname = "root", $pass = ''){ mysql_connect(&hostname, &myname, &pass) or die("Could not connect!"); //Connect to mysql } function choose($dbnam){ mysql_select_db(&dbnam) or die("Couldn't find database!"); //fnd specific db } } $a = new DBConnect(); $connect = $a->connection("localhost", "root"); $a->choose('mydb'); ?>

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• returning values from function or method multiple times by only calling the class once

  - by Sokhrat Sikar

  I have a members.php file that shows my websites members. I echo members name by using foreach method. A method of Members class returns an array, then I use foreach loop in the members.php file to echo the members. I am trying to aovid writing php code in my members.php file. Is there a way to avoid using foreach inside members.php file? For example, is it possible to return value from a method couple of times? (by only calling the object once). Just like how we normally call the functions? This question doesn't make sense, but I am just trying to see if there is a away around this issue?

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• Policies Array Class-Design wrapper

  - by PT

  Hi, i want to write an wrapper for different Array Classes with different Policies. For example: typedef ArrayType<useValArray,StdAllocator> Array; // one global assignment I want to use the class like a blitz++ Array for example: Array<double,2> x(2,2); //maps the Array to an Valarray or to a Blitz++ Array Array<double,2> x2(5,6); is this Posible? Which technics i need to realise that?

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• calling normal java class forom servlet

  - by Mohammed_Q

  Hello Every time im trying to accesses a normal java class from servlet (from other project) it gives me classNotFound exception, any idea how to fix this problem thanks in advance

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• Generic collection class?

  - by Mark

  Is there anyway I can do this? class TSOC<TCollection, TValue> : ICollection<TValue>, INotifyCollectionChanged where TCollection : ICollection { private TCollection<TValue> collection; } It doesn't like my definition of collection. I'd prefer the definition to look like TSOC<TCollection> where the user can pass in List<int> or something, but then I need to pull out the "int" to know what interface to implement.

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• class member access specifiers

  - by pdehaan

  I understand what the typical access specifiers are, and what they mean. 'public' members are accessible anywhere, 'private' members are accessible only by the same class and friends, etc. What I'm wondering is what, if anything, this equates to in lower-level terms. Are their any post-compilation functional differences between these beyond the high-level restrictions (what can access what) imposed by the language (c++ in this case) they're used in. Another way to put it - if this were a perfect world where programmers always made good choices (like not accessing members that may change later and using only well defined members that should stay the same between implementations), would their be any reason to use these things?

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• How do I stop infinite loop? [closed]

  - by SystemNetworks

  As you see, I have a stack overflow error. I wanted to use a class (goldArmor.java) which has all its own stuffs and uses some booleans, int, double from my main class(play.java). Now I want to call my other class(goldArmor.java) to my main class(play.java). When I press run, it says stackoverflow. How do I fix it? For My goldArmor.java: Play playI = new Play(); This is what I tried: Created another class(connect) to connect from my sub-class to my play.class: goldArmor goldArm = new goldArmor(); THen in my play.java: connect con = new connect();

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• What is the fragile base class problem?

  - by SunilRai86

  What is the fragile base class problem in java?

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• Only one public class per file

  - by abson

  Why is it that only one public class is permitted in a .java file?

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• Alternative to the syntax "MyClass.class.getName()"

  - by Mocha

  Is there any other way of expressing this in Java? MyClass.class.getName()

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• Java EE 6???????????WebLogic Server 12c????

  - by ???02

  Java EE 6?Java SE 7?????????200??????????/???????WebLogic Server 12c??????????????????????????????????????????????????????????????? ?????2??????WebLogic Server 12c???/??????????????????????????????????????????????????????????(???) Eclipse?NetBeans?JDeveloper????IDE?????????? WebLogic Server 12c????????????????????????? Fusion Middleware?????? ????????? Cloud Application Foundation???????? ???????????????????? WebLogic Server 12c????????????????????????/??????????????POJO???????·??????????XML???????????Java EE 6???????????????????WebLogic Server 12c??????????????????????????????? 1????????????????????????????????????????????????NetBeans IDE???Eclipse???Oracle Enterprise Pack for Eclipse 12c????????????Oracle JDeveloper??IDE???????????(JDeveloper???Java EE 6?????)? ???Oracle Enterprise Pack for Eclipse 12c??????????Eclipse????????????Eclipse????????Java EE 6???????????????????????????????Java SE 7????????????????????????Eclipse????WebLogic Server 12c??????Java EE?????????????????? JRockit Mission Control?Eclipse??????? WebLogic Server????????????????????????/??????Oracle JRockit Mission Control (JRMC) 4.1?????????????WebLogic Server 12c????????JRMC???????????????OutOfMemory????????????????????????????????????????????????????????????????????????4.1??????Mac OS X?Solaris?????HotSpot/Solaris?DTrace???????????????????????????????? ????WebLogic Server 12c?????JRMC ?Eclipse??????????????????Eclipse??JRMC????????????????????????????Eclipse?????????????????????????????????????????????????? Maven??????????????????? ????????????????????Apache Maven????????????????????????????????Maven??????????????????????????????????????????????????????????????????????? WebLogic Server???????Maven???????????????WebLogic Server???????????????????????????????????/??/??/?????????Maven??????????? ????????WebLogic Server 12c????????????ZIP????????????????WebLogic Server????????WebLogic????????WebLogic Server?????????/???????????????????????????Maven?????????????????????????????????????????????? ???168MB?ZIP??????????????????????????? ???????Maven???????????????????????????????????ZIP????????????????? ZIP?????????????????????WebLogic Server????????????????WebLogic Server ?????ZIP?????????????????????WebLogic Server?????????????????????????????????????????? ???WebLogic Server 12c??ZIP????????????????168MB??????????????????USB?????????????????????????????? ??ZIP????????????Maven??????????????????????????????????????????????????????????????Maven???????????????????????????????WebLogic Server??????????????????????Maven?????????????????ZIP????????????????????????????????????????? ????????????????????·????????? WebLogic Server 12c???????????????????????????????????????????????????????????·?????????(CAT:Classloader Analysis Tool)?????????? ???Java EE?????Struts?Spring Framework????????????·?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? ??????????????????????CAT????CAT??????????????????????????WebLogic Server????????????????????????????????????/??????????????????????/??????????????????????????????????CAT? “?????”?????????WebLogic Server?????????????? ??????WebLogic Server 12c?????????????????????????????????Java EE???????????????????????????????????????????WebLogic Server 12c???/???????????????????

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• Java Basics: create class object

  - by user1767853

  In C++: class Rectangle { int x, y; public: void set_values (int,int); int area () {return (x*y);} }; int main () { Rectangle rect; rect.set_values (3,4); } In Java: class Rectangle { int x, y; void set_values (int x,int y); int area () {return (x*y);} } public static void main(String[] args) { Rectangle rect=new Rectangle(3,4); } In C++ compiler will create rect object & reserve memory 4 bytes. I want to know How Java is creating object?

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• Java constructor and modify the object properties at runtime

  - by lupin

  Note: This is an assignment Hi, I have the following class/constructor. import java.io.*; class Set { public int numberOfElements = 0; public String[] setElements = new String[5]; public int maxNumberOfElements = 5; // constructor for our Set class public Set(int numberOfE, int setE, int maxNumberOfE) { int numberOfElements = numberOfE; String[] setElements = new String[setE]; int maxNumberOfElements = maxNumberOfE; } // Helper method to shorten/remove element of array since we're using basic array instead of ArrayList or HashSet from collection interface :( static String[] removeAt(int k, String[] arr) { final int L = arr.length; String[] ret = new String[L - 1]; System.arraycopy(arr, 0, ret, 0, k); System.arraycopy(arr, k + 1, ret, k, L - k - 1); return ret; } int findElement(String element) { int retval = 0; for ( int i = 0; i < setElements.length; i++) { if ( setElements[i] != null && setElements[i].equals(element) ) { return retval = i; } retval = -1; } return retval; } void add(String newValue) { int elem = findElement(newValue); if( numberOfElements < maxNumberOfElements && elem == -1 ) { setElements[numberOfElements] = newValue; numberOfElements++; } } int getLength() { if ( setElements != null ) { return setElements.length; } else { return 0; } } String[] emptySet() { setElements = new String[0]; return setElements; } Boolean isFull() { Boolean True = new Boolean(true); Boolean False = new Boolean(false); if ( setElements.length == maxNumberOfElements ){ return True; } else { return False; } } Boolean isEmpty() { Boolean True = new Boolean(true); Boolean False = new Boolean(false); if ( setElements.length == 0 ) { return True; } else { return False; } } void remove(String newValue) { for ( int i = 0; i < setElements.length; i++) { if ( setElements[i].equals(newValue) ) { setElements = removeAt(i,setElements); } } } int isAMember(String element) { int retval = -1; for ( int i = 0; i < setElements.length; i++ ) { if (setElements[i] != null && setElements[i].equals(element)) { return retval = i; } } return retval; } void printSet() { for ( int i = 0; i < setElements.length; i++) { System.out.println("Member elements on index: "+ i +" " + setElements[i]); } } String[] getMember() { String[] tempArray = new String[setElements.length]; for ( int i = 0; i < setElements.length; i++) { if(setElements[i] != null) { tempArray[i] = setElements[i]; } } return tempArray; } Set union(Set x, Set y) { String[] newXtemparray = new String[x.getLength()]; String[] newYtemparray = new String[y.getLength()]; Set temp = new Set(1,20,20); newXtemparray = x.getMember(); newYtemparray = x.getMember(); for(int i = 0; i < newXtemparray.length; i++) { temp.add(newYtemparray[i]); } for(int j = 0; j < newYtemparray.length; j++) { temp.add(newYtemparray[j]); } return temp; } } // This is the SetDemo class that will make use of our Set class class SetDemo { public static void main(String[] args) { //get input from keyboard BufferedReader keyboard; InputStreamReader reader; String temp = ""; reader = new InputStreamReader(System.in); keyboard = new BufferedReader(reader); try { System.out.println("Enter string element to be added" ); temp = keyboard.readLine( ); System.out.println("You entered " + temp ); } catch (IOException IOerr) { System.out.println("There was an error during input"); } /* ************************************************************************** * Test cases for our new created Set class. * ************************************************************************** */ Set setA = new Set(1,10,10); setA.add(temp); setA.add("b"); setA.add("b"); setA.add("hello"); setA.add("world"); setA.add("six"); setA.add("seven"); setA.add("b"); int size = setA.getLength(); System.out.println("Set size is: " + size ); Boolean isempty = setA.isEmpty(); System.out.println("Set is empty? " + isempty ); int ismember = setA.isAMember("sixb"); System.out.println("Element six is member of setA? " + ismember ); Boolean output = setA.isFull(); System.out.println("Set is full? " + output ); setA.printSet(); int index = setA.findElement("world"); System.out.println("Element b located on index: " + index ); setA.remove("b"); setA.emptySet(); int resize = setA.getLength(); System.out.println("Set size is: " + resize ); setA.printSet(); Set setB = new Set(0,10,10); Set SetA = setA.union(setB,setA); SetA.printSet(); } } I have two question here, why I when I change the class property declaration to: class Set { public int numberOfElements; public String[] setElements; public int maxNumberOfElements; // constructor for our Set class public Set(int numberOfE, int setE, int maxNumberOfE) { int numberOfElements = numberOfE; String[] setElements = new String[setE]; int maxNumberOfElements = maxNumberOfE; } I got this error: \ javaprojects>java SetDemo Enter string element to be added a You entered a Exception in thread "main" java.lang.NullPointerException at Set.findElement(Set.java:30) at Set.add(Set.java:43) at SetDemo.main(Set.java:169) Second, on the union method, why the result of SetA.printSet still printing null, isn't it getting back the return value from union method? Thanks in advance for any explaination. lupin

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• Java invalid stream header Problem

  - by David zsl

  Hi all, im writen a client-server app, and now i´m facing a problem that I dont know how to solve: This is the client: try { Socket socket = new Socket(ip, port); ObjectOutputStream ooos = new ObjectOutputStream(socket .getOutputStream()); SendMessage message = new SendMessage(); message.numDoc = value.numDoc; message.docFreq = value.docFreq; message.queryTerms = query; message.startIndex = startIndex; message.count = count; message.multiple = false; message.ips = null; message.ports = null; message.value = true; message.docFreq = value.docFreq; message.numDoc = value.numDoc; ooos.writeObject(message); ObjectInputStream ois = new ObjectInputStream(socket .getInputStream()); ComConstants mensajeRecibido; Object mensajeAux; String mensa = null; byte[] by = null; do { mensajeAux = ois.readObject(); if (mensajeAux instanceof ComConstants) { System.out.println("Thread by Thread has Search Results"); String test; ByteArrayOutputStream testo = new ByteArrayOutputStream(); mensajeRecibido = (ComConstants) mensajeAux; byte[] wag; testo.write( mensajeRecibido.fileContent, 0, mensajeRecibido.okBytes); wag = testo.toByteArray(); if (by == null) { by = wag; } else { int size = wag.length; System.arraycopy(wag, 0, by, 0, size); } } else { System.err.println("Mensaje no esperado " + mensajeAux.getClass().getName()); break; } } while (!mensajeRecibido.lastMessage); //ByteArrayInputStream bs = new ByteArrayInputStream(by.toByteArray()); // bytes es el byte[] ByteArrayInputStream bs = new ByteArrayInputStream(by); ObjectInputStream is = new ObjectInputStream(bs); QueryWithResult[] unObjetoSerializable = (QueryWithResult[])is.readObject(); is.close(); //AQUI TOCARIA METER EL QUICKSORT XmlConverter xce = new XmlConverter(unObjetoSerializable, startIndex, count); String serializedd = xce.runConverter(); tempFinal = serializedd; ois.close(); socket.close(); } catch (Exception e) { e.printStackTrace(); } i++; } And this is the sender: try { QueryWithResult[] outputLine; Operations op = new Operations(); boolean enviadoUltimo=false; ComConstants mensaje = new ComConstants(); mensaje.queryTerms = query; outputLine = op.processInput(query, value); //String c = new String(); //c = outputLine.toString(); //StringBuffer swa = sw.getBuffer(); ByteArrayOutputStream bs= new ByteArrayOutputStream(); ObjectOutputStream os = new ObjectOutputStream (bs); os.writeObject(outputLine); os.close(); byte[] mybytearray = bs.toByteArray(); ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(mybytearray); BufferedInputStream bis = new BufferedInputStream(byteArrayInputStream); int readed = bis.read(mensaje.fileContent,0,4000); while (readed > -1) { mensaje.okBytes = readed; if (readed < ComConstants.MAX_LENGTH) { mensaje.lastMessage = true; enviadoUltimo=true; } else mensaje.lastMessage = false; oos.writeObject(mensaje); if (mensaje.lastMessage) break; mensaje = new ComConstants(); mensaje.queryTerms = query; readed = bis.read(mensaje.fileContent); } if (enviadoUltimo==false) { mensaje.lastMessage=true; mensaje.okBytes=0; oos.writeObject(mensaje); } oos.close(); } catch (Exception e) { e.printStackTrace(); } } And this is the error log: Thread by Thread has Search Results java.io.StreamCorruptedException: invalid stream header: 20646520 at java.io.ObjectInputStream.readStreamHeader(Unknown Source) at java.io.ObjectInputStream.<init>(Unknown Source) at org.tockit.comunication.ServerThread.enviaFicheroMultiple(ServerThread.java:747) at org.tockit.comunication.ServerThread.run(ServerThread.java:129) at java.lang.Thread.run(Unknown Source) Where at org.tockit.comunication.ServerThread.enviaFicheroMultiple(ServerThread.java:747) is this line ObjectInputStream is = new ObjectInputStream(bs); on the 1st code just after while (!mensajeRecibido.lastMessage); Any ideas?

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• How to Stich to Image objects in Java

  - by Imran

  Hi, I have a scenario in which i`m getting a number of tiles (e.g.12) from my mapping server. Now for buffering and offline functions I need to join them all back again so that we have to deal with 1 single image object instead of 12. I ve tried to do it without JAI my code is below. package imagemerge; import java.awt.*; import java.awt.image.*; import java.awt.event.*; public class ImageSticher extends WindowAdapter { Image tile1; Image tile2; Image result; ColorModel colorModel; int width,height,widthr,heightr; //int t1,t2; int t12[]; public ImageSticher() { } public ImageSticher (Image img1,Image img2,int w,int h) { tile1=img1; tile2=img2; width=w; height=h; colorModel=ColorModel.getRGBdefault(); } public Image horizontalStich() throws Exception { widthr=width*2; heightr=height; t12=new int[widthr * heightr]; int t1[]=new int[width*height]; PixelGrabber p1 =new PixelGrabber(tile1, 0, 0, width, height, t1, 0, width); p1.grabPixels(); int t2[]=new int[width*height]; PixelGrabber p2 =new PixelGrabber(tile2, 0, 0, width, height, t1, 0, width); p2.grabPixels(); int y, x, rp, rpi; int red1, red2, redr; int green1, green2, greenr; int blue1, blue2, bluer; int alpha1, alpha2, alphar; for(y=0;y<heightr;y++) { for(x=0;x<widthr;x++) { //System.out.println(x); rpi=y*widthr+x; // index of resulting pixel; rp=0; //initializing resulting pixel System.out.println(rpi); if(x<(widthr/2)) // x is less than width , copy first tile { //System.out.println("tile1="+x); blue1 = t1[rpi] & 0x00ff; // ERROR occurs here green1=(t1[rpi] >> 8) & 0x00ff; red1=(t1[rpi] >> 16) & 0x00ff; alpha1 = (t1[rpi] >> 24) & 0x00ff; redr = (int)(red1 * 1.0); // copying red band pixel into redresult,,,,1.0 is the alpha valye redr = (redr < 0)?(0):((redr>255)?(255):(redr)); greenr = (int)(green1 * 1.0); // redr = (int)(red1 * 1.0); // greenr = (greenr < 0)?(0):((greenr>255)?(255):(greenr)); bluer = (int)(blue1 * 1.0); bluer = (bluer < 0)?(0):((bluer>255)?(255):(bluer)); alphar = 255; //resulting pixel computed rp = (((((alphar << 8) + (redr & 0x0ff)) << 8) + (greenr & 0x0ff)) << 8) + (bluer & 0x0ff); } else // index is ahead of half way...copy second tile { blue2 = t2[rpi] & 0x00ff; // blue band bit of first tile green2=(t2[rpi] >> 8) & 0x00ff; red2=(t2[rpi] >> 16) & 0x00ff; alpha2 = (t2[rpi] >> 24) & 0x00ff; redr = (int)(red2 * 1.0); // copying red band pixel into redresult,,,,1.0 is the alpha valye redr = (redr < 0)?(0):((redr>255)?(255):(redr)); greenr = (int)(green2 * 1.0); // redr = (int)(red2 * 1.0); // greenr = (greenr < 0)?(0):((greenr>255)?(255):(greenr)); bluer = (int)(blue2 * 1.0); bluer = (bluer < 0)?(0):((bluer>255)?(255):(bluer)); alphar = 255; //resulting pixel computed rp = (((((alphar << 8) + (redr & 0x0ff)) << 8) + (greenr & 0x0ff)) << 8) + (bluer & 0x0ff); } t12[rpi] = rp; // copying resulting pixel in the result int array which will be converted to image } } MemoryImageSource mis; if (t12!=null) { mis = new MemoryImageSource(widthr, heightr, colorModel, t12, 0, widthr); result = Toolkit.getDefaultToolkit().createImage(mis); return result; } return null; } } now to check the my theory Im trying to join or stich two tiles horizontaly but im getting the error : java.lang.ArrayIndexOutOfBoundsException: 90000 at imagemerge.ImageSticher.horizontalStich(ImageSticher.java:69) at imageStream.ImageStream.getImage(ImageStream.java:75) at imageStream.ImageStream.main(ImageStream.java:28) is there some kind of limitation because when stiching two images of 300 x 300 horizontally it means the resulting image will be 600 x 300 ... that would make 180000 index size but its giving error at 90000, what am I doing wrong here

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• Tomcat stops responding to JK requests

  - by Bruno Reis

  Hello. I have a nasty issue with load-balanced Tomcat servers that are hanging up. Any help would be greatly appreciated. The system I'm running Tomcat 6.0.26 on HotSpot Server 14.3-b01 (Java 1.6.0_17-b04) on three servers sitting behind another server that acts as load balancer. The load balancer runs Apache (2.2.8-1) + MOD_JK (1.2.25). All of the servers are running Ubuntu 8.04. The Tomcat's have 2 connectors configured: an AJP one, and a HTTP one. The AJP is to be used with the load balancer, while the HTTP is used by the dev team to directly connect to a chosen server (if we have a reason to do so). I have Lambda Probe 1.7b installed on the Tomcat servers to help me diagnose and fix the problem soon to be described. The problem Here's the problem: after about 1 day the application servers are up, JK Status Manager starts reporting status ERR for, say, Tomcat2. It will simply get stuck on this state, and the only fix I've found so far is to ssh the box and restart Tomcat. I must also mention that JK Status Manager takes a lot longer to refresh when there's a Tomcat server in this state. Finally, the "Busy" count of the stuck Tomcat on JK Status Manager is always high, and won't go down per se -- I must restart the Tomcat server, wait, then reset the worker on JK. Analysis Since I have 2 connectors on each Tomcat (AJP and HTTP), I still can connect to the application through the HTTP one. The application works just fine like this, very, very fast. That is perfectly normal, since I'm the only one using this server (as JK stopped delegating requests to this Tomcat). To try to better understand the problem, I've taken a thread dump from a Tomcat which is not responding anymore, and from another one that has been restarted recently (say, 1 hour before). The instance that is responding normally to JK shows most of the TP-ProcessorXXX threads in "Runnable" state, with the following stack trace: java.net.SocketInputStream.socketRead0 ( native code ) java.net.SocketInputStream.read ( SocketInputStream.java:129 ) java.io.BufferedInputStream.fill ( BufferedInputStream.java:218 ) java.io.BufferedInputStream.read1 ( BufferedInputStream.java:258 ) java.io.BufferedInputStream.read ( BufferedInputStream.java:317 ) org.apache.jk.common.ChannelSocket.read ( ChannelSocket.java:621 ) org.apache.jk.common.ChannelSocket.receive ( ChannelSocket.java:559 ) org.apache.jk.common.ChannelSocket.processConnection ( ChannelSocket.java:686 ) org.apache.jk.common.ChannelSocket$SocketConnection.runIt ( ChannelSocket.java:891 ) org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run ( ThreadPool.java:690 ) java.lang.Thread.run ( Thread.java:619 ) The instance that is stuck show most (all?) of the TP-ProcessorXXX threads in "Waiting" state. These have the following stack trace: java.lang.Object.wait ( native code ) java.lang.Object.wait ( Object.java:485 ) org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run ( ThreadPool.java:662 ) java.lang.Thread.run ( Thread.java:619 ) I don't know of the internals of Tomcat, but I would infer that the "Waiting" threads are simply threads sitting on a thread pool. So, if they are threads waiting inside of a thread pool, why wouldn't Tomcat put them to work on processing requests from JK? Solution? So, as I've stated before, the only fix I've found is to stop the Tomcat instance, stop the JK worker, wait the latter's busy count slowly go down, start Tomcat again, and enable the JK worker once again. What is causing this problem? How should I further investigate it? What can I do to solve it? Thanks in advance.

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• Adding an annotation to a runtime generated method/class using Javassist

  - by Idan K

  I'm using Javassist to generate a class foo, with method bar, but I can't seem to find a way to add an annotation (the annotation itself isn't runtime generated) to the method. The code I tried looks like this: ClassPool pool = ClassPool.getDefault(); // create the class CtClass cc = pool.makeClass("foo"); // create the method CtMethod mthd = CtNewMethod.make("public Integer getInteger() { return null; }", cc); cc.addMethod(mthd); ClassFile ccFile = cc.getClassFile(); ConstPool constpool = ccFile.getConstPool(); // create the annotation AnnotationsAttribute attr = new AnnotationsAttribute(constpool, AnnotationsAttribute.visibleTag); Annotation annot = new Annotation("MyAnnotation", constpool); annot.addMemberValue("value", new IntegerMemberValue(ccFile.getConstPool(), 0)); attr.addAnnotation(annot); ccFile.addAttribute(attr); // generate the class clazz = cc.toClass(); // length is zero java.lang.annotation.Annotation[] annots = clazz.getAnnotations(); And obviously I'm doing something wrong since annots is an empty array. This is how the annotation looks like: @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD) public @interface MyAnnotation { int value(); }

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• Overriding equals method without breaking symmetry in a class that has a primary key

  - by Kosta

  Hi, the answer to this question is probably "not possible", but let me ask regardless :) Assuming we have a very simple JAVA class that has a primary key, for example: class Person { String ssid; String name; String address; ... } Now, I want to store people in a collection, meaning I will have to override the equals method. Not a completely trivial matter, but on a bare basis I will have something along the lines of: @Override public boolean equals (Object other) { if(other==this) return true; if(!other.getClass().equals(this.getClass()) return false; Person otherPerson = (Person)other; if(this.ssid.equals(otherPerson.getSsid()) return true; } Excuse any obvious blunders, just typing this out of my head. Now, let's say later on in the application I have a ssid I obtained through user input. If I want to compare my ssid to a Person, I would have to call something like: String mySsid = getFromSomewhere(); Person myPerson = getFromSomewhere(); if(myPerson.equals(new Person(mySsid)) doSomething(); This means I have to create a convenience constructor to create a Person based on ssid (if I don't already have one), and it's also quite verbose. It would be much nicer to simply call myPerson.equals(mySsid) but if I added a string comparison to my Person equals class, that would break the symmetry property, since the String hasn't got a clue on how to compare itself to a Person. So finally, the big question, is there any way to enable this sort of "shorthand" comparisons using the overriden equals method, and without breaking the symmetry rule? Thanks for any thoughts on this!

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• Android Activity ClassNotFoundException - tried everything

  - by Matthew Rathbone

  I've just refactored an app into a framework library and an application, but now when I try and start the app in the emulator I get the following error stack trace: 06-02 18:22:35.529: E/AndroidRuntime(586): FATAL EXCEPTION: main 06-02 18:22:35.529: E/AndroidRuntime(586): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.matthewrathbone.eastersays/com.matthewrathbone.eastersays.EasterSimonSaysActivity}: java.lang.ClassNotFoundException: com.matthewrathbone.eastersays.EasterSimonSaysActivity in loader dalvik.system.PathClassLoader[/data/app/com.matthewrathbone.eastersays-1.apk] 06-02 18:22:35.529: E/AndroidRuntime(586): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585) 06-02 18:22:35.529: E/AndroidRuntime(586): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 06-02 18:22:35.529: E/AndroidRuntime(586): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 06-02 18:22:35.529: E/AndroidRuntime(586): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 06-02 18:22:35.529: E/AndroidRuntime(586): at android.os.Handler.dispatchMessage(Handler.java:99) 06-02 18:22:35.529: E/AndroidRuntime(586): at android.os.Looper.loop(Looper.java:123) 06-02 18:22:35.529: E/AndroidRuntime(586): at android.app.ActivityThread.main(ActivityThread.java:4627) 06-02 18:22:35.529: E/AndroidRuntime(586): at java.lang.reflect.Method.invokeNative(Native Method) 06-02 18:22:35.529: E/AndroidRuntime(586): at java.lang.reflect.Method.invoke(Method.java:521) 06-02 18:22:35.529: E/AndroidRuntime(586): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 06-02 18:22:35.529: E/AndroidRuntime(586): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 06-02 18:22:35.529: E/AndroidRuntime(586): at dalvik.system.NativeStart.main(Native Method) 06-02 18:22:35.529: E/AndroidRuntime(586): Caused by: java.lang.ClassNotFoundException: com.matthewrathbone.eastersays.EasterSimonSaysActivity in loader dalvik.system.PathClassLoader[/data/app/com.matthewrathbone.eastersays-1.apk] 06-02 18:22:35.529: E/AndroidRuntime(586): at dalvik.system.PathClassLoader.findClass(PathClassLoader.java:243) 06-02 18:22:35.529: E/AndroidRuntime(586): at java.lang.ClassLoader.loadClass(ClassLoader.java:573) 06-02 18:22:35.529: E/AndroidRuntime(586): at java.lang.ClassLoader.loadClass(ClassLoader.java:532) 06-02 18:22:35.529: E/AndroidRuntime(586): at android.app.Instrumentation.newActivity(Instrumentation.java:1021) 06-02 18:22:35.529: E/AndroidRuntime(586): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577) 06-02 18:22:35.529: E/AndroidRuntime(586): ... 11 more Usually this means that the manifest file is wrong in some way, but I've double checked everything I can think of. Here is my activity class: package com.matthewrathbone.eastersays; import android.os.Bundle; import com.rathboma.simonsays.Assets.Season; import com.rathboma.simonsays.SeasonPicker; import com.rathboma.simonsays.SimonSaysActivity; public class EasterSimonSaysActivity extends SimonSaysActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } @Override protected void onDestroy() { // TODO Auto-generated method stub super.onDestroy(); } @Override public SeasonPicker getSeasonPicker() { return new SeasonPicker(){ @Override public Season getSeason() { // TODO Auto-generated method stub return Season.EASTER; } }; } } As you can see, it's listed correctly in the manifest: <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.matthewrathbone.eastersays" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="7" android:targetSdkVersion="15" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:name=".EasterSimonSaysActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest> I have no idea how to fix this, and would appreciate any help. I've scanned many similar questions on SO without seeing this particular behavior. More info: I've checked inside the generated APK and the class has an entry in the classes.dex file I've tried cleaning/building the project in eclipse I've tried using a totally new device image that doesn't have a copy of the APK on it already I've changed the library project into a regular java, then changed back into an android project, no difference

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• How to determine errors in java

  - by user225269

  I'm just a java beginner. Do you have any tips there on how to determine errors. I'm trying to connect to mysql derby database. I don't know how to determine the error, there is no red line, but there is a message box that shows up when I try to run the program. All I want to do is to display the first record in the database. All I get is this in the output: E:\Users\users.netbeans\6.8\var\cache\executor-snippets\run.xml:45: package Employees; import java.sql.Statement; import javax.swing.JOptionPane; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.sql.ResultSet; /** * * @author Nrew */ public class Students extends javax.swing.JFrame { Connection con; Statement stmt; ResultSet rs; /** Creates new form Students */ public Students() { initComponents(); DoConnect(); } public void DoConnect(){ try { String host= "jdbc:derby://localhost:1527/YURA"; String uname = "bart"; String pword = "12345"; con = DriverManager.getConnection(host, uname, pword); stmt = con.createStatement( ); String SQL = "SELECT * FROM APP.XROSS"; rs = stmt.executeQuery(SQL); rs.next(); rs.next( ); int ids = rs.getInt("IDNUM"); String idz = Integer.toString(ids); String fname = rs.getString("FNAME"); String lname = rs.getString("LNAME"); String course = rs.getString("COURSE"); String skul = rs.getString("SCHOOL"); String gen = rs.getString("GENDER"); TextIDNUM.setText(idz); TextFNAME.setText(fname); TextLNAME.setText(lname); textCOURSE.setText(course); textSCHOOL.setText(skul); textGENDER.setText(gen); } catch (SQLException err) { JOptionPane.showMessageDialog(Students.this, err.getMessage()); } } /** This method is called from within the constructor to * initialize the form. * WARNING: Do NOT modify this code. The content of this method is * always regenerated by the Form Editor. */ @SuppressWarnings("unchecked") // <editor-fold defaultstate="collapsed" desc="Generated Code"> private void initComponents() { TextIDNUM = new javax.swing.JTextField(); TextFNAME = new javax.swing.JTextField(); TextLNAME = new javax.swing.JTextField(); textCOURSE = new javax.swing.JTextField(); textSCHOOL = new javax.swing.JTextField(); textGENDER = new javax.swing.JTextField(); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); getContentPane().setLayout(layout); layout.setHorizontalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGap(116, 116, 116) .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false) .addComponent(textGENDER, javax.swing.GroupLayout.Alignment.LEADING) .addComponent(textSCHOOL, javax.swing.GroupLayout.Alignment.LEADING) .addComponent(textCOURSE, javax.swing.GroupLayout.Alignment.LEADING) .addComponent(TextLNAME, javax.swing.GroupLayout.Alignment.LEADING) .addComponent(TextFNAME, javax.swing.GroupLayout.Alignment.LEADING) .addComponent(TextIDNUM, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, 151, Short.MAX_VALUE)) .addContainerGap(243, Short.MAX_VALUE)) ); layout.setVerticalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGap(37, 37, 37) .addComponent(TextIDNUM, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(18, 18, 18) .addComponent(TextFNAME, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(18, 18, 18) .addComponent(TextLNAME, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addGap(18, 18, 18) .addComponent(textCOURSE, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED) .addComponent(textSCHOOL, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED) .addComponent(textGENDER, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addContainerGap(67, Short.MAX_VALUE)) ); pack(); }// </editor-fold> /** * @param args the command line arguments */ public static void main(String args[]) { java.awt.EventQueue.invokeLater(new Runnable() { public void run() { new Students().setVisible(true); } }); } // Variables declaration - do not modify private javax.swing.JTextField TextFNAME; private javax.swing.JTextField TextIDNUM; private javax.swing.JTextField TextLNAME; private javax.swing.JTextField textCOURSE; private javax.swing.JTextField textGENDER; private javax.swing.JTextField textSCHOOL; // End of variables declaration }

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• Ant + JUnit: NoClassDefFoundError

  - by K-Boo

  Ok, I'm frustrated! I've hunted around for a good number of hours and am still stumped. Environment: WinXP, Eclipse Galileo 3.5 (straight install - no extra plugins). So, I have a simple JUnit test. It runs fine from it's internal Eclipse JUnit run configuration. This class has no dependencies on anything. To narrow this problem down as much as possible it simply contains: @Test public void testX() { assertEquals("1", new Integer(1).toString()); } No sweat so far. Now I want to take the super advanced step of running this test case from within Ant (the final goal is to integrate with Hudson). So, I create a build.xml: <project name="Test" default="basic"> <property name="default.target.dir" value="${basedir}/target" /> <property name="test.report.dir" value="${default.target.dir}/test-reports" /> <target name="basic"> <mkdir dir="${test.report.dir}" /> <junit fork="true" printSummary="true" showOutput="true"> <formatter type="plain" /> <classpath> <pathelement path="${basedir}/bin "/> </classpath> <batchtest fork="true" todir="${test.report.dir}" > <fileset dir="${basedir}/bin"> <include name="**/*Test.*" /> </fileset> </batchtest> </junit> </target> </project> ${basedir} is the Java project name in the workspace that contains the source, classes and build file. All .java's and the build.xml are in ${basedir}/src. The .class files are in ${basedir}/bin. I have added eclipse-install-dir/plugins/org.junit4_4.5.0.v20090423/junit.jar to the Ant Runtime Classpath via Windows / Preferences / Ant / Runtime / Contributed Entries. ant-junit.jar is in Ant Home Entries. So, what happens when I run this insanely complex target? My report file contains: Testsuite: com.xyz.test.RussianTest Tests run: 1, Failures: 0, Errors: 1, Time elapsed: 0 sec Testcase: initializationError took 0 sec Caused an ERROR org/hamcrest/SelfDescribing java.lang.NoClassDefFoundError: org/hamcrest/SelfDescribing at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(Unknown Source) at java.security.SecureClassLoader.defineClass(Unknown Source) at java.net.URLClassLoader.defineClass(Unknown Source) at java.net.URLClassLoader.access$000(Unknown Source) at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClassInternal(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) Caused by: java.lang.ClassNotFoundException: org.hamcrest.SelfDescribing at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClassInternal(Unknown Source) What is this org.hamcrest.SelfDescribing class? Something to do with mocks? OK, fine. But why the dependency? I'm not doing anything at all with it. This is literally a Java project with no dependencies other than JUnit. Stumped (and frustrated)!!

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• Does Java have dynamic variables for class members?

  - by Arvanem

  Hi folks, I am wondering whether it is possible to make dynamic variables in Java. In other words, variables that change depending on my instructions. FYI, I am making a trading program. A given merchant will have an array of items for sale for various prices. The dynamism I am calling for comes in because each category of items for sale has its own properties. For example, a book item has two properties: int pages, and boolean hardCover. In contrast, a bookmark item has one property, String pattern. Here are skeleton snippets of code so you can see what I am trying to do: public class Merchants extends /* certain parent class */ { // only 10 items for sale to begin with Stock[] itemsForSale = new Stock[10]; // Array holding Merchants public static Merchants[] merchantsArray = new Merchants[maxArrayLength]; // method to fill array of stock goes here } and public class Stock { int stockPrice; int stockQuantity; String stockType; // e.g. book and bookmark // Dynamic variables here, but they should only be invoked depending on stockType int pages; boolean hardCover; String pattern; }

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