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  • how does serializable work in java?

    - by Karl Trumstedt
    If I have an instance of a class that I store in a session I need to make it serializable. This class has a static variable, will this be serialized in every instance stored? The static variable is a reference to a cache containing a lot of data in the background. Will all of this data be serialized? If so, it seems preferable to make this variable transient and re-fetch the cache instance each time the instance is restored. Maybe not store the cache instance at all in the class. Will the constructor execute when a class is restored from a serialized state? if not is there any other method I can use to re-instate a transient variable?

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  • Reverse a given sentence in java

    - by giri
    This was the question asked me in amazon interview. I could not solve the problem properly, Write a program to reverse a given sentence like "This is interview question" the output must be "question interview is this".Can any tell me how to get this done? Thanks in advance

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  • Java blocking socket returning incomplete ByteBuffer

    - by evandro-carrenho
    I have a socketChannel configured as blocking, but when reading byte buffers of 5K from this socket, I get an incomplete buffer sometimes. ByteBuffer messageBody = ByteBuffer.allocate(5*1024); messageBody.mark(); messageBody.order(ByteOrder.BIG_ENDIAN); int msgByteCount = channel.read(messageBody); Ocasionally, messageBody is not completely filled and channel.read() does not return -1 or an exception, but the actual number of bytes read (which is less than 5k). Has anyone experienced a similar problem?

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  • Java: Reflection against casting when you know superclass

    - by Ema
    I don't know exactly how to define my doubt so please be patient if the question has already been asked. Let's say I have to dinamically instantiate an object. This object will surely be instance of a subclass of a known, immutable class A. I can obtain dinamically the specific implementation class. Would it be better to use reflection exactly as if I didn't know anything about the target class, or would it be preferrable/possible to do something like: A obj = (Class.forName("com.package.Sub-A")) new A(); where Sub-A extends A ? The purpose would be to avoid reflection overhead times... Thank you in advance.

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  • java /TableModel of Objects/Update Object"

    - by Tomás Ó Briain
    I've a collection of Stock objects that I'm updating about 10/15 variables for in real-time. I'm accessing each Stock by its ID in the collection. I'm also trying to display this in a JTable and have implemented an AbstractTablemodel. It's not working too well. I've a RowMap that I add each ID to as Stocks are added to the TableModel. To update the prices and variables of all the stocks in the TableModel, I want to send a Stock object to an updateModel(Stock s) method. I can find the relevant row by searching the map, but how do I handle this nicely, so I don't have to start iterating through table columns and comparing the values of the cells to the variables of the object to see whether there are any differences?? Basically, i want to send a Stock object to the TableModel and update cells if there are changes and do nothing if there aren't. Any ideas about how to implement a TableModel that might do this? Any pointeres at all would be appreciated. Thanks.

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  • Java regex to get part number

    - by Blankman
    I have HTML that I need to extract a part number from, the HTML looks like: javascript:selectItem('ABC123 1', '..... I need to get the ABC123 from the above. My code snippet: Patterp p = Pattern.Compile("?????"); Matcher m = p.matcher(html); if(m.find()) partNumber = m.group(1).trim(); BTW, in the pattern, how do I escape for the character ( I now for quotes I do \" thanks allot!

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  • Java: refactoring static constants

    - by akf
    We are in the process of refactoring some code. There is a feature that we have developed in one project that we would like to now use in other projects. We are extracting the foundation of this feature and making it a full-fledged project which can then be imported by its current project and others. This effort has been relatively straight-forward but we have one headache. When the framework in question was originally developed, we chose to keep a variety of constant values defined as static fields in a single class. Over time this list of static members grew. The class is used in very many places in our code. In our current refactoring, we will be elevating some of the members of this class to our new framework, but leaving others in place. Our headache is in extracting the foundation members of this class to be used in our new project, and more specifically, how we should address those extracted members in our existing code. We know that we can have our existing Constants class subclass this new project's Constants class and it would inherit all of the parent's static members. This would allow us to effect the change without touching the code that uses these members to change the class name on the static reference. However, the tight coupling inherent in this choice doesn't feel right. before: public class ConstantsA { public static final String CONSTANT1 = "constant.1"; public static final String CONSTANT2 = "constant.2"; public static final String CONSTANT3 = "constant.3"; } after: public class ConstantsA extends ConstantsB { public static final String CONSTANT1 = "constant.1"; } public class ConstantsB { public static final String CONSTANT2 = "constant.2"; public static final String CONSTANT3 = "constant.3"; } In our existing code branch, all of the above would be accessible in this manner: ConstantsA.CONSTANT2 I would like to solicit arguments about whether this is 'acceptable' and/or what the best practices are.

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  • How to strip specific contents of a String in Java

    - by user2974877
    So I have a string, and I want to strip out some parts of it using, for example, the firt and last characters of the "interesting" part. String dirty = "$!$!%!%$something interesting&!!$!%$something interesting2"; And the output something like: String clean = "something interesting:something interesting2"; Note: The code needs to work without knowing the random part, changing everytime the program runs. I researched and only found code that does it, but only knowing the random segment.

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  • Update music file details - Java.

    - by Desorder
    Hi all, Well, I'm a music fan guy, and now with my 18000 music collection, it's getting very hard to maintain. So, I would like to ask I could of question to help to write an app to maintain it for me. 1- How can I access a music file and read details of it? I mean, I would like to write some code and passing the directory, my app would read all the music files (understand mp3 files) and with that I would like to access details like title, artist, length and so on... 2- Is there a public source that I could access and update my file? A webservice somewhere that I could connect, query some information based on song name, or artist or whatever. I would like to achieve a final result of given a directory, my app would read the file, collect some information and query the source for a complete list of detail and update my file. Thank you guys for any help...

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  • What is the best way to automated (integration) test with java with OpenId4Java against real OpenIdP

    - by mP
    I would like to do a bit more than manually test my openid glue code which happens to use the openid4java library. My goals would be to be able to run it within my IDE with a bunch of tests using Junit or similar. Selenium & tomcat I was thinking of using selenium and a tomcat but thats not exactly a nice approach as this is a bit heavy and not really lightweight. httpunit A solution with http-unit is incomplete because it doesnt really fit with the redirect to my openid provider, authenticate and redirect back. Perhaps i am wrong but this looks like it could get quite involved just to make sure this works. Mocks My last solution is to mock everything and assume thats its accurate and works. If google or yahoo ever change in some way, then ill have to verify manually. The approach is simple but with a major flaw.

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  • JAVA: Can't get context parameters in Filter

    - by DaTval
    Hello, I have a filter and parameters in web.xml web.xml is like this: <filter> <description> </description> <display-name>AllClassFilter</display-name> <filter-name>AllClassFilter</filter-name> <filter-class>com.datval.homework.AllClassFilter</filter-class> <init-param> <param-name>DB_URL</param-name> <param-value>jdbc:derby:C:/Users/admin/workspace/homework03/homework/databases/StudentsDB;create=true</param-value> </init-param> <init-param> <param-name>DB_DIALECT</param-name> <param-value>org.hibernate.dialect.DerbyDialect</param-value> </init-param> <init-param> <param-name>DB_DRIVER</param-name> <param-value>org.apache.derby.jdbc.EmbeddedDriver</param-value> </init-param> </filter> mapping is working well. But I can't get this parameters in my filter. public void init(FilterConfig config) throws ServletException { // TODO Auto-generated method stub debugMessage = config.getInitParameter("debugMessage"); ctx = config.getServletContext(); } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // TODO Auto-generated method stub // place your code here ctx.log("Start - " + debugMessage); String myDbUrl = ctx.getInitParameter("DB_URL"); String DB_DIALECT = ctx.getInitParameter("DB_DIALECT"); String DB_DRIVER = ctx.getInitParameter("DB_DRIVER"); Map<String,String> pr = new HashMap<String,String>(); pr.put("hibernate.connection.url", myDbUrl); pr.put("hibernate.dialect", DB_DIALECT); pr.put("hibernate.connection.driver_class", DB_DRIVER); EntityManagerFactory emf = Persistence.createEntityManagerFactory("students",pr); EntityManager em = emf.createEntityManager(); request.setAttribute("em", em); chain.doFilter(request, response); em.close(); ctx.log("end - " + debugMessage); } I have checked and myDbUrl is null. What I'm doing wrong? Any idea? Sorry about code, I will change it later :)

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  • synchronized in java - Proper use

    - by ZoharYosef
    I'm building a simple program to use in multi processes (Threads). My question is more to understand - when I have to use a reserved word synchronized? Do I need to use this word in any method that affects the bone variables? I know I can put it on any method that is not static, but I want to understand more. thank you! here is the code: public class Container { // *** data members *** public static final int INIT_SIZE=10; // the first (init) size of the set. public static final int RESCALE=10; // the re-scale factor of this set. private int _sp=0; public Object[] _data; /************ Constructors ************/ public Container(){ _sp=0; _data = new Object[INIT_SIZE]; } public Container(Container other) { // copy constructor this(); for(int i=0;i<other.size();i++) this.add(other.at(i)); } /** return true is this collection is empty, else return false. */ public synchronized boolean isEmpty() {return _sp==0;} /** add an Object to this set */ public synchronized void add (Object p){ if (_sp==_data.length) rescale(RESCALE); _data[_sp] = p; // shellow copy semantic. _sp++; } /** returns the actual amount of Objects contained in this collection */ public synchronized int size() {return _sp;} /** returns true if this container contains an element which is equals to ob */ public synchronized boolean isMember(Object ob) { return get(ob)!=-1; } /** return the index of the first object which equals ob, if none returns -1 */ public synchronized int get(Object ob) { int ans=-1; for(int i=0;i<size();i=i+1) if(at(i).equals(ob)) return i; return ans; } /** returns the element located at the ind place in this container (null if out of range) */ public synchronized Object at(int p){ if (p>=0 && p<size()) return _data[p]; else return null; }

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  • Java Timer not working

    - by Jacob
    I have an Image named worldImageToUse and I have a Timer that is supposed to toggle worldImageToUse between two images every 1 second. But it does not seem to work. Help Please? public void startWorldImageFlash() { worldImageFlashTimer = new Timer(); TimerTask task = new TimerTask() { @Override public void run() { if(worldImageToUse == worldImage) setWorldImageBW(); if(worldImageToUse == worldImageBW) setWorldImageColor(); } }; worldImageFlashTimer.scheduleAtFixedRate(task, 0, 1000); } public void stopWorldImageFlash() { worldImageFlashTimer.cancel(); setWorldImageColor(); }

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  • Need Java Swing equivalent of "scrollIntoView" from Browser DOM

    - by bgould
    I have a JPanel with several levels of child components, also with a JScrollPane. I'm placing a focus listener on some of the child components to add some behavior to those components, but I would also like to have that component scroll into the JPanel's viewport when focus is gained. My question is, does anyone have a general purpose function to do this, similar to the browser DOM function "scrollIntoView"? I've tried muddling through this with various inputs to JComponent.scrollRectToVisible but I guess I haven't figured out the magic word. Thanks in advance.

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  • Java: Comparing a class with another within that class using a my own .equals

    - by user1670252
    I am making a method .equals replacing the equals method used. It accepts a object. I want it to check if that object equals the class that runs the .equals class. I know I want to compare all the private methods I have to that object. Is there a way to do this without making another private class to get the private variables from the object? How do I do this to compare equality not identity? I am stuck on this. Do i have to use == to compare? Also looking online i see others use recursion. If this is the way i have to do it can you show and explain it to me? so an example i have public boolean equals(Object o) { this is in a class we will call bobtheBuilder (first thing to pop in my head) I want to check if the object o is equal to the class he has private object array and a private int. I assume I want to check if the array and int of this class equal the array and int of the object.

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  • Extract two double Values from String using RegEx in Java

    - by tzippy
    I am reading a file by line and need to extract latitude and longitude from it. This how lines can looks: DE 83543 Rott am Inn Bayern BY Oberbayern Landkreis Rosenheim 47.983 12.1278 DE 21147 Hamburg Hamburg HH Kreisfreie Stadt Hamburg 53.55 10 What's for sure is, there are no dots surrounded by digits except for the ones representing the doubles. Unfortunately there are Values without a dot, so it's probably best to check for numbers from the end of the String. thanks for your help!

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  • Need a Java based interruptible timer thread

    - by LambeauLeap
    I have a Main Program which is running a script on the target device(smart phone) and in a while loop waiting for stdout messages. However in this particular case, some of the heartbeat messages on the stdout could be spaced almost 45secs to a 1minute apart. something like: stream = device.runProgram(RESTORE_LOGS, new String[] {}); stream.flush(); String line = stream.readLine(); while (line.compareTo("") != 0) { reporter.commentOnJob(jobId, line); line = stream.readLine(); } So, I want to be a able to start a new interruptible thread after reading line from stdout with a required a sleep window. Upon being able to read a new line, I want to be able to interrupt/stop(having trouble killing the process), handle the newline of stdout text and restart a process. And it the event I am not able to read a line within the timer window(say 45secs) I want to a way to get out of my while loop either. I already tried the thread.run, thread.interrupt approach. But having trouble killing and starting a new thread. Is this the best way out or am I missing something obvious?

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  • Read text file in java

    - by user326091
    Hi, I have a text file. I would like to retrieve the content from one line to another line. For example, the file may be 200K lines. I want to read the content from line 78 to line 2735. Since the file may be very large, I do not want to read the whole content into the memory. thanks Frank

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  • java: converting part of a ByteBuffer to a string

    - by Jason S
    I have a ByteBuffer containing bytes that were derived by String.getBytes(charsetName), where "containing" means that the string comprises the entire sequence of bytes between the ByteBuffer's position() and limit(). What's the best way for me to get the string back? (assuming I know the encoding charset) Is there anything better than the following (which seems a little clunky) byte[] ba = new byte[bbuf.remaining()]; bbuf.get(ba); try { String s = new String(ba, charsetName); } catch (UnsupportedEncodingException e) { /* take appropriate action */ }

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