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  • Gracefully avoiding NullPointerException in Java

    - by Yuval A
    Consider this line: if (object.getAttribute("someAttr").equals("true")) { // .... Obviously this line is a potential bug, the attribute might be null and we will get a NullPointerException. So we need to refactor it to one of two choices: First option: if ("true".equals(object.getAttribute("someAttr"))) { // .... Second option: String attr = object.getAttribute("someAttr"); if (attr != null) { if (attr.equals("true")) { // .... The first option is awkward to read but more concise, while the second one is clear in intent, but verbose. Which option do you prefer in terms of readability?

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  • Ask StackOverFlow : Canny a LightWeight Authorization library in Java

    - by eltados
    In the course of my work i need to develop an authorization engine ( i'm already authenticated and i check access of a user to an action ) in order to store all the authorization logic inside a same place and be able to reuse it and i have created the mini library. http://github.com/eltados/canny (updated) what do you think about it? What are the limits of my approch ? Do you understand the benefit or it? Is there any lightweight Authorization engine library i could have a look at? I had a look at spring security and it does not really answer my requirement. The main idea is that i want to be able to reuse the same code to controll access in the controllers and the views.

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  • Java heap size - will this work?

    - by UnCon
    Hi, I try this with NetBeans desktop application template - increasing heapsize (to 512 MiB) of executed .jar file. (I believe that NetBeans uses Singleton app by default - SingleFrameView) Will it work? public static void main(String[] args) { if (args == null) { args = new String[1]; args[0] = "Xmx512m"; } else { String[] tempArgs = new String[args.length+1]; for (int i=0; i<args.length; i++) { tempArgs[i] = args[i]; } tempArgs[tempArgs.length-1] = "Xmx512m"; args = tempArgs; } launch(MyApp.class, args); } }

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  • Shift operator in Java bizarre program output

    - by Umesh Kacha
    I came across the following program and it behaving in unexpected manner. public class ShiftProgram { public static void main(String[] args) { int i = 0; while(-1 << i != 0) i++; System.out.println(i); } } If we think about this program output, when it reaches 32 while loop condition should return false and terminate and it should print 32. If you ran this program, it does not print anything but goes into an infinite loop. Any idea whats going on? Thank you in advance.

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  • Java days of week calculation

    - by Shahid
    I have an Enum for Days of week (with Everyday, weekend and weekdays) as follows where each entry has an int value. public enum DaysOfWeek { Everyday(127), Weekend(65), Weekdays(62), Monday(2), Tuesday(4), Wednesday(8), Thursday(16), Friday(32), Saturday(64), Sunday(1); private int bitValue; private DaysOfWeek(int n){ this.bitValue = n; } public int getBitValue(){ return this.bitValue; } } Given a TOTAL of any combination of the entries, what would be the simplest way to calculate all individual values and make an arraylist from it. For example given the number 56 (i.e. Wed+Thur+Fri), how to calculate the list of individual values.

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  • Java BoxLayout alignment issue

    - by ManInMoon
    Can anyone help me. Why is the Label "Current" NOT left aligned in Panel/Frame? public static void main(String[] args) { JFrame TFrame = new JFrame("Test DisplayLayout"); TFrame.setResizable(true); TFrame.setSize(new Dimension(900, 840)); TFrame.setLocationRelativeTo(null); TFrame.setTitle("DisplayLayout"); TFrame.setVisible(true); JPanel P = DisplayLayout2(); P.setVisible(true); P.setOpaque(true); P.setLayout(new BoxLayout(P, BoxLayout.Y_AXIS)); TFrame.add(P); TFrame.revalidate(); TFrame.repaint(); } public static JPanel DisplayLayout2() { JPanel Panel=new JPanel(); Panel.setVisible(true); Panel.setOpaque(true); Panel.setLayout(new BoxLayout(Panel, BoxLayout.Y_AXIS)); Panel.setAlignmentX(Component.LEFT_ALIGNMENT); JLabel lab = new JLabel("Current"); lab.setHorizontalAlignment(SwingConstants.LEFT); lab.setForeground(Color.WHITE); lab.setBackground(Color.PINK); lab.setOpaque(true); Panel.add(lab,Component.LEFT_ALIGNMENT); JPanel posPanel = new JPanel(); JScrollPane scrollPane = new JScrollPane(posPanel,JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,JScrollPane.HORIZONTAL_SCROLLBAR_NEVER); scrollPane.setPreferredSize(new Dimension(290, 200)); scrollPane.setOpaque(true); posPanel.setBackground(Color.YELLOW); posPanel.setPreferredSize(new Dimension(290, 200)); posPanel.setLayout(new BoxLayout(posPanel, BoxLayout.Y_AXIS)); posPanel.setAlignmentX(Component.LEFT_ALIGNMENT); Panel.add(scrollPane); return Panel; }

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  • Getting the 'external' IP address in Java

    - by Caylem
    Hi I'm not too sure how to go about getting the external IP address of the machine as a computer outside of a network would see it. My following IPAddress class only gets the local IP address of the machine. Any help would be appreciated. Thanks. public class IPAddress { private InetAddress thisIp; private String thisIpAddress; private void setIpAdd(){ try{ InetAddress thisIp = InetAddress.getLocalHost(); thisIpAddress = thisIp.getHostAddress().toString(); } catch(Exception e){} } protected String getIpAddress(){ setIpAdd(); return thisIpAddress; } }

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  • using Inheritence with GUI (graphical user interfaces) in Java

    - by maya
    hi everyone, I work on inheritence with GUI (graphical user interfaces) let me explain for example I made super class which is vehicle and the subclass is car, so the code to make inheritence will be public class Car extends Vehicle then I want to build the class Car as JFrame like public class Car JFrame implements ActionListener { so the problem is that I couldn't put both codes in the same class, and I need to do that. anyone help me. thanks in advance I wish that the question would be clear

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  • Joining remote paths in Java

    - by Mickael Marrache
    I'm using the FTP library provided by Apache (commons-net). I want to check if a file exists on the FTP server so I use the listFiles method of FTPClient: ftpClient.listFiles(remoteFileDir + "\\" + fileName); The current directory is the FTP server root directory. So, the value of remoteFileDir is a path relative to this root directory. My question concerns the merge between the remote directory path and the file name. What is the right way to do it? For a local file, I would do: File file = new File(remoteFileDir,fileName); but here it doesn't work since when I call file.getAbsolutePath(), I get an absolute path for the file in the local current directory which is not what I want. Also, I guess the merging has been done according to my local environment. PS: I looked at How are paths determined on a remote machines? but it doesn't help me. Thanks

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  • Modifying annotation attribute value at runtime in java

    - by Lici
    Hi folks: some methods in our model pojos have been annotated like this: @Column(name="cli_clipping_id", updatable=false, columnDefinition = "varchar(" + ModelUtils.ID_LENGTH + ") COLLATE utf8_bin") columnDefinition attribute is database vendor dependant, so when trying to drop schema in HSQLDB using Hibernate it fails: [ERROR] 16 jun 12:58:42.480 PM main [org.hibernate.tool.hbm2ddl.SchemaExport] Unexpected token: COLLATE in statement [create table cms.edi_editorial_obj (edi_uuid varchar(23) COLLATE ] To fix this, i'm thinking on this solution (but don't want to spend time if it isn't possible) , at runtime, for each method column annotated: Get @Column annotation Create a copy of the column annotation, setting columnDefinition null using javaassist. set column method annotation to the copy column annotation object overriding the old one (i don't know it this is possible) Is it possible to "hack" these methods this way? Any help would be much appreciated ...

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  • java servlet: generate zip file from BLOBs

    - by Zack
    I'm trying to zip a large number of pdf files (stored as BLOBs in the DB) and then return the zip as an attachment to the user. What's the best way to do this without running into memory issues? Another note: I actually need to merge some PDFs prior to adding them to the ZipOutputStream. Therefore, a couple PDFs will need to be stored in memory at a time. I assume it would be best to then store them as temporary files on the server before zipping them all?

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  • Using java class HttpsURLConnection

    - by KB22
    Hi all, I have a small piece of code which basically impements a HTTP-Client, i.e. it POSTS request and works with re RESPONSE. As long as HTTP is concenerned everthing work well. For some reason I now have to support HTTPS too. So here is briefly what I do in order to get a connection opened: URL url = new URL(serverAddress); HttpsURLConnection httpsConn = (HttpsURLConnection) url.openConnection(); This fails, stating: sun.net.www.protocol.https.HttpsURLConnectionImpl cannot be cast to com.sun.net.ssl.HttpsURLConnection I guess this is kinda trivial, but I just don't get what I'm doing wrong in this one... Googled it, and the code just looks right - not? any ideas are appreciated! thanks, K

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  • Trying to convert a 2D image into 3D objects in Java

    - by Kyle
    Hey, I'm trying to take a simple image, something like a black background with colored blocks representing walls. I'm trying to figure out how to go about starting on something like this. Do I need to parse the image and look at each pixel or is there an easier way to do it? I'm using Java3D but it doesn't seem to have any sort of built in support for that...

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  • java: retrieving the "canonical value" from a Set<T> where T has a custom equals()

    - by Jason S
    I have a class Foo which overrides equals() and hashCode() properly. I would like to also would like to use a HashSet<Foo> to keep track of "canonical values" e.g. I have a class that I would like to write like this, so that if I have two separate objects that are equivalent I can coalesce them into references to the same object: class Canonicalizer<T> { final private Set<T> values = new HashSet<T>(); public T findCanonicalValue(T value) { T canonical = this.values.get(value); if (canonical == null) { // not in the set, so put it there for the future this.values.add(value); return value; } else { return canonical; } } } except that Set doesn't have a "get" method that would return the actual value stored in the set, just the "contains" method that returns true or false. (I guess that it assumes that if you have an object that is equal to a separate object in the set, you don't need to retrieve the one in the set) Is there a convenient way to do this? The only other thing I can think of is to use a map and a list: class Canonicalizer<T> { // warning: neglects concurrency issues final private Map<T, Integer> valueIndex = new HashMap<T, Integer>(); final private List<T> values = new ArrayList<T>(); public T findCanonicalValue(T value) { Integer i = this.valueIndex.get(value); if (i == null) { // not in the set, so put it there for the future i = this.values.size(); this.values.add(value); this.valueIndex.put(value, i); return value; } else { // in the set return this.values.get(i); } } }

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  • quick java question

    - by j-unit-122
    private static char[] quicksort (char[] array , int left , int right) { if (left < right) { int p = partition(array , left, right); quicksort(array, left, p - 1 ); quicksort(array, p + 1 , right); } for (char i : array) System.out.print(i + ” ”); System.out.println(); return array; } private static int partition(char[] a, int left, int right) { char p = a[left]; int l = left + 1, r = right; while (l < r) { while (l < right && a[l] < p) l++; while (r > left && a[r] >= p) r--; if (l < r) { char temp = a[l]; a[l] = a[r]; a[r] = temp; } } a[left] = a[r]; a[r] = p; return r; } } hi guys just a quick question regarding the above coding, i know that the above coding returns the following B I G C O M P U T E R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M O P T U R B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U when the sequence BIGCOMPUTER is used but my question is can someone explain to me what is happening in the code and how? i know abit about the quick-sort algorithm but it doesnt seem to be the same in the above example.

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  • Enumeration classes in Java

    - by Crystal
    I have one class that declares an enumeration type as: public enum HOME_LOAN_TERMS {FIFTEEN_YEAR, THIRTY_YEAR}; Is this type usable in another class? I'm basically trying to complete a homework assignment where we have two types of loans, and one loanManager class. When I try to use the HOME_LOAN_TERMS.THIRTY_YEAR in my loanManager class that does not extend or implement the loan class, I get an error saying it 'cannot find symbol HOME_LOAN_TERMS.' So I did not know if my loanManager class needed to implement the two different loan classes. Thanks.

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  • Better way to write this Java code?

    - by Macha
    public void handleParsedCommand(String[] commandArr) { if(commandArr[0].equalsIgnoreCase("message")) { int target = Integer.parseInt(commandArr[1]); String message = commandArr[2]; MachatServer.sendMessage(target, this.conId, message); } else if(commandArr[0].equalsIgnoreCase("quit")) { // Tell the server to disconnect us. MachatServer.disconnect(conId); } else if(commandArr[0].equalsIgnoreCase("confirmconnect")) { // Blah blah and so on for another 10 types of command } else { try { out.write("Unknown: " + commandArr[0] + "\n"); } catch (IOException e) { System.out.println("Failed output warning of unknown command."); } } } I have this part of my server code for handling the types of messages. Each message contains the type in commandArr[0] and the parameters in the rest of commandArr[]. However, this current code, while working seems very unelegant. Is there a better way to handle it? (To the best of my knowledge, String values can't be used in switch statements, and even then, a switch statement would only be a small improvement.

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  • Java Application/Thread Server

    - by Manrico Corazzi
    I am looking for something very close to an application server with these features: it should handle a series of threads/daemons, allowing the user to start-stop-reload each one without affecting the others it should keep libraries separated between different threads/daemons it should allow to share some libraries Currently we have some legacy code reinventing the wheel... and not a perflectly round-shaped one at that! I thought to use Tomcat, but I don't need a web server, except maybe for the simple backoffice user interface (/manager/html). Any suggestion? Is there a non-web application server, or is there a better alternative to Tomcat (more lightweight, for example, or easier to configure)? Thanks in advance.

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  • Java - Calling all methods of a class

    - by Thomas Eschemann
    I'm currently working on an application that has to render several Freemarker templates. So far I have a Generator class that handles the rendering. The class looks more or less like this: public class Generator { public static void generate(…) { renderTemplate1(); renderTemplate2(); renderTemplate3(); } private static void render(…) { // renders the template } private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; … } This works, but it doesn't really feel right. What I would like to do is create a class that holds all the renderTemplate...() methods and then call them dynamically from my Generator class. This would make it cleaner and easier to extend. I was thinking about using something like reflection, but it doesn't really feel like a good solution either. Any idea on how to implement this properly ?

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  • HELP easy java program [closed]

    - by gentrit
    type first integer , type second integer, , program repeatedly outputs the second value of the number of times indicated by the first value. Example use inputs 4 and 2, 222 2 displayed. another example user inputs 3 and 8 , 88 8 displayed

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  • base-n series generator for a given number in java,,

    - by Senthil
    I want to create a program for generating the series for the given base-n. , for example if my input is 2,then series shuould be, 00,01,10,11,etc.,(binary) if my input is 10,then series shuould be,1,2,3,4,5,etc.,(decimal) is there any general mechanism to find these numbers so that I can program for base-n.,

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  • Get annotations of return type in Java

    - by Apropos
    I'm using Spring MVC and am using aspects to advise my controllers. I'm running into one issue: controllers that return a value annotated with the @ResponseBody type. How are you able to find the annotations applied to the return type? @Around("myPointcut()") private Object checkAnnotations(ProceedingJoinPoint pjp) throws Throwable { Object result = pjp.proceed(); Method method = ((MethodSignature)pjp.getSignature()).getMethod(); System.out.println("Checking return type annotations."); for(Annotation annotation : method.getReturnType().getAnnotations()){ System.out.println(annotation.toString()); } System.out.println("Checking annotations on returned object."); for(Annotation annotation : result.getClass().getAnnotations()){ System.out.println(annotation.toString()); } return result; } Unfortunately, neither of these methods seem to have the desired effect. I can retrieve annotations on the type of object being returned, but not the ones being added at return time.

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  • Java simple data format british time

    - by DD
    Hi, I am using simple date format to allow users to specify which time zone they are sending data in: DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss,z"); This works fine: e.g. df.parse("2009-05-16 11:07:41,GMT"); However, if someone is always sending time in London time (i.e. taking into account daylight savings), what would be the approriate time zone String to add? e.g. this doesnt work: df.parse("2009-05-16 11:07:41,Europe/London"); Thanks.

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  • Incorrect Date in Java

    - by Polaris
    I use next code to print current time Calendar cal = Calendar.getInstance(); System.out.println(cal.getTime()); I have Windows XP sp3 istalled. Current time in system tray is 14:30. But this code return 13:30 Why returned time is wrong?

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