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• Write a tree class in Java where each level has a unique object type

  - by user479576

  I need to write a tree class in Java where each level has a unique object type. The way it is written below does not take advantage of generics and causes alot of duplicate code. Is there a way to write this with Generics ? public class NodeB { private String nodeValue; //private List<NodeB> childNodes; // constructors // getters/setters } public class NodeA { private String value; private List<NodeB> childNodes; // constructors // getters/setters } public class Tree { private String value; private List<NodeA> childNodes; // constructors // tree methods }

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• java - reduce external jar file size

  - by joe_shmoe

  Hi all, still learning, so be patient :) I've developed a module for a Java project. The module depends on external library (fastutil). the problem is, the fastutil.jar file is a couple of times heavier than the whole project itself (14 MB). I only use a tiny subset of the classes from the library. the module is now finished, and no-one is likely to extend it in future. is there a way I could extract only the relevant class to some fastutil_small.jar so that others don't have to download all this extra weight? there's probably a simple answer to this, but as I said, I still consider myself a noob. Thanks a lot

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• Java spliting strings

  - by N0b

  Hi I've got a Java problem. I'm trying split a string when ever a " " occurs, for example the sentence test abc. Then move the first letter in each word from first to last. I got the moving the letter to work on the original string using String text = JOptionPane.showInputDialog(null,"Skriv in en normal text:"); char firstLetter = text.charAt(0); normal = text.substring(1,text.length()+0) + firstLetter; So my question is how would I split the string then start moving the letters around in each part of the cut string? Thanks in advance

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• Java Pack No Resize

  - by ikurtz

  i am learning Java at the moment and have the following question: i am adding my controls to JFrame and then pack() before displaying. this runs the application and all is very nice. i was wondering is there a way to stop the user from resizing the application window? also is there a way to for the image in JLabel to expand as the user changes the application window? at the moment i have it as: constraints.fill = GridBagConstraints.BOTH; constraints.anchor = GridBagConstraints.CENTER; and it only centers the image, i would like to be able to expand/shrink the image. thanks.

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• The right way to implement communication between java objects

  - by imoschak

  I'm working on an academic project which simulates a rather large queuing procedure in java. The core of the simulator rests within one package where there exist 8 classes each one implementing a single concept. Every class in the project follows SRP. These classes encapsulate the behavior of the simulator and inter-connect every other class in the project. The problem that I has arisen is that most of these 8 classes are, as is logical i think, tightly coupled and each one has to have working knowledge of every other class in this package in order to be able to call methods from it when needed. The application needs only one instance of each class so it might be better to create static fields for each class in a new class and use that to make calls -instead of preserving a reference in each class for every other class in the package (which I'm certain that is incorrect)-, but is this considered a correct design solution? or is there a design pattern maybe that better suits my needs?

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• Running interrelated methods continously using java

  - by snehalata

  I have written application which downloads data from a website every 10 mins and writes to a file.Then these files are merged into one file and then R program is run on this merged file to perform sentiment analysis and result is stored in hbase. I want the process of merging files,running R and then storing to HBase to run continuosly on the downloaded data. For running R,we are running R script from java program.We have used Runtime.getRuntime().exec() method to run R program but it doesn't wait for R program to complete and method in the next line starts executing.Using p.waitFor() did not help . What approach should I use to do merge then run R and finally store results in Hbase?Should I use timer class??

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• String comparison in Java

  - by Kliver Max

  I want to compare two strings using Java. First sting name i get from .mif file using GDAL in cp1251 encoding. Second kadname i get from jsp. To compare i do this: if (attrValue instanceof String) { String string3 = new String((attrValue.toString()).getBytes("ISO-8859-1"), "cp1251"); dbFeature.setAttribute(name, string3); System.out.println("Name=" + name); System.out.println("kadname=" + kadname); if (name.equalsIgnoreCase(kadname)) { kadnum = string3; System.out.println("string3" + string3); } } And in console i get this: Name = kadnumm kadname = kadnumm Whats wrong with this?

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• Operation Problems in Java Generic

  - by alantheweasel

  I got some problem when i was learning Java Generic : interface calculator<T, R> { public void execute(T t, R r); } class executeAdd<T, R> implements calculator<T, R> { private T first; private R second; public executeAdd(T first, R second) { super(); this.first = first; this.second = second; } @Override public void execute(T t, R r) { // TODO Auto-generated method stub Object o = t + r // ERROR ! What i could do it ? } }

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• Drawing graphs on java

  - by nunos

  I want to draw graphs (nodes and edges) in Java. However, since I don't know how to go about it, I would like to have some advice before starting. How should I do this? use Graphics2D package, right? How about the labels for the nodes? should I use something like drawString and handle all the "centering" manually or create a JLabel for that? Can I put a JLabel on a Graphics2D environment? I have searched but haven't found any simple implementation of this. If you know of one, please provide the link in your answer. Thanks.

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• Simple Java library for storing statistical observations and calculating statistics such as stddev,

  - by knorv

  For logging purposes I want to collect the response times of an external system, and periodically fetch various statistics (such as min/max/stddev) of the response times. I'm looking for a pure in-memory solution. What Java library can help me with this simple task? I'm looking for an API that would ideally look something along the lines of: StatisticsCollector s = new StatisticsCollector(); while (...) { double responseTime = ...; s.addObservation(responseTime); } double stddev = s.getStandardDeviation(); double mean = s.getMean();

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• Java swing center JDialog over parent

  - by Chris Drappier

  I have a Java swing application with a button that produces a popup window when a certain action is performed. I'd like to align the center point of the popup window with the center point of the parent window when it is rendered. How can I calculate the x,y coordinates to plug into setLocation() for the popup window? EDIT: just to clarify. I do not want the behavior of setLocationRelativeTo() because that sets the top-left pixel of the popup over the center pixel of the parent frame. I want to set the center pixel of the popup over the center pixel of the parent frame. Also, I'm not interested in whether or not a popup window is good practice. I'm past that now. thanks

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• Java deserialization speed

  - by celicni

  I am writing a Java application that among other things needs to read a dictionary text file (each line is one word) and store it in a HashSet. Each time I start the application this same file is being read all over again (6 Megabytes unicode file). That seemed expensive, so I decided to serialize resulting HashSet and store it to a binary file. I expected my application to run faster after this. Instead it got slower: from ~2,5 seconds before to ~5 seconds after serialization. Is this expected result? I thought that in similar cases serialization should increase speed.

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• Java exception translations

  - by user3079275

  Apologies if this has been discussed on other threads but I find it helps clarify my thinking when I am forced to write down my questions. I am trying to properly understand the concept of checked vs unchecked exceptions and exception translation in Java but I am getting confused. So far I understood that checked exceptions are exceptions that need to be always caught in a try/catch block otherwise I get a compile time error. This is to force programmers to think about abnormal situations that might happen at run time (like disk full etc). Is this right? What I did not get was why we have unchecked exceptions, when are they useful? Is it only during development time to debug code that might access an illegal array index etc? This confusion is because I see that Error exceptions are also unchecked as is RunTimeException but its not clear to me why they are both lumped together into an unchecked category?

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• how to generate XML (in String representation) in java

  - by flyingfromchina

  I have defined a java class, but only need to output some of the fields of this class into an XML. The returned type must be a String. I first opted for the easiest way using a StringBuffer. However, when I tried to process the output String represenation, it failed. I think it is mostly likely because there are some characters that are not encoded in the UTF-8 in the input. Could someone tell me what is the best way to handle this? Thanks.

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• Debugging in netbeans (java)

  - by Daen

  I have been asking this myself for a while. Debugging in visual studio goes smooth. But when i debugg in Netbeans(java) i find myself more then half of the time browsing trough the system code itself. This makes it almost unpossible for me to detect hard to find bugs, cause debugging simply is to tedious and unmanageable. How can this be avoided? Stepping out all the time takes a insane amount of time, and i only wish to debug the code i have written down. I usally add all the controls myself without using any drag and drop for forms if that makes any difference in the total picture. Regards.

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• cron library for java

  - by nutsiepully

  I am looking for a cron expression library in java. Something that can parse cron expressions and return me future fire times for the trigger. API on the lines of. CronExpression cronExpression = new CronExpression("0 30 4 * * *"); List<Date> fireTimes = cronExpression.getFireTimes(todaysDate, nextWeekDate); I don't want to use something as complicated as quartz. The purpose is to basically use cron like a regex for timings. That's all. I do not want a background scheduler. I tried googling but wasn't able to find anything very helpful. Any suggestions would be appreciated. Regards, Pulkit P.S - I looked at using the CronExpression class out of quartz. Wasn't very helpful - failing some tests.

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• How do I make a OnClickListener in Java

  - by Bob

  I used to program with html and to make a alert all I had to do was make an alert("Hello World"); but with java it is much more advanced. I need help to make a button that when someone clicks it, it has an alert message on the screen. This is my code right now: MyOnClickListener onClickListener = new MyOnClickListener() { @Override public void onClick(View v) { Intent returnIntent = new Intent(); returnIntent.putExtra("deleteAtIndex",idx); setResult(RESULT_OK, returnIntent); finish(); } }; for (int i =0;i<buttonList.size();i++) { buttonList.get(i).setText("Remove"); buttonList.get(i).setOnClickListener(onClickListener); }

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• Defining Proper Classes with Java

  - by user2579706

  Ok, I'm studying Java and have the following question: "Assume you defined a class named MyClass. A student wants to use your class and tries to declare an instance named myObj and instantiate it. He tried the following: MyObj MyClass = new MyClass( ); Why won't his code work? Show how he should correct it. " I'm not sure how to do this? Can anyone point me in the right direction? Many thanks.

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• Java, UnmarshallingException caused by XML attribute with special chars: ;ìè+òàù-<^èç°§_>!£$%&/()=?~

  - by segolas

  Hi, my xml file has a tag with an attribute "containsValue" which contains the "special" characters you can see in the subject: <original_msg_body id="msgBodySpecialCharsRule" containsValue=";ìè+òàù-<^èç°§_>!£$%&/()=?~`'#;" /> in my xml schema the attribute has xs:string: <xs:attribute name="containsValue" type="xs:string" /> I use this value inside a Java software which check if this value is contained inside another String. but I always obtain this Exception: javax.xml.bind.UnmarshalException - with linked exception: [org.xml.sax.SAXParseException: The value of attribute "containsValue" associated with an element type "original_msg_body" must not contain the '<' character.] How can I solve it? I've tried changing the attribute type to xs:NMTOKEN, ut I get the same exception. Is there any other type? I think I could change the characters encoding, for example using the HTML representation, like <, but than could be tricky for the string comparison...

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• Managing User & Role Security with Oracle SQL Developer

  - by thatjeffsmith

  With the advent of SQL Developer v3.0, users have had access to some powerful database administration features. Version 3.1 introduced more powerful features such as an interface to Data Pump and RMAN. Today I want to talk about some very simple but frequently ran tasks that SQL Developer can assist with, like: identifying privs granted to users managing role privs assigning new roles and privs to users & roles Before getting started, you’ll need a connection to the database with the proper privileges. The common ROLE used to accomplish this is the ‘DBA‘ role. Curious as to what the DBA role is actually comprised of? Let’s find out! Open the DBA Console First make sure you’re connected to the database you want to manage security on with a privileged administrator account. Then open the View menu and select ‘DBA.’ Accessing the DBA panel ‘Create’ a Connection Click on the green ‘+’ button in the DBA panel. It will ask you to choose a previously defined SQL Developer connection. Defining a DBA connection in Oracle SQL Developer Once connected you will see a tree list of DBA features you can start interacting with. Expand the ‘Security’ Tree Node As you click on an object in the DBA panel, the ‘viewer’ will open on the right-hand-side, just like you are accustomed to seeing when clicking on a table or stored procedure. Accessing the DBA role If I’m a newly hired Oracle DBA, the first thing I might want to do is become very familiar with the DBA role. People will be asking you to grant them this role or a subset of its privileges. Once you see what the role can do, you will become VERY protective of it. My favorite 3-letter 4-letter word is ‘ANY’ and the DBA role is littered with privileges like this: ANY TABLE privs granted to DBA role So if this doesn’t freak you out, then maybe you should re-consider your career path. Or in other words, don’t be granting this role to ANYONE you don’t completely trust to take care of your database. If I’m just assigned a new database to manage, the first thing I might want to look at is just WHO has been assigned the DBA role. SQL Developer makes this easy to ascertain, just click on the ‘User Grantees’ panel. Who has the keys to your car? Making Changes to Roles and Users If you mouse-right-click on a user in the Tree, you can do individual tasks like grant a sys priv or expire an account. But, you can also use the ‘Edit User’ dialog to do a lot of work in one pass. As you click through options in these dialogs, it will build the ‘ALTER USER’ script in the SQL panel, which can then be executed or copied to the worksheet or to your .SQL file to be ran at your discretion. A Few Clicks vs a Lot of Typing These dialogs won’t make you a DBA, but if you’re pressed for time and you’re already in SQL Developer, they can sure help you make up for lost time in just a few clicks!

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• How to structure applications as multiple projects an name the packages in Java

  - by lostiniceland

  Hello Everyone I would like to know how you set up your projects in Java For example, in my current work-project, a six year old J2EE app with approximately 2 million LoC, we only have one project in Eclipse. The package structure is split into tiers and then domains, so it follows guidelines from Sun/Oracle. A huge ant-script is building different jars out of this one source-folder Personally I think it would be better to have multiple projects, at least for each tier. Recently I was playing around with a projects-structure like this: Domainproject (contains only annotated pojos, needed by all other projects) Datalayer (only persistence) Businesslogic (services) Presenter View This way, it should be easier to exchange components and when using a build tool like Maven I can have everything in a repository so when only working on the frontend I can get the rest as a dependecy in my classpath. Does this makes sense to you? Do you use different approaches and how do they look like? Furthermore I am struggeling how to name my packages/projects correctly. Right now, the above project-structure reflects in the names of the packages, eg. de.myapp.view and it continues with some technical subfolders like internal or interfaces. What I am missing here, and I dont know how to do this properly, is the distinction to a certain domain. When the project gets bigger it would be nice to recognise a particular domain but also the technical details to navigate more easily within the project. This leads to my second question: how do you name your projects and packages?

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• java GC periodically enters into several full GC cycles

  - by Peter

  Environment: sun JDK 1.6.0_16 vm settings: -XX:+DisableExplicitGC -XX:+UseConcMarkSweepGC -Xms1024 -Xmx1024M -XX:MaxNewSize=448m -XX:NewSize=448m -XX:SurvivorRatio=4(6 also checked) -XX:MaxPermSize=128M OS: windows server 2003 processor: 4 cores of INTEL XEON 5130, 2000 Hz my application description: high intensity of concurrent(java 5 concurrency used) operations completed each time by commit to oracle. it's about 20-30 threads run non stop, doing tasks. application runs in JBOSS web container. My GC starts work normally, I see a lot of small GCs and all that time CPU shows good load, like all 4 cores loaded to 40-50%, CPU graph is stable. Then , after 1 min of good work, CPU starts drop to 0% on 2 cores from 4, it's graph becomes unstable, goes up and down("teeth"). I see, that my threads work slower(I have monitoring), I see that GC starts produce a lot of FULL GC during that time and next 4-5 minutes this situation remains as is, then for short period of time, like 1 minute, it gets back to normal situation, but shortly after that all bad thing repeats. Question: Why I have so frequent full GC??? How to prevent that? I played with SurvivorRatio - does not help. I noticed, that application behaves normally until first FULL GC occurs, while I have enough memory. Then it runs badly. my GC LOG: starts good then long period of FULL GCs(many of them) 1027.861: [GC 942200K-623526K(991232K), 0.0887588 secs] 1029.333: [GC 803279K(991232K), 0.0927470 secs] 1030.551: [GC 967485K-625549K(991232K), 0.0823024 secs] 1030.634: [GC 625957K(991232K), 0.0763656 secs] 1033.126: [GC 969613K-632963K(991232K), 0.0850611 secs] 1033.281: [GC 649899K(991232K), 0.0378358 secs] 1035.910: [GC 813948K(991232K), 0.3540375 secs] 1037.994: [GC 967729K-637198K(991232K), 0.0826042 secs] 1038.435: [GC 710309K(991232K), 0.1370703 secs] 1039.665: [GC 980494K-972462K(991232K), 0.6398589 secs] 1040.306: [Full GC 972462K-619643K(991232K), 3.7780597 secs] 1044.093: [GC 620103K(991232K), 0.0695221 secs] 1047.870: [Full GC 991231K-626514K(991232K), 3.8732457 secs] 1053.739: [GC 942140K(991232K), 0.5410483 secs] 1056.343: [Full GC 991232K-634157K(991232K), 3.9071443 secs] 1061.257: [GC 786274K(991232K), 0.3106603 secs] 1065.229: [Full GC 991232K-641617K(991232K), 3.9565638 secs] 1071.192: [GC 945999K(991232K), 0.5401515 secs] 1073.793: [Full GC 991231K-648045K(991232K), 3.9627814 secs] 1079.754: [GC 936641K(991232K), 0.5321197 secs]

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• StringBufferInputStream Question in Java

  - by JJG

  I want to read an input string and return it as a UTF8 encoded string. SO I found an example on the Oracle/Sun website that used FileInputStream. I didn't want to read a file, but a string, so I changed it to StringBufferInputStream and used the code below. The method parameter jtext, is some Japanese text. Actually this method works great. The question is about the deprecated code. I had to put @SuppressWarnings because StringBufferInputStream is deprecated. I want to know is there a better way to get a string input stream? Is it ok just to leave it as is? I've spent so long trying to fix this problem that I don't want to change anything now I seem to have cracked it. @SuppressWarnings("deprecation") private String readInput(String jtext) { StringBuffer buffer = new StringBuffer(); try { StringBufferInputStream sbis = new StringBufferInputStream (jtext); InputStreamReader isr = new InputStreamReader(sbis, "UTF8"); Reader in = new BufferedReader(isr); int ch; while ((ch = in.read()) > -1) { buffer.append((char)ch); } in.close(); return buffer.toString(); } catch (IOException e) { e.printStackTrace(); return null; } }

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• Generics Java and Shadowing of type parameters

  - by rubixibuc

  This code seems to work fine class Rule<T> { public <T>Rule(T t) { } public <T> void Foo(T t) { } } Does the method type parameter shadow the class type parameter? Also when you create an object does it use the type parameter of the class? example Rule<String> r = new Rule<String>(); Does this normally apply to the type parameter of the class, in the situation where they do not conflict? I mean when only the class has a type parameter, not the constructor, or does this look for a type parameter in the constructor? If they do conflict how does this change? SEE DISCUSSION BELOW if I have a function call x = <Type Parameter>method(); // this is a syntax error even inside the function or class ; I must place a this before it, why is this, and does everything still hold true. Why don't I need to prefix anything for the constructor call. Shouldn't Oracle fix this.

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• Slowing process creation under Java?

  - by oconnor0

  I have a single, large heap (up to 240GB, though in the 20-40GB range for most of this phase of execution) JVM [1] running under Linux [2] on a server with 24 cores. We have tens of thousands of objects that have to be processed by an external executable & then load the data created by those executables back into the JVM. Each executable produces about half a megabyte of data (on disk) that when read right in, after the process finishes, is, of course, larger. Our first implementation was to have each executable handle only a single object. This involved the spawning of twice as many executables as we had objects (since we called a shell script that called the executable). Our CPU utilization would start off high, but not necessarily 100%, and slowly worsen. As we began measuring to see what was happening we noticed that the process creation time [3] continually slows. While starting at sub-second times it would eventually grow to take a minute or more. The actual processing done by the executable usually takes less than 10 seconds. Next we changed the executable to take a list of objects to process in an attempt to reduce the number of processes created. With batch sizes of a few hundred (~1% of our current sample size), the process creation times start out around 2 seconds & grow to around 5-6 seconds. Basically, why is it taking so long to create these processes as execution continues? [1] Oracle JDK 1.6.0_22 [2] Red Hat Enterprise Linux Advanced Platform 5.3, Linux kernel 2.6.18-194.26.1.el5 #1 SMP [3] Creation of the ProcessBuilder object, redirecting the error stream, and starting it.

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