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  • Implementing clone on a LinkedList

    - by devoured elysium
    I am trying to implement a clone() method on a DoubleLinkedList. Now, the problem is that implementing it by "the convention" is a lot more troublesome than just creating a new DoubleLinkedList and filling it with all the elements of my current DoubleLinkedList. Is there any inconvenient I am not seeing when doing that? Here is my current approach: @Override public DoubleLinkedList<T> clone() { DoubleLinkedList<T> dll = new DoubleLinkedList<T>(); for (T element : dll) { dll.add(element); } return dll; } Here is what it would be by the convention: @Override public DoubleLinkedList<T> clone() { try { DoubleLinkedList<T> dll = (DoubleLinkedList<T>)super.clone(); //kinda complex code to copy elements return dll; } catch (CloneNotSupportedException e) { throw new InternalError(e.toString()); } }

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  • Compare class objects

    - by reto
    I have to compare a class object against a list of pre defined classes. Is it safe to use == or should I use equals()? if (klass == KlassA.class) { } else if (klass == KlassB.class) { } else if (klass == KlassC.class) { } else { } Note: I cannot use instanceof, I don't have an object, I just have the class object. I (mis)use it like an enum in this situation! Thanks!

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  • Use the serialVersionUID or suppress warnings?

    - by Okami
    Dear all, first thing to note is the serialVersionUID of a class implementing Interface Serializable is not in question. What if we create a class that for example extends HttpServlet? It also should have a serialVersionUID. If someone knows that this object will never be serialized should he define it or add an annotation to suppress those warnings? What would you do and why? Thanks for sharing your thoughts. Okami

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  • Implementing Unowned relationship Google App Engine

    - by nwallman
    My question is more of a best practices question on how to implement unowned relationships with Google App Engine. I am using JDO to do my persistence and like recommended in the google docs I'm persisting my list of unowned relationships like so: @PersistenceCapable(identityType = IdentityType.APPLICATION) public class User implements Serializable, UserDetails { ... @Persistent private List<Key> groups; ... } Now I came across my predicament when I went to query that list of objects using they Key object. So when I get my list of group keys in order to actually return a list of Group objects I have to do a look up on that key to get the object. My question is what is the recommended way of doing a unowned look up on a model object? Should I have an instance of the PersistanceManagerFactory on my Model object so I can do a lookup? Should I have an instance of my GroupDAO object on my Model object so I can do a look up? Should I have a Utility to do this type of lookup? I'm new to this so I just want to know which is the best way to do this. Thanks.

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  • Write to text file using ArrayList

    - by Ugochukwutubelum Chiemenam
    The program is basically about reading from a text file, storing the current data into an ArrayList, then writing data (from user input) into the same text file. Kindly let me know where I am going wrong in this sub-part? The data inside the text file is as follows: abc t1 1900 xyz t2 1700 The compiler is showing an error at the line output.format("%s%s%s%n", public class justTesting { private Scanner input; private Formatter output; private ArrayList<Student> tk = new ArrayList<Student>(); public static void main(String[] args) { justTesting app = new justTesting(); app.create(); app.writeToFile(); } public void create() { Text entry = new Text(); Scanner input = new Scanner(System.in); System.out.printf("%s\n", "Please enter your name, ID, and year: "); while (input.hasNext()) { try { entry.setName(input.next()); entry.setTelNumber(input.next()); entry.setDOB(input.next()); for (int i = 0; i < tk.size(); i++) { output.format("%s%s%s%n", tk.get(i).getName(), tk.get(i) .getTelNumber(), tk.get(i).getDOB()); } } catch (FormatterClosedException fce) { System.err.println("Error writing to file."); return; } catch (NoSuchElementException nsee) { System.err.println("Invalid input. Try again: "); input.nextLine(); } System.out.printf("%s\n", "Please enter your name, ID, and year: "); } } public void writeToFile() { try { output = new Formatter("testing.txt"); } catch (SecurityException se) { System.err .println("You do not have write access permission to this file."); System.exit(1); } catch (FileNotFoundException fnfe) { System.err.println("Error opening or creating file."); System.exit(1); } } }

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  • Eclipse "Add unimplemented methods" method ordering

    - by Steve Kuo
    Eclipse has a feature "Add unimplemented methods" that adds the unimplemented methods for a class (such as when implementing an interface). When Eclipse adds the methods it adds them in alphabetical order. Is there a way to configure Eclipse to add them in the order that they appear in the interface (or abstract class)?

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  • JPA and aggregate functions. How do I use the result of the query?

    - by Bogdan
    Hey guys, I'm new to ORM stuff and I need some help understanding something. Let's assume I have the following standard SQL query: SELECT *, COUNT(test.testId) AS noTests FROM inspection LEFT JOIN test ON inspection.inspId = test.inspId GROUP BY inspection.inspId which I want to use in JPA. I have an Inspection entity with a one-to-many relationship to a Test entity. (an inspection has many tests) I tried writing this in JPQL: Query query = em.createQuery("SELECT insp, COUNT(???what???) FROM Inspection insp LEFT JOIN insp.testList " + "GROUP BY insp.inspId"); 1) How do I write the COUNT clause? I'd have to apply count to elements from the test table but testList is a collection, so I can't do smth like COUNT(insp.testList.testId) 2) Assuming 1 is resolved, what type of object will be returned. It will definitely not be an Inspection object... How do I use the result?

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  • Design pattern: polymorphisim for list of objects

    - by ziang
    Suppose I have a class A, and A1, A2 inherits from A. There are 2 functions: List<A1> getListA1(){...} List<A2> getListA2(){...} Now I want to do something similar to both A1 and A2 in another function public void process(List<A>){...} If I want to pass the instance of either ListA1 or ListA2, of course the types doesn't match because the compiler doesn't allow the coercion from List< A1 to List< A. I can't do something like this: List<A1> listA1 = getListA1(); List<A> newList = (List<A>)listA1; //this is not allowed. So what is the best approach to the process()? Is there any way to do it in a universal way rather than write the similar code to both List and List?

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  • JSF h:outputStylesheet doesn't work everywhere

    - by s3rius
    I'm currently learning Icefaces, now I'm trying to integrate a css file via h:OutputStylesheet into my code. I have a main page and a second page. Using outputStylesheet in my main page works well (and then I can also access the css in the second page, which I guess is intended). But when I try to integrate it in my second page it doesn't work at all. The code for both pages is basically identical. main page: <h:head></h:head> <h:body> <!-- this line works --> <h:outputStylesheet library="css" name="style.css" /> <!-- this line is only shown in red if the outputStylesheet from above is there --> <div class="red">This is red color in main page</div> </h:body> second page: <h:head></h:head> <h:body> <!-- this line doesn't work --> <h:outputStylesheet library="css" name="style.css" /> <!-- this line is only shown in red if the outputStylesheet in main page is there --> <div class="red">This is red color in second page</div> </h:body> I've made sure that I have h:body and h:head tags in both files. There's nothing more in the html pages except the standard doctype and xml version declarations. I've tried packing everything into h:forms, but that doesn't change anything. Can anyone explain to me what's going on?

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  • How to view my Android app created database, via my android app?

    - by suufang
    I'm creating an application that collects users location (Cell broadcast location code) and saves that location with a name of users option, for example say my CB location code is 546034, now my app allows me to store that location code with a name of my choice say 'Home'. So, essentially my app has that following modules, To collect users CB location. To collect a custom name from user of that location. To store these values in a database. I've succeeded in doing all the above modules. I have a sub-module for my third module which has an option for user, of showing and deleting the database values, the screen shot looks as follows, Now, Users should be able to view and delete entries when he chooses the option 'View my database of locations' I've learned how to query my database values and I'm stuck with creating a list view and providing the delete option. My code for getting the database values and querying values goes as follows, submit.setOnClickListener(new View.OnClickListener() { public void onClick(View arg0) { String locname = name.getText().toString(); if(locname.length()==0) { Toast.makeText(getBaseContext(), "Please enter the location name, for example 'Home'.", Toast.LENGTH_LONG).show(); } else { SQLiteDatabase cd = openOrCreateDatabase("mydata", MODE_WORLD_READABLE, null); cd.execSQL("CREATE TABLE IF NOT EXISTS MLITable (CblocationCode INT(10), CblocationName VARCHAR);"); cd.execSQL("INSERT INTO MLITable VALUES ('"+str+ "','"+locname+ "');"); cd.close(); Toast.makeText(getBaseContext(), "value successfully entered.", Toast.LENGTH_LONG).show(); } } }); viewdb.setOnClickListener(new View.OnClickListener() { public void onClick(View arg0) { // here comes the code for viewing the database and deleting SQLiteDatabase db = openOrCreateDatabase("mydata", MODE_WORLD_READABLE, null); Cursor c = db.rawQuery("SELECT * FROM MLITble", null); db.close(); } }); I can see that I've read the table values, but I'm not able to create a display for those values. Help required. Thank you.

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  • FindBugs and CheckForNull on classes vs. interfaces

    - by ndn
    Is there any way to let FindBugs check and warn me if a CheckForNull annotation is present on the implementation of a method in a class, but not on the declaration of the method in the interface? import javax.annotation.CheckForNull; interface Foo { public String getBar(); } class FooImpl implements Foo { @CheckForNull @Override public String getBar() { return null; } } public class FindBugsDemo { public static void main(String[] args) { Foo foo = new FooImpl(); System.out.println(foo.getBar().length()); } } I just discovered a bug in my application due to a missing null check that was not spotted by FindBugs because CheckForNull was only present on FooImpl, but not on Foo, and I don't want to spot all other locations of this problem manually.

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  • Cache JSP based on URL parameter

    - by Satheesh
    I have a jsp file pageshow.jsp and the parameter id, Is there any way to cache the jsp file in server-side based on the url parameter Requesting page pageshow.jsp?id=100 get from cache instead of building from server Requesting page pageshow.jsp?id=200 get from cache instead of building from server Above two pages should have different cache content since their parameter are different This may avoid the rebuilding the jsp file in server side and also decrease the server load

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  • Tuning garbage collections for low latency

    - by elec
    I'm looking for arguments as to how best to size the young generation (with respect to the old generation) in an environment where low latency is critical. My own testing tends to show that latency is lowest when the young generation is fairly large (eg. -XX:NewRatio <3), however I cannot reconcile this with the intuition that the larger the young generation the more time it should take to garbage collect. The application runs on linux, jdk 6 before update 14, i.e G1 not available.

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  • a problem with JTabedPanel

    - by sirvan
    hi, I have an application that includes an JtabedPanel and two Tabes with some componetnts,my problem is when i click on another Tab,it's components not appeared immediately but when mouse courser move over each component(Jcheckbox,Jbutton and so on) of the tab,the components will appear but not correctly (see below image) This is my CODE . . .

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  • Remove leading zero's from alphanumeic text

    - by cedar715
    I've seen questions to prefix zeros here in SO. But not the other way !! Can you guys suggest me how to remove the leading zeros in alphanumeric text. Are there any built-in APIs or do I need to write a method to trim the leading zero's? Example: 01234 converts to 1234 0001234a converts to 1234a 001234-a converts to 1234-a 101234 remains as 101234 2509398 remains as 2509398 123z remains as 123z 000002829839 converts to 2829839

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  • Connection Pooling in J2SE?

    - by Zombies
    It is hard to find a resource on this without finding J2EE, but here is what I am looking for: All I have is a standard J2SE app, it makes a lot of DB connections. I simply need to make use of a connection pool. Any suggestions?

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