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  • Initialize an object in java

    - by harigm
    Is it the right Way we initialise the the object? I have a class Sample I want to initialise the Object in my Sample1 Class After intialisation I dont require to use the object of Sample Class. In that Case Can I initialise that object as new Sample(); instead of Sample s = new Sample(); if I am not going to use s anywhere in my Sample1 Class My question, is this a good practice to do that? will there be any after affects

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  • Drag and Drop and identify locations with java

    - by out_sider
    I'm trying to do something quite simple, but I'm having a hard time finding good examples on the net to what I want specifically. I'd like to somehing very similer to what it's here: Dao It's a simple game called DAO and I just need to have a background image with 16 squares (4x4) and drag and drop the images (pieces) on each square to the others. I'm developing the interface using swing and I simply want to know a good place to find tutorials for such implementations or a simple suggestion on how to do it. Thanks in advance

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  • Why fill() and copy() of Collections in java is implemented this way

    - by Priyank Doshi
    According to javadoc... Collections.fill() is written as below : public static <T> void fill(List<? super T> list, T obj) { int size = list.size(); if (size < FILL_THRESHOLD || list instanceof RandomAccess) { for (int i=0; i<size; i++) list.set(i, obj); } else { ListIterator<? super T> itr = list.listIterator(); for (int i=0; i<size; i++) { itr.next(); itr.set(obj); } } } Its easy to understand why they didn't use listIterator for if (size < FILL_THRESHOLD || list instanceof RandomAccess) condition as of RandomAccess. But whats the use of size < FILL_THRESHOLD in above? I mean is there any significant performance benefit over using iterator for size>=FILL_THRESHOLD and not for size < FILL_THRESHOLD ? I see the same approach for Collections.copy() also : public static <T> void copy(List<? super T> dest, List<? extends T> src) { int srcSize = src.size(); if (srcSize > dest.size()) throw new IndexOutOfBoundsException("Source does not fit in dest"); if (srcSize < COPY_THRESHOLD || (src instanceof RandomAccess && dest instanceof RandomAccess)) { for (int i=0; i<srcSize; i++) dest.set(i, src.get(i)); } else { ListIterator<? super T> di=dest.listIterator(); ListIterator<? extends T> si=src.listIterator(); for (int i=0; i<srcSize; i++) { di.next(); di.set(si.next()); } } } FYI: private static final int FILL_THRESHOLD = 25; private static final int COPY_THRESHOLD = 10;

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  • Java Multi threading - Avoid duplicate request processing

    - by seawaves
    I have following multi threaded environment scenario - Requests are coming to a method and I want to avoid the duplicate processing of concurrent requests coming. As multiple similar requests might be waiting for being processed in blocked state. I used hashtable to keep track of processed request, but it will create memory leaks, so how should keep track of processed request and avoid the same requests to be processed which may be in blocking state.

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  • What does this java output mean?!

    - by Phil
    public class Arrys { private int[] nums; //Step 3 public Arrys (int arrySize) { nums = new int[arrySize]; } public int [] getNums (){ return nums; } } Test class: public class TestArrys { public static void main(String args[]) { //Step 4 Arrys arry = new Arrys(10); System.out.println("\nStep4 "); for(int index = 0; index < arry.getNums().length; index++) { System.out.print(arry.getNums()); } } } It's incredibly simple, that is why I think I'm doing something fundamentally wrong. All I want is to display the value of the array. This is what I get back. I am totally lost, there is nothing in my book that explains this nor does googling it help. Step4 [I@1ac88440[I@1ac88440[I@1ac88440[I@1ac88440[I@1ac88440[I@1ac88440[I@1ac88440[I@1ac88440[I@1ac88440[I@1ac88440[I@1ac88440

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  • Java interface 'interview'-style problem

    - by Codenotguru
    Problem/Task: Write an interface with one method and two classes that implement this interface. Now write a main method with an array that holds an instance of each class. Using a for-each loop, invoke the method upon each item. Is this an interview question? (I'm not sure if the author meant to post this as a question or was looking for an answer to the above.)

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  • Problem decrementing in Java with '-='

    - by hanesjw
    I'm making a scrolling game on Android and am having a hard time figuring out why the code below does not decrement past 0. Objects start at the end of the screen (so the x position is equal to the width of the screen) the objects move accross the screen by decrementing their x positions. I want them to scroll off of the screen, but when the x position hits 0, the objects just stay at 0, they do not move into the negatives. Here is my code to move objects on the screen private void incrementPositions(long delta) { float incrementor = (delta / 1000F) * Globals.MAP_SECTION_SPEED; for(Map.Entry<Integer, HashMap<Integer, MapSection>> column : scrollingMap.entrySet()) { for(Map.Entry<Integer, MapSection> row : column.getValue().entrySet()) { MapSection section = row.getValue(); section.x -= incrementor; } } } It works ok if I change section.x -= incrementor; to section.x = section.x - (int)incrementor; but if i do that the scrolling doesn't appear as smooth.

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  • Open a new panel via a button Java Swing

    - by abuteau
    I saw a lot of post on StackOverflow relating to this, but unable to solve my problem. I want to open a new Panel by clicking a button. Here is how i try to do it parameterButton = new JButton("Parametres"); parameterButton.addActionListener(new ActionListener(){ public void actionPerformed(ActionEvent e){ createParameterPanel = new DisplayParameterPanel(); createParameterPanel.setVisible(true); add(createParameterPanel); }; }); add(parameterButton); When I click the parameterButton it doesn't open. How can I open a new panel. Thanks,

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  • Java for-loop problem

    - by Dan
    OK so here's my code: http://so.pastebin.com/9swaiuRy The problem is that I am trying to make certain tiles blocked so the player cannot walk on them. However, it's only reading the FIRST tile which is board[0][0] and everything else is not checked.... What am I doing wrong? :( Thank you.

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  • Pointer-like behavior in Java

    - by Shmoo
    I got the following: class A{ int foo; } class B extends A{ public void bar(); } I got a instance of A and want to convert it to an instance of B without losing the reference to the variable foo. For example: A a = new A(); a.foo = 2; B b = a; <-- what I want to do. //use b b.foo = 3; //a.foo should now be 3 Thanks for any help!

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  • Long list of if statements in Java

    - by steve
    Hi, Sorry I can't find a question answering this, I'm almost certain someone else has raised it before. My problem is that I'm writing some system libraries to run embedded devices. I have commands which can be sent to these devices over radio broadcasts. This can only be done by text. inside the system libraries I have a thread which handles the commands which looks like this if (value.equals("A") { doCommandA() } else if (value.equals"B") { doCommandB() } else if etc. The problem is that there are a lot of commands to it will quickly spiral to something out of control. Horrible to look out, painful to debug and mind boggling to understand in a few months time.

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  • initiliase the object in java

    - by harigm
    is it the right Way we initialise the the object? I have a Class Sample(); I want to intialise the Object in my Sample1 Class After intialisation I dont require to use the object of Sample Class. In that Case Can I initialise that object as new Sample(); instead of Sample s = new Sample(), if I am not going to use s anywhere in my Sample1 Class My question, is this a good practice to do that? will there be any after affects

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  • Having access to a private variable from other classes in Java

    - by Crystal
    If I want to create a form that adds people to a List, how do I have access to that List from another class? Where would I define that List so other classes can access the members, the size, etc? For example, if I have Class Foo that has the GUI for my form, along with buttons to add and remove people to the List, it would make sense to me to declare the List as a private instance variable of Class Foo. But then if I have another class, Class Bar, how does it get the values that are currently in that List to update some other graphical components? Or is that the wrong place to declare the List in general? Thanks.

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  • Java: How to write "Arabic" in properties file?

    - by SmoothCriminel
    Hi Experts, I want to write "Arabic" in the message resource bundle (properties) file but when I try to save it I get this error: "Save couldn't be completed Some characters cannot be mapped using "ISO-85591-1" character encoding. Either change encoding or remove the character ..." Can anyone guide please? I want to write: global.username = ??? ???????? How should I write the Arabic of "username" in properties file? So, that internationalization works.. BR SC

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  • Java loop and increment problem

    - by user552961
    Can any one tell me what is the problem in my program? String a[],b[]; int c[] = new int[b.length]; for (int j = 0; j < a.length; j++) { for (int k = 0; k < b.length; k++) { if (b[k].equals(a[j])) { c[k]++; } else { c[k] = 0; } } } I have thousands of words stored in a HashMap. Now I want to check in every file that how many time one word occurred from allWords. Can you point out mistake in my program or give me your idea that how I can do it?

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  • Create a java executable with Eclipse

    - by Micah
    This is a totally newbie question. I'm running Eclipse on Ubuntu. I created a test project that I want to compile to an executable (whataver the linux equivalent is of a Windows .exe file). Here's the contents of my program: public class MyTest { public static void main(String[] args) { System.out.println("You passed in: " + args[0]); } } I want to know how to compile it and then how to execute it from the command line. Thanks!

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  • construct a unique number for a string in java

    - by praveen
    We have a requirement of reading/writing more than 10 million strings into a file. Also we do not want duplicates in the file. Since the strings would be flushed to a file as soon as they are read we are not maintaining it in memory. We cannot use hashcode because of collisions in the hash code due to which we might miss a string as duplicate. Two other approaches i found in my googling: 1.Use a message digest algorithm like MD5 - but it might be too costly to calculate and store. 2.Use a checksum algorithm. [i am not sure if this produces a unique key for a string- can someone please confirm] Is there any other approach avaiable. Thanks.

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  • Java Sorting "queue" list based on DateTime and Z Position (part of school project)

    - by Kuchinawa
    For a school project i have a list of 50k containers that arrive on a boat. These containers need to be sorted in a list in such a way that the earliest departure DateTimes are at the top and the containers above those above them. This list then gets used for a crane that picks them up in order. I started out with 2 Collection.sort() methods: 1st one to get them in the right XYZ order Collections.sort(containers, new Comparator<ContainerData>() { @Override public int compare(ContainerData contData1, ContainerData contData2) { return positionSort(contData1.getLocation(),contData2.getLocation()); } }); Then another one to reorder the dates while keeping the position in mind: Collections.sort(containers, new Comparator<ContainerData>() { @Override public int compare(ContainerData contData1, ContainerData contData2) { int c = contData1.getLeaveDateTimeFrom().compareTo(contData2.getLeaveDateTimeFrom()); int p = positionSort2(contData1.getLocation(), contData2.getLocation()); if(p != 0) c = p; return c; } }); But i never got this method to work.. What i got working now is rather quick and dirty and takes a long time to process (50seconds for all 50k): First a sort on DateTime: Collections.sort(containers, new Comparator<ContainerData>() { @Override public int compare(ContainerData contData1, ContainerData contData2) { return contData1.getLeaveDateTimeFrom().compareTo(contData2.getLeaveDateTimeFrom()); } }); Then a correction function that bumps top containers up: containers = stackCorrection(containers); private static List<ContainerData> stackCorrection(List<ContainerData> sortedContainerList) { for(int i = 0; i < sortedContainerList.size(); i++) { ContainerData current = sortedContainerList.get(i); // 5 = Max Stack (0 index) if(current.getLocation().getZ() < 5) { //Loop through possible containers above current for(int j = 5; j > current.getLocation().getZ(); --j) { //Search for container above for(int k = i + 1; k < sortedContainerList.size(); ++k) if(sortedContainerList.get(k).getLocation().getX() == current.getLocation().getX()) { if(sortedContainerList.get(k).getLocation().getY() == current.getLocation().getY()) { if(sortedContainerList.get(k).getLocation().getZ() == j) { //Found -> move container above current sortedContainerList.add(i, sortedContainerList.remove(k)); k = sortedContainerList.size(); i++; } } } } } } return sortedContainerList; } I would like to implement this in a better/faster way. So any hints are appreciated. :)

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