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  • Java: autofiltering list?

    - by Jason S
    I have a series of items arriving which are used in one of my data structures, and I need a way to keep track of those items that are retained. interface Item {} class Foo implements Item { ... } class Baz implements Item { ... } class StateManager { List<Foo> fooList; Map<Integer, Baz> bazMap; public List<Item> getItems(); } What I want is that if I do the following: for (int i = 0; i < SOME_LARGE_NUMBER; ++i) { /* randomly do one of the following: * 1) put a new Foo somewhere in the fooList * 2) delete one or more members from the fooList * 3) put a new Baz somewhere in the bazMap * 4) delete one or more members from the bazMap */ } then if I make a call to StateManager.getItems(), I want to return a list of those Foo and Baz items, which are found in the fooList and the bazMap, in the order they were added. Items that were deleted or displaced from fooList and bazMap should not be in the returned list. How could I implement this? SOME_LARGE_NUMBER is large enough that I don't have the memory available to retain all the Foo and Baz items, and then filter them.

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  • Call a method of subclass in Java

    - by eyecreate
    If I have a base class Base thing = null; of which there is a subclass class Subclass extends Base and I instigate it as thing = new Subclass how would I call a method that is specifically in Subclass, but not in Base? ex. Base has only method() Subclass has method() and specialMethod() the method specialMethod() is the one I want to call.

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  • Java apache commons library source license question

    - by llm
    I want to use functionality from a certain method in apache commons StringUtils. I currently do not have the option of just using the library as one would normally do. I found the source for the method I need and my question is: am I free (legally) to use this code (just a method out of the library) or do I have to use the entire library? If its ok, what kind of attribution would I need in my code, if any? Thanks.

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  • Most Elegant Way to write isPrime in java

    - by Anantha Kumaran
    public class Prime { public static boolean isPrime1(int n) { if (n <= 1) { return false; } if (n == 2) { return true; } for (int i = 2; i <= Math.sqrt(n) + 1; i++) { if (n % i == 0) { return false; } } return true; } public static boolean isPrime2(int n) { if (n <= 1) { return false; } if (n == 2) { return true; } if (n % 2 == 0) { return false; } for (int i = 3; i <= Math.sqrt(n) + 1; i = i + 2) { if (n % i == 0) { return false; } } return true; } } public class PrimeTest { public PrimeTest() { } @Test public void testIsPrime() throws IllegalArgumentException, IllegalAccessException, InvocationTargetException { Prime prime = new Prime(); TreeMap<Long, String> methodMap = new TreeMap<Long, String>(); for (Method method : Prime.class.getDeclaredMethods()) { long startTime = System.currentTimeMillis(); int primeCount = 0; for (int i = 0; i < 1000000; i++) { if ((Boolean) method.invoke(prime, i)) { primeCount++; } } long endTime = System.currentTimeMillis(); Assert.assertEquals(method.getName() + " failed ", 78498, primeCount); methodMap.put(endTime - startTime, method.getName()); } for (Entry<Long, String> entry : methodMap.entrySet()) { System.out.println(entry.getValue() + " " + entry.getKey() + " Milli seconds "); } } } I am trying to find the fastest way to check whether the given number is prime or not. This is what is finally came up with. Is there any better way than the second implementation(isPrime2).

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  • Date conversion in Java

    - by llm
    How can I take a string in a format such as: 2008-06-02 00:00:00.0 and convert it to: 02-Jun-2008? Can I somehow take the original string, convert it to a Date object, then use a formatter to get the final output (rather than parsing the string myself)? Thanks!

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  • Adding to arrays and printing arrays in Java

    - by nfoggia
    I need help figuring out how to get the user to input a number of integers no more than 10, and then add them to an array and print them out from the array. The code I have below, when run, asks the user for the integers and then runs forever and doesn't work. What am I doing wrong? public static void main(String[] args) { Scanner input = new Scanner(System.in); // create a new scanner System.out.print("Enter integers between 1 and 100\n "); int[] nextNumber = new int[10]; int i = 0; int number = input.nextInt(); while (i < nextNumber.length){ i++; nextNumber[i] = number; number = input.nextInt(); } int a = 0; while (a < nextNumber.length){ a++; System.out.println(nextNumber[a]); }

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  • Are there any libraries for parsing "number expressions" like 1,2-9,33- in Java

    - by mihi
    Hi, I don't think it is hard, just tedious to write: Some small free (as in beer) library where I can put in a String like 1,2-9,33- and it can tell me whether a given number matches that expression. Just like most programs have in their print range dialogs. Special functions for matching odd or even numbers only, or matching every number that is 2 mod 5 (or something like that) would be nice, but not needed. The only operation I have to perform on this list is whether the range contains a given (nonnegative) integer value; more operations like max/min value (if they exist) or an iterator would be nice, of course. What would be needed that it does not occupy lots of RAM if anyone enters 1-10000000 but the only number I will ever query is 12345 :-) (To implement it, I would parse a list into several (min/max/value/mod) pairs, like 1,10,0,1 for 1-10 or 11,33,1,2 for 1-33odd, or 12,62,2,10 for 12-62/10 (i. e. 12, 22, 32, ..., 62) and then check each number for all the intervals. Open intervals by using Integer.MaxValue etc. If there are no libs, any ideas to do it better/more efficient?)

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  • create a sparse BufferedImage in java

    - by elgcom
    I have to create an image with very large resolution, but the image is relatively "sparse", only some areas in the image need to draw. For example with following code /* this take 5GB memory */ final BufferedImage img = new BufferedImage( 36000, 36000, BufferedImage.TYPE_INT_ARGB); /* draw something */ Graphics g = img.getGraphics(); g.drawImage(....); /* output as PNG */ final File out = new File("out.png"); ImageIO.write(img, "png", out); The PNG image on the end I created is ONLY about 200~300 MB. The question is how can I avoid creating a 5GB BufferedImage at the beginning? I do need an image with large dimension, but with very sparse color information. Is there any Stream for BufferedImage so that it will not take so much memory?

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  • Strange problem with simple multithreading program in Java

    - by Elizabeth
    Hello, I am just starting play with multithreading programming. I would like to my program show alternately character '-' and '+' but it doesn't. My task is to use synchronized keyword. As far I have: class FunnyStringGenerator{ private char c; public FunnyStringGenerator(){ c = '-'; } public synchronized char next(){ if(c == '-'){ c = '+'; } else{ c = '-'; } return c; } } class ThreadToGenerateStr implements Runnable{ FunnyStringGenerator gen; public ThreadToGenerateStr(FunnyStringGenerator fsg){ gen = fsg; } @Override public void run() { for(int i = 0; i < 10; i++){ System.out.print(gen.next()); } } } public class Main{ public static void main(String[] args) throws IOException { FunnyStringGenerator FSG = new FunnyStringGenerator(); ExecutorService exec = Executors.newCachedThreadPool(); for(int i = 0; i < 20; i++){ exec.execute(new ThreadToGenerateStr(FSG)); } } } EDIT: I also testing Thread.sleep in run method instead for loop.

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  • How to place images on top of each other in java

    - by Haxed
    Hi, I have a background image of a road, which I have displayed on a JFrame using an ImageIcon. I want to put a car on top of that background image at a certain (x,y) location. I tried using another ImageIcon and the background does not appear when I run the program , however the car does. import javax.swing.ImageIcon; import javax.swing.JFrame; import javax.swing.JLabel; public class Gui extends JFrame { private ImageIcon northcar = new ImageIcon("src/north.gif"); private ImageIcon usIcon = new ImageIcon("src/trafficLight.jpg"); public Gui() { add(new JLabel(usIcon)); // background image does not appear after the i added the northcar label add(new JLabel(northcar)); // this picture can be seen } public static void main(String[] args) { Gui frame = new Gui(); frame.setTitle("TestImageIcon"); frame.setLocationRelativeTo(null); // Center the frame frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBounds(0, 0, 650, 650); frame.setVisible(true); } } I heard about using a canvas but have no clue. Any ideas ? Many Thanks

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  • How do I display java.lang.* object allocations in Eclipse profiler?

    - by Martin Wickman
    I am profiling an application using the Eclipse profiler. I am particularly interested in number of allocated object instances of classes from java.lang (for instance java.lang.String or java.util.HashMap). I also want to know stuff like number of calls to String.equals() etc. I use the "Object Allocations" tab and I shows all classes in my application and a count. It also shows all int[], byte[], long[] etc, but there is no mention of any standard java classes. For instance, this silly code: public static void main(String[] args) { Object obj[] = new Object[1000]; for (int i = 0; i < 1000; i++) { obj[i] = new StringBuffer("foo" + i); } System.out.println (obj[30]); } Shows up in the Object Allocations tab as 7 byte[]s, 4 char[]s and 2 int[]s. It doesn't matter if I use 1000 or 1 iterations. It seems the profiler simply ignores everything that is in any of the java.* packages. The same applies to Execution Statistics as well. Any idea how to display instances of java.* in the Eclipse Profiler?

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  • Incorrect sizing of a JPanel in a JScrollPane In Java 1.5

    - by Coder
    Hi, I am making an image loading component which consists of a JPanel containing a JScrollPane, which in turn contains another JPanel. What this component does is allows images to be dropped on top of it, after which point the image is loaded and the inner most JPanel is set to the size of the image dropped. This in turn causes the scroll bars to show up and the user can scroll the image. This all works fine. The problem comes in when i try to auto-shrink the image to the maximum visible area in the outer JPanel. In this case i do a uniform scale of the image to be less than or equal to the width and height of the outer JPanel. What happens now is that both the horizontal and vertical scroll bars show up indicating the the inner JPanel is bigger than the visible area (which should not be the case). I verified that the image is scale to the proper dimensions(ie. the maximum width and height is respected). I also verified that if i decrease the maximum height by 3 pixels, then no scroll bars appear. What i believe the problem is, is that panel.getWidth() and panel.getHeight() don't actually return the visible area (maximum area) that sub components can take up. Ie. there is likely some more width and height taken up by the border around the JPanel or something like that. My question is, how do i get around this problem. Functionally all i want is to determine the maximum size a JPanel can be in a JScrollPane, then set the panel to that size and paint an image over top of it and be assured that the scroll bars of the scroll pane will not show up. Right now the scroll bars are set to AS_NEEDED. Thanks!

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  • Setting the height of a row in a JTable in java

    - by Douglas Grealis
    I have been searching for a solution to be able to increase the height of a row in a JTable. I have been using the setRowHeight(int int) method which compiles and runs OK, but no row[s] have been increased. When I use the getRowHeight(int) method of the row I set the height to, it does print out the size I increased the row to, so I'm not sure what is wrong. The code below is a rough illustration how I am trying to solve it. My class extends JFrame. String[] columnNames = {"Column 1", "Column 2", "Column 1 3"}; JTable table = new JTable(new DefaultTableModel(columnNames, people.size())); DefaultTableModel model = (DefaultTableModel) table.getModel(); int count =1; for(Person p: people) { model.insertRow(count,(new Object[]{count, p.getName(), p.getAge()+"", p.getNationality})); count++; } table.setRowHeight(1, 15);//Try set height to 15 (I've tried higher) Can anyone tell me where I am going wrong? I am trying to increase the height of row 1 to 15 pixels?

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  • How to Create Own HashMap in Java?

    - by Taranfx
    I know about hashing algorithm and hashCode() to convert "key" into an equivalent integer (using some mathematically random expression) that is then compressed and stored into buckets. But can someone point me to an implementation or at least data structure that should be used as baseline? I haven't found it anywhere on the web.

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  • Java Interfaces/Implementation naming convention

    - by Amir Rachum
    How do you name different classes / interfaces you create? Sometimes I don't have implementation information to add to the implementation name - like interface FileHandler and class SqlFileHandler. hen this happens I usually name the interface in the "normal" name, like Truck and name the actual class TruckClass. How do you name interfaces and classes in this regard?

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  • Java: Ignoring escapes when parsing XML

    - by Personman
    I'm using a DocumentBuilder to parse XML files. However, the specification for the project requires that within text nodes, strings like " and < be returned literally, and not turned into the corresponding ASCII values. A previous similar question, http://stackoverflow.com/questions/1979785/read-escaped-quote-as-escaped-quote-from-xml, received one answer that seems to be specific to Apache, and another that appears to simply not not do what it says it does. I'd love to be proven wrong on either count, however :) For reference, here is some code: file = new File(fileName); DocBderFac = DocumentBuilderFactory.newInstance(); DocBder = DocBderFac.newDocumentBuilder(); doc = DocBder.parse(file); NodeList textElmntLst = doc.getElementsByTagName(text); Element textElmnt = (Element) textElmntLst.item(0); NodeList txts = textElmnt.getChildNodes(); String txt = ((Node) txts.item(0)).getNodeValue(); System.out.println(txt); I would like that println() to produce things like &quot;3&gt;2&quot; instead of "3>2" which is what currently happens. Thanks!

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  • Android/Java Append String + int

    - by xger86x
    Hi, i have a question, what is the best way to append ints and Strings to build a new String? In the allocation debug tool i see too much allocations if i use the operator +. But i have tried also with StringBuffer and there are still too much allocations. Anyone can help me? Thanks

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