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  • Is it expensive to hold on to PreparedStatements? (Java & JDBC)

    - by sbook
    I'm trying to figure out if it's efficient for me to cache all of my statements when I create my database connection or if I should only create those that are most used and create the others if/when they're needed.. It seems foolish to create all of the statements in all of the client threads. Any feedback would be greatly appreciated.

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  • Java: Superclass to construct a subclass on certain conditions, possible?

    - by ramihope
    I have this condition public class A { public action() { System.out.println("Action done in A"); } } public class B extends A { public action() { System.out.println("Action done in B"); } } when I create an instance of B, the action will do just actions in B, as it overrides the action of the superclass. the problem is that in my project, the super class A is already used too many times, and I am looking for a way that under certain conditions, when i create an instance of A it makes a check and if it is true, replace itself with B. public class A { public A() { if ([condition]) { this = new B(); } } public action() { System.out.println("Action done in A"); } } A a = new A(); a.action(); // expect to see "Action done in B"... is this possible in some way?

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  • Java: Anyone know of a library that detects the quality of an internet connection?

    - by Zombies
    I know a simple URLConnection to google can detect if I am connected to the internet, after all I am confident that the internet is all well and fine If I cant connect to google. But what I am looking for at this juncture is a library that can measure how effective my connection to the internet is in terms of BOTH responsiveness and bandwidth available. BUT, I do not want to measure how much bandwidth is potentially available as that is too resource intensive. I really just need to be able to test wether or not I can recieve something like X kB's in Y amount of time. Does such a library already exist?

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  • Developer salaries to rise?

    - by rmbarnes
    I have heard people say that the large fall in people graduating with CS based degrees will soon cause developer salaries to rise due to the effects of a smaller supply but ever increasing demand. Do people really think that this is true? To my mind there are a couple of reasons this won't happen: Outsourcing With 'DIY' style languages like PHP and the attitudes of many of the communities behind these languages becoming ever more popular (e.g. the learn yourself, don't need to go to university way of thinking) not many employers will care if developers have degrees in CS or not.

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  • Java: equivalent to C's strnicmp? (both startsWith and ignoreCase)

    - by Jason S
    String string1 = "abCdefGhijklMnopQrstuvwYz"; String string2 = "ABC"; I had been using string1.startsWith(string2), which would return false in the above example, but now I need to ignore case sensitivity, and there is not a String.startsWithIgnoreCase(). Besides doing string1.toLowerCase.startsWith(string2.toLowerCase()); is there an efficient way to see if string1 starts with string2 in a case-insensitive way?

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  • Fastest way to read/store lots of multidimensional data? (Java)

    - by RemiX
    I have three questions about three nested loops: for (int x=0; x<400; x++) { for (int y=0; y<300; y++) { for (int z=0; z<400; z++) { // compute and store value } } } And I need to store all computed values. My standard approach would be to use a 3D-array: values[x][y][z] = 1; // test value but this turns out to be slow: it takes 192 ms to complete this loop, where a single int-assignment int value = 1; // test value takes only 66 ms. 1) Why is an array so relatively slow? 2) And why does it get even slower when I put this in the inner loop: values[z][y][x] = 1; // (notice x and z switched) This takes more than 4 seconds! 3) Most importantly: Can I use a data structure that is as quick as the assignment of a single integer, but can store as much data as the 3D-array?

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  • How to write a cgi script in perl that accepts output (an image file) from a urlconnection in a Java applet and writes it to the server?

    - by Brad Rock
    I created a Java applet for my web page that creates an image file. I want users to be able to run the applet and create unique images, click a button, and have the image they created be saved to the web server. I think I have the code down for writing the image to a URLconnection in the Java applet itself after having successfully written a file while running the applet on my system rather than the web page and saving a file to the local disk, and then altering a few things to write to a URLConnection instead of to the local disk (although we shall see how that works too). I am now trying to write a cgi script in perl that takes the image output from the URLConnection and writes the image to a file on my web server (note: I am a newbie to perl). I have found many examples of how to do something similar with simple text coming from an applet and then writing it to a text file, but I want to know how to apply the same concept to an image. Particularly, how do I read in the image? I've seen text input get read by using read(STDIN, $some_variable)--does the same thing work with an image? Likewise, how do I write the image file? What function do I use? Thanks for your help. I know that I am rather naive about all of this.

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  • Java/Swing: JTable.rowAtPoint doesn't work correctly for points outside the table?

    - by Jason S
    I have this code to get a row from a JTable that is generated by a DragEvent for a DropTarget in some component C which may or may not be the JTable: public int getRowFromDragEvent(DropTargetDragEvent event) { Point p = event.getLocation(); if (event.getSource() != this.table) { SwingUtilities.convertPointToScreen(p, event.getDropTargetContext().getComponent()); SwingUtilities.convertPointFromScreen(p, this.table); if (!this.table.contains(p)) { System.out.println("outside table, would be row "+this.table.rowAtPoint(p)); } } return this.table.rowAtPoint(p); } The System.out.println is just a hack right now. What I'm wondering, is why the System.out.println doesn't always print "row -1". When the table is empty it does, but if I drag something onto the table's header row, I get the println with "row 0". This seems like a bug... or am I not understanding how rowAtPoint() works?

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  • Using Java, Need to establish an https connection via proxy.

    - by Zombies
    I need to establish and send/read over/from an https connection (to a website of course) but through an http proxy or SOCKS proxy. A few other requirements supports blocking (I can't use non-blocking/nio) isn't set as an environment or some other global scope property (there are multiple threads accessing) I was looking into HttpCore components but I did not see any support for blocking https.

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  • How to get just free heap size (not together w stack/method mem) in Java?

    - by Pentium10
    I want to calculate the heap usage for my app. I would like to get a procent value of Heap size only. How do I get the value in code for the current running app? EDIT The upvoted answer is NOT complete/correct. The values returned by those methods include stack and method area too, and I need to monitor only heap size. With that code I got HeapError exception when I reached 43%, so I can't use those methods to monitor just heap.

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  • (This is for a project, so yes it is homework) How would I finish this java code?

    - by user2924318
    The task is to create arrays using user input (which I was able to do), then for the second part, use a separate method to sort the array in ascending order then output it. I have gotten it to do everything I need except I don't know how I would get it to sort. The directions say to use a while loop from 0 to the length to find the minimum value then swap that with the 1st, but I don't know how to do this. This is what I have so far: public static void main(String[] args) { Scanner in = new Scanner(System.in); int storage = getNumDigits(in); if(storage == 0){ System.out.print("No digits to store? OK, goodbye!"); System.exit(0); } int []a = new int [storage]; a = getDigits(a, in); displayDigits(a); selectionSort(a); } private static int getNumDigits(Scanner inScanner) { System.out.print("Please enter the number of digits to be stored: "); int stored = inScanner.nextInt(); while(stored < 0){ System.out.println("ERROR! You must enter a non-negative number of digits!"); System.out.println(); System.out.print("Please enter the number of digits to be stored: "); stored = inScanner.nextInt(); } return stored; } private static int[] getDigits(int[] digits, Scanner inScanner) { int length = digits.length; int count = 0; int toBeStored = 0; while(count < length){ System.out.print("Enter integer " +count +": "); toBeStored = inScanner.nextInt(); digits[count] = toBeStored; count++; } return digits; } private static void displayDigits(int[] digits) { int len = digits.length; System.out.println(); System.out.println("Array before sorting:"); System.out.println("Number of digits in array: " +len); System.out.print("Digits in array: "); for(int cnt = 0; cnt < len-1; cnt++){ System.out.print(digits[cnt] + ", "); } System.out.println(digits[len-1]); } private static void selectionSort(int[] digits) { int l = digits.length; System.out.println(); System.out.println("Array after sorting:"); System.out.println("Number of digits in array: " +l); System.out.print("Digits in array: "); int index = 0; int value = digits[0]; int indVal = digits[index]; while(index < l){ indVal = digits[index]; if(indVal <= value){ indVal = value; digits[index] = value; index++; } else if(value < indVal){ index++; } System.out.print(value); //This is where I don't know what to do. } }

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  • Interrupting a thread from inside a runnable class? (java)

    - by kyeana
    I am trying to set up a method inside a class that implements the runnable interface that will set the interrupt status of that class. The reason i want to be able to do it from inside the class is there is some other clean up stuff that i need to take care of as well, and i would like to be able to do it all by calling one method instead of calling, for example: Gui gui = new Gui() // class that implements runnable Thread guiThread = new Thread(gui, "gui thread"); guiThread.start() ... ... guiThread.interrupt(); gui.cancel(); Currently my cancel code looks like this, however it isn't correctly setting the interrupt status of this thread. public void cancel() { Thread.currentThread().interrupt(); // other clean up code here. } Any advice on if/how i could get this working? Thanks. EDIT: I when i tried to get the cancel working, i commented out the guiThread.interrupt(), so that i wasn't just setting the status the reseting the status.

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  • Java: If I overwrite the .equals method, can I still test for reference equality with ==?

    - by shots fired
    I have the following situation: I need to sort trees based by height, so I made the Tree's comparable using the height attribute. However, I was also told to overwrite the equals and hashCode methods to avoid unpredictable behaviour. Still, sometimes I may want to compare the references of the roots or something along those lines using ==. Is that still possible or does the == comparison call the equals method?

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  • SQLite - executeUpdate exception not caught when database does not exist? (Java)

    - by giant91
    So I was purposely trying to break my program, and I've succeeded. I deleted the sqlite database the program uses, while the program was running, after I already created the connection. Then I attempted to update the database as seen below. Statement stmt; try { stmt = Foo.con.createStatement(); stmt.executeUpdate("INSERT INTO "+table+" VALUES (\'" + itemToAdd + "\')"); } catch(SQLException e) { System.out.println("Error: " + e.toString()); } The problem is, it didn't catch the exception, and continued to run as if the database was updated successfully. Meanwhile the database didn't even exist at that point since this was after I deleted it. Doesn't it check if the database still exists when updating? Do I have to check the database connection manually, every time I update to ensure that the database wasn't corrupted/deleted? Is this the way it is normally done, or is there a simpler/more robust approach? Thank you.

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  • Problems With SWT on Mac

    - by Jav
    I've got a java project that uses an SWT UI and I'm having trouble deploying it on any Mac OS X computers. The program itself works perfectly on Windows when it is either run from within Eclipse or from a jar file. On Mac, the program also works fine in Eclipse, but when I try to run it from a jar file, I get the following error: 2010-04-30 13:33:04.564 java[17825:41b] *** _NSAutoreleaseNoPool(): Object 0x10b9b0 of class NSCFString autoreleased with no pool in place - just leaking Stack: (0x944acf4f 0x943b9432 0x678fb79 0x35a19b1 0x359ba7f) 2010-04-30 13:33:04.566 java[17825:41b] *** _NSAutoreleaseNoPool(): Object 0x115ef0 of class NSCFNumber autoreleased with no pool in place - just leaking Stack: (0x944acf4f 0x943b9432 0x678a0b0 0x35a19b1 0x359ba7f) 2010-04-30 13:33:04.567 java[17825:41b] *** _NSAutoreleaseNoPool(): Object 0x121000 of class NSCFString autoreleased with no pool in place - just leaking Stack: (0x944acf4f 0x943b9432 0x678fb79 0x35a19b1) 2010-04-30 13:33:04.581 java[17825:41b] *** _NSAutoreleaseNoPool(): Object 0x123720 of class NSPathStore2 autoreleased with no pool in place - just leaking Stack: (0x944acf4f 0x943ba637 0x943c238f 0x943c1e8e 0x943c694b 0x678992e 0x35a19b1) 2010-04-30 13:33:04.582 java[17825:41b] *** _NSAutoreleaseNoPool(): Object 0x12d660 of class NSPathStore2 autoreleased with no pool in place - just leaking Stack: (0x944acf4f 0x943ba637 0x943b9739 0x943c3eb2 0x943c6b22 0x678992e 0x35a19b1) ... ... ... The actual error is much larger, and continues until the program crashes. I know that I am using the correct swt.jar file and I have tried running the program with the -XstartOnFirstThread VM argument, but still have not had any luck. Does anybody have any ideas or any suggestions where I could start looking for a solution? Thanks.

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