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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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  • Rendering HTML in rails without actually displaying it

    - by Kevin Whitaker
    Hello all, My current project requires me to assemble a .zip file containing HTML and text-only templates for a user to download, for importing into an email marketing program. I've inherited this project, and currently the code uses a "fake" model (that is a model that does not directly correlate to a database table), in which it stores the entire template in a string, using dynamic variables to populate certain areas. The "fake" model then has a method for creating a zip file. It seems to me that there has to be a better way to do this. I was wondering if there was a way to move the template into a .erb/haml file, and then write a method that would populate the file in preparation for being zipped up? Basically, is there a way to render an HTML and text file, without actually having to display them? Thanks for any help.

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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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  • What goes into the "Controller" in "MVC"?

    - by P72endragon
    I think I understand the basic concepts of MVC - the Model contains the data and behaviour of the application, the View is responsible for displaying it to the user and the Controller deals with user input. What I'm uncertain about is exactly what goes in the Controller. Lets say for example I have a fairly simple application (I'm specifically thinking Java, but I suppose the same principles apply elsewhere). I organise my code into 3 packages called app.model, app.view and app.controller. Within the app.model package, I have a few classes that reflect the actual behaviour of the application. These extends Observable and use setChanged() and notifyObservers() to trigger the views to update when appropriate. The app.view package has a class (or several classes for different types of display) that uses javax.swing components to handle the display. Some of these components need to feed back into the Model. If I understand correctly, the View shouldn't have anything to do with the feedback - that should be dealt with by the Controller. So what do I actually put in the Controller? Do I put the public void actionPerformed(ActionEvent e) in the View with just a call to a method in the Controller? If so, should any validation etc be done in the Controller? If so, how do I feedback error messages back to the View - should that go through the Model again, or should the Controller just send it straight back to View? If the validation is done in the View, what do I put in the Controller? Sorry for the long question, I just wanted to document my understanding of the process and hopefully someone can clarify this issue for me!

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  • C or C++: how do loaders/wrappers work?

    - by guitar-
    Here's an example of what I mean... User runs LOADER.EXE program LOADER.EXE downloads another EXE but keeps it all in memory without saving it to disk Runs the downloaded EXE just as it would if it were executed from disk, but does it straight from memory I've seen a few applications like this, and I've never seen an example or an explanation of how it works. Does anyone know? Another example is having an encrypted EXE embedded in another one. It gets extracted and decrypted in memory, without ever being saved to disk before it gets executed. I've seen that one used in some applications to prevent piracy.

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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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  • I'm maintaining a java class that's 40K lines long.. problem?

    - by Billworth Vandory
    This may be a subjective question leading to deletion but I would really like some feedback. Recently, I moved to another very large enterprise project where I work as a C++ developer. I was aghast to find most classes in the project are anywhere from 8K to 50K lines long with methods that are 1K to 8K lines long. It's mostly business logic dealing with DB tables and data management, full of conditional statements to handle the use cases. Are classes this large common in large enterprise systems? I realize without looking at the code it's hard to make a determination, but have you ever worked on a system with classes this large?

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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 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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  • 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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  • 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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  • (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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  • 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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  • 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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