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  • INSERT SQL in Java

    - by Pierre
    Hello. I have a Java application and I want to use SQL database. I have a class for my connection : public class SQLConnection{ private static String url = "jdbc:postgresql://localhost:5432/table"; private static String user = "postgres"; private static String passwd = "toto"; private static Connection connect; public static Connection getInstance(){ if(connect == null){ try { connect = DriverManager.getConnection(url, user, passwd); } catch (SQLException e) { JOptionPane.showMessageDialog(null, e.getMessage(), "Connection Error", JOptionPane.ERROR_MESSAGE); } } return connect; } } And now, in another class I succeeded to print my values but when I attempt to insert a value nothing is happening ... Here's my code : try { Statement state = SQLConnection.getInstance().createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY); Statement state2 = SQLConnection.getInstance().createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE); state2.executeUpdate("INSERT INTO table(field1) VALUES (\"Value\")"); // Here's my problem ResultSet res = state.executeQuery("SELECT * FROM plateau");

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  • Input In Java- How does it work?

    - by Nir Avnon
    Hey guys, with a lot of help from you i was managed to write this nice code (I'm new in it, so kind of exciting.. :) ) And still I have not understand how can I input this code. first of all, I get an this error in the console line (I'm using Eclipse): Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at NumberConverter.main(NumberConverter.java:5). What does that mean? I just want to chack whether it works, and I can't call the function/program any how. I used to call in an "old fashion way", like in scheme, to the function that I wrote and see if something happens. How does it work in java? Do we call the program itself? function? what and where do we write? -I want to chack if it works, doesn't matter how, and I'll be glad to know how can I plugin input. Thank you so much! public class NumberConverter{ public static void main(String[] args) { int i = Integer.parseInt(args[0]); toBinary(i); toOctal(i); toHex(i); } public static void toBinary(int int1){ System.out.println(int1 + " in binary is"); System.out.println(Integer.toBinaryString(int1)); } public static void toOctal(int int1){ System.out.println(int1 + " in octal is"); System.out.println(Integer.toOctalString(int1)); } public static void toHex(int int1){ System.out.println(int1 + " in hex is"); System.out.println(Integer.toHexString(int1)); } }

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  • How to load modules in Java

    - by gerardorn
    I'm building a server that loads modules. Each module is a .jar file. Inside the jar there's all the classes that the module needs. The server needs to read the jar, find the main class (it doesnt have the main method on it is just the class that makes the module work but not as a different program), build an object of that class and store it in a vector of modules so that it can acces to a specific module depending on the job to be done. How can I do that? As far as the server, it is listening and receiving request, but there's no modules to delegate the job to, since my vector of modules is empty.

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  • Does implementing a Java class under an open-source library's package name constitutes a modificatio

    - by Minyu
    Greetings, I understand that this is not the best forum for getting legal advices. But I am still wondering if anybody has some experience around this topic, or can point me to relevant resources that explain it. I have tried to search it online but could not find clear answers. Assuming I am using a Java open-source library from "somecompany", specifically its entities in the "org.somecompany.somepackage". During development, I found that I need to access some of the internals of that package that are not exposed through its public interface. So I thought maybe creating my own classes under the same "org.somecompany.somepackage" name would make that easier. My question is: does this constitutes a modification of the open-source library? The fully qualified name of my classes look like "org.somecompany.somepackage.myclass". It does seem an "extension" of the original library, even though I am not modifying the original library source or binary. I am also not adding my classes to the open-source jar files. Any advice or pointer to resources will be appreciated!

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  • Java how to load modules

    - by gerardorn
    heres my problem: im building a server that loads modules. each module is a .jar file. inside the jar theres all the classes that the module need. the server needs to read the jar, find the main class (it doesnt have the main method on it is just the class that makes the module work but not as a different program), build an object of that class and store it in a vector of modules so that it can acces to a specific module depending on the job to be done. how can i do that? as far as the server, it is listening and reciving request, but thes no modules to delegate the job to, since my vector of modules is empty

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  • How do I manipulate a tree of immutable objects?

    - by Frederik
    I'm building an entire application out of immutable objects so that multi-threading and undo become easier to implement. I'm using the Google Collections Library which provides immutable versions of Map, List, and Set. My application model looks like a tree: Scene is a top-level object that contains a reference to a root Node. Each Node can contain child Nodes and Ports. An object graph might look like this: Scene | +-- Node | +-- Node | +- Port +-- Node | +- Port +- Port If all of these objects are immutable, controlled by a top-level SceneController object: What is the best way to construct this hierarchy? How would I replace an object that is arbitrarily deep in the object tree? Is there a way to support back-links, e.g. a Node having a "parent" attribute?

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  • Getting instance of a class in ArrayList

    - by user1499974
    I have a small problem with ArrayList. You see, I wish to get an instance of RenderNewHUD in my renderer class, which has a list of registered renderers. I did not want to create a variable for this due to limitations and awkwardness. Here is my code. RenderNewHUD hud = renderer.renderList.get(RenderNewHUD()); How exactly can I go along getting the instance of RenderNewHUD without creating a new instance? If you need any more of my code, just ask. Sorry if this is a very dumb question - I have looked EVERYWHERE for an answer.

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  • Which Java debugger do *you* use.

    - by mikevdg
    I spend a lot of time debugging applications in Eclipse using JPDA. There are a few issues with the Eclipse debugger which really annoy me. Can anybody recommend plug-ins, better debuggers or perhaps tricks that I don't know of yet? In the "Variables" tab, you can type in and execute bits of Java code. However, you first need to click on something (I usually click on "this") to give it some context. Then, after you've typed in a lengthy Java expression to debug something and "execute" it, your expression gets replaced with the result, so you need to type it in all over again. Is there some better way, such as a console or something that I'm missing? When you're poking through data structures, the presentation in the debugger leaves much to be desired. You see the internal representation of Lists, Maps, StringBuilders etc. What I want to see is what these objects conceptually contain. Is there a way of doing this, perhaps using some other debugger, or an extension or something? When an Exception is thrown, is there some way of inspecting the state of the application where the Exception was thrown? Currently I need to set breakpoints just before the Exception occurs and then try to reproduce it. When I'm stepping over a line with many statements on it, I can't actually see which of those statements is being executed, except by "stepping in" to each one to see where it takes me. If no source code is found, Eclipse just stares blankly at you. You get a helpful screen saying "Class File Editor / Source code not found" which is completely useless. I'd much prefer to be able to step through the bytecodes so I can at least see what is going on. Does anybody know of a Java debugger that does this better than Eclipse?

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  • Scanner class is skipping lines

    - by user2403304
    I'm new to programing and I'm having a problem with my scanner class. This code is in a loop and when the loop comes around the second, third whatever time I have it set to it skips the first title input. I need help please why is it skipping my title scanner input in the beginning? System.out.println("Title:"); list[i].title=keyboard.nextLine(); System.out.println("Author:"); list[i].author=keyboard.nextLine(); System.out.println("Album:"); list[i].album=keyboard.nextLine(); System.out.println("Filename:"); list[i].filename=keyboard.nextLine();

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  • How to implement a Linked List in Java?

    - by nbarraille
    Hello! I am trying to implement a simple HashTable in Java that uses a Linked List for collision resolution, which is pretty easy to do in C, but I don't know how to do it in Java, as you can't use pointers... First, I know that those structures are already implemented in Java, I'm not planning on using it, just training here... So I created an element, which is a string and a pointer to the next Element: public class Element{ private String s; private Element next; public Element(String s){ this.s = s; this.next = null; } public void setNext(Element e){ this.next = e; } public String getString(){ return this.s; } public Element getNext(){ return this.next; } @Override public String toString() { return "[" + s + "] => "; } } Of course, my HashTable has an array of Element to stock the data: public class CustomHashTable { private Element[] data; Here is my problem: For example I want to implement a method that adds an element AT THE END of the linked List (I know it would have been simpler and more efficient to insert the element at the beginning of the list, but again, this is only for training purposes). How do I do that without pointer? Here is my code (which could work if e was a pointer...): public void add(String s){ int index = hash(s) % data.length; System.out.println("Adding at index: " + index); Element e = this.data[index]; while(e != null){ e = e.getNext(); } e = new Element(s); } Thanks!

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  • Class or interface expected error (java)

    - by David
    When i try to compile this: public static int compareCardhl (Card c1, Card c2) } if (c1.suit > c2.suit) return 1 ; if (c1.suit < c2.suit) return -1 ; if (c1.rank > c2.rank) return 1 ; if (c1.rank < c2.rank) return -1 ; return 0; } i get a lot of class or intereface expected errors. They all point at the if's. i also get a ; expected error at the end of Card c2). whats going wrong here?

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  • Java: Can't implement runnable on a test case: void run() collides

    - by Zombies
    So I have a test case that I want to make into a thread. I cannot extend Thread nor can I implement runnable since TestCase already has a method void run(). The compilation error I am getting is Error(62,17): method run() in class com.util.SeleneseTestCase cannot override method run() in class junit.framework.TestCase with different return type, was class junit.framework.TestResult. What I am trying to do is to scale a Selenium testcase up to perform stress testing. I am not able to use selenium grid/pushtotest.com/amazon cloud at this time (installation issues/install time/resource issues). So this really is more of a Java language issue for me.

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  • java.awt -- when java outputs an image to my monitor (screen), where is the file that is output to the monitor card?

    - by user1405870
    Suppose that I am drawing a set of images using java graphics objects. Suppose that I java is outputting these images to my monitor. Where is the file or files that are sent to the monitor card (the graphical representation files). How can I take this file and save it to disk, or how can I take this file and write it to an array, or how can I take these files and combine the results of their output (to the monitor) into a single file for saving? I don't want to use a screen shot feature, I want to be able to redirect (xor capture also) the output to the monitor to some sort of byte-stream. I note that monitors are much better than semaphores, when you are talking about display capabilities; I don't need a counter example. I might not be asking the correct question. It might be that I want to capture the file while it is still in User Space, before it is put into 'Device Space'. I would like to try and capture the byte stream so that I can convert it to MPEG-4 format. I either need a streaming output from the MPEG-4 converter, coming from the streaming input, or else, I need to take static images at discrete times and convert the images. What format will the output from User Space be in? What format will the Device Space output be in? Try to keep speculation to a minimum. http://docs.oracle.com/javame/config/cdc/opt-pkgs/api/jsr927/index.html I guess that Java has made a means of displaying AWT objects on a television screen. Thank you. Ryan Zoerner

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  • Java synchronizing static list ?

    - by JavaUser
    Hi, In a Java class , i am having a static list so this list is shared across all the objects of this class.The business logic in this class will run periodically which is invoked by some method with out passing instance parameters.Now I want to invoke this run method based on the list(I will add some vales into this list based on JMS) ,this list may empty sometimes and after finishing the run , i am emptying this list.Now my question is , whether I need to synchronize this list or not? Also let me know is there any other way to pass value in one object instance(Thread1) to other object instance (Thread2) other than having Static variable(static list)? Thx

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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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  • Get the package of a Java source file

    - by Oak
    My goal is to find the package (as string) of a Java source file, given as plaintext and not already sorted in folders. I can't just locate the first instance of the keyword package in the file, because it may appear inside a comment. So I was thinking about two alternatives: Scan the file word-by-word, maintaining a "inside-a-comment" flag for the scanner. The first time the package keyword is encountered while not inside a comment, stop the scanning and report the result. Use a regex - should be theoretically possible because block comments do not next in Java, but I tried making such a regex and it turned out to be quite complicated - for me, at least. Another difference between the two approaches is that when scanning manually I can stop the scan when I can be certain the package keyword can no longer appear, saving some time... and I'm not sure I can do something similar with regexes. On the other hand, the decision "when it can no longer appear" is not necessarily simple, though I could use some heuristic for that. I would like to hear any input on this problem, and would welcome any help with the regex. My solution is written in Java as well.

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  • Calling a constructor from method within the same class

    - by Nathan
    I'm new to java and I'm learning about creating object classes. One of my homework assignment requires that I call the constructor at least once within a method of the same object class. I'm getting an error that says The method DoubleMatrix(double[][]) is undefined for the type DoubleMatrix Here's my constructor: public DoubleMatrix(double[][] tempArray) { // Declaration int flag = 0; int cnt; // Statement // check to see if doubArray isn't null and has more than 0 rows if(tempArray == null || tempArray.length < 0) { flag++; } // check to see if each row has the same length if(flag == 0) { for(cnt = 0; cnt <= tempArray.length - 1 || flag != 1; cnt++) { if(tempArray[cnt + 1].length != tempArray[0].length) { flag++; } } } else if(flag == 1) { makeDoubMatrix(1, 1);// call makeDoubMatrix method } }// end constructor 2 Here's the method where I try and call the constructor: public double[][] addMatrix(double[][] tempDoub) { // Declaration double[][] newMatrix; int rCnt, cCnt; //Statement // checking to see if both are of same dimension if(doubMatrix.length == tempDoub.length && doubMatrix[0].length == tempDoub[0].length) { newMatrix = new double[doubMatrix.length][doubMatrix[0].length]; // for loop to add matrix to a new one for(rCnt = 0; rCnt <= doubMatrix.length; rCnt++) { for(cCnt = 0; cCnt <= doubMatrix.length; cCnt++) { newMatrix[rCnt][cCnt] = doubMatrix[rCnt][cCnt] + tempDoub[rCnt][cCnt]; } } } else { newMatrix = new double[0][0]; DoubleMatrix(newMatrix) } return newMatrix; }// end addMatrix method Can someone point me to the right direction and explain why I'm getting an error?

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  • Confusing calling method in Java

    - by vBx
    class Parent { private void method1() { System.out.println("Parent's method1()"); } public void method2() { System.out.println("Parent's method2()"); method1(); } } class Child extends Parent { public void method1() { System.out.println("Child's method1()"); } } class test { public static void main(String args[]) { Parent p = new Child(); p.method2(); } } I'm confuse why does in Parent::method2() when invoking method1() it will cal Parents method1() and not Childs method1 ? I see that this happens only when method1() is private? Can someone explain me why ? Thanks you.

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  • Use constructor or setter method?

    - by user633600
    I am working on a UI code where I have an Action class, something like this - public class MyAction extends Action { public MyAction() { setText("My Action Text"); setToolTip("My Action Tool tip"); setImage("Some Image"); } } When this Action class was created it was pretty much assumed that the Action class wont be customizable (in a sense- its text, tooltip or image will be not be changed anywhere in the code). Of late, now we are in need of changing the action text at some location in code. So I suggested my co-worker to remove the hardcoded action text from the constructor and accept it as an argument, so that everybody is forced to pass the action text. Something like this code below - public class MyAction extends Action { public MyAction(String actionText) { setText(actionText); setTooltip("My Action tool tip); setImage("My Image"); } } He however thinks that since setText() method belongs to base class. It can be flexibly used to pass the action text wherever action instance is created. That way, there is no need to change the existing MyAction class. So his code would look something like this. MyAction action = new MyAction(); //this creates action instance with the hardcoded text action.setText("User required new action text"); //overwrite the exisitng text. I am not sure if that is a correct way to deal with problem. I think in above mentioned case user is anyway going to change the text, so why not force him while constructing the action. The only benefit I see with the original code is that user can create Action class without much thinking about setting text.

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  • Java code optimization on matrix windowing computes in more time

    - by rano
    I have a matrix which represents an image and I need to cycle over each pixel and for each one of those I have to compute the sum of all its neighbors, ie the pixels that belong to a window of radius rad centered on the pixel. I came up with three alternatives: The simplest way, the one that recomputes the window for each pixel The more optimized way that uses a queue to store the sums of the window columns and cycling through the columns of the matrix updates this queue by adding a new element and removing the oldes The even more optimized way that does not need to recompute the queue for each row but incrementally adjusts a previously saved one I implemented them in c++ using a queue for the second method and a combination of deques for the third (I need to iterate through their elements without destructing them) and scored their times to see if there was an actual improvement. it appears that the third method is indeed faster. Then I tried to port the code to Java (and I must admit that I'm not very comfortable with it). I used ArrayDeque for the second method and LinkedLists for the third resulting in the third being inefficient in time. Here is the simplest method in C++ (I'm not posting the java version since it is almost identical): void normalWindowing(int mat[][MAX], int cols, int rows, int rad){ int i, j; int h = 0; for (i = 0; i < rows; ++i) { for (j = 0; j < cols; j++) { h = 0; for (int ry =- rad; ry <= rad; ry++) { int y = i + ry; if (y >= 0 && y < rows) { for (int rx =- rad; rx <= rad; rx++) { int x = j + rx; if (x >= 0 && x < cols) { h += mat[y][x]; } } } } } } } Here is the second method (the one optimized through columns) in C++: void opt1Windowing(int mat[][MAX], int cols, int rows, int rad){ int i, j, h, y, col; queue<int>* q = NULL; for (i = 0; i < rows; ++i) { if (q != NULL) delete(q); q = new queue<int>(); h = 0; for (int rx = 0; rx <= rad; rx++) { if (rx < cols) { int mem = 0; for (int ry =- rad; ry <= rad; ry++) { y = i + ry; if (y >= 0 && y < rows) { mem += mat[y][rx]; } } q->push(mem); h += mem; } } for (j = 1; j < cols; j++) { col = j + rad; if (j - rad > 0) { h -= q->front(); q->pop(); } if (j + rad < cols) { int mem = 0; for (int ry =- rad; ry <= rad; ry++) { y = i + ry; if (y >= 0 && y < rows) { mem += mat[y][col]; } } q->push(mem); h += mem; } } } } And here is the Java version: public static void opt1Windowing(int [][] mat, int rad){ int i, j = 0, h, y, col; int cols = mat[0].length; int rows = mat.length; ArrayDeque<Integer> q = null; for (i = 0; i < rows; ++i) { q = new ArrayDeque<Integer>(); h = 0; for (int rx = 0; rx <= rad; rx++) { if (rx < cols) { int mem = 0; for (int ry =- rad; ry <= rad; ry++) { y = i + ry; if (y >= 0 && y < rows) { mem += mat[y][rx]; } } q.addLast(mem); h += mem; } } j = 0; for (j = 1; j < cols; j++) { col = j + rad; if (j - rad > 0) { h -= q.peekFirst(); q.pop(); } if (j + rad < cols) { int mem = 0; for (int ry =- rad; ry <= rad; ry++) { y = i + ry; if (y >= 0 && y < rows) { mem += mat[y][col]; } } q.addLast(mem); h += mem; } } } } I recognize this post will be a wall of text. Here is the third method in C++: void opt2Windowing(int mat[][MAX], int cols, int rows, int rad){ int i = 0; int j = 0; int h = 0; int hh = 0; deque< deque<int> *> * M = new deque< deque<int> *>(); for (int ry = 0; ry <= rad; ry++) { if (ry < rows) { deque<int> * q = new deque<int>(); M->push_back(q); for (int rx = 0; rx <= rad; rx++) { if (rx < cols) { int val = mat[ry][rx]; q->push_back(val); h += val; } } } } deque<int> * C = new deque<int>(M->front()->size()); deque<int> * Q = new deque<int>(M->front()->size()); deque<int> * R = new deque<int>(M->size()); deque< deque<int> *>::iterator mit; deque< deque<int> *>::iterator mstart = M->begin(); deque< deque<int> *>::iterator mend = M->end(); deque<int>::iterator rit; deque<int>::iterator rstart = R->begin(); deque<int>::iterator rend = R->end(); deque<int>::iterator cit; deque<int>::iterator cstart = C->begin(); deque<int>::iterator cend = C->end(); for (mit = mstart, rit = rstart; mit != mend, rit != rend; ++mit, ++rit) { deque<int>::iterator pit; deque<int>::iterator pstart = (* mit)->begin(); deque<int>::iterator pend = (* mit)->end(); for(cit = cstart, pit = pstart; cit != cend && pit != pend; ++cit, ++pit) { (* cit) += (* pit); (* rit) += (* pit); } } for (i = 0; i < rows; ++i) { j = 0; if (i - rad > 0) { deque<int>::iterator cit; deque<int>::iterator cstart = C->begin(); deque<int>::iterator cend = C->end(); deque<int>::iterator pit; deque<int>::iterator pstart = (M->front())->begin(); deque<int>::iterator pend = (M->front())->end(); for(cit = cstart, pit = pstart; cit != cend; ++cit, ++pit) { (* cit) -= (* pit); } deque<int> * k = M->front(); M->pop_front(); delete k; h -= R->front(); R->pop_front(); } int row = i + rad; if (row < rows && i > 0) { deque<int> * newQ = new deque<int>(); M->push_back(newQ); deque<int>::iterator cit; deque<int>::iterator cstart = C->begin(); deque<int>::iterator cend = C->end(); int rx; int tot = 0; for (rx = 0, cit = cstart; rx <= rad; rx++, ++cit) { if (rx < cols) { int val = mat[row][rx]; newQ->push_back(val); (* cit) += val; tot += val; } } R->push_back(tot); h += tot; } hh = h; copy(C->begin(), C->end(), Q->begin()); for (j = 1; j < cols; j++) { int col = j + rad; if (j - rad > 0) { hh -= Q->front(); Q->pop_front(); } if (j + rad < cols) { int val = 0; for (int ry =- rad; ry <= rad; ry++) { int y = i + ry; if (y >= 0 && y < rows) { val += mat[y][col]; } } hh += val; Q->push_back(val); } } } } And finally its Java version: public static void opt2Windowing(int [][] mat, int rad){ int cols = mat[0].length; int rows = mat.length; int i = 0; int j = 0; int h = 0; int hh = 0; LinkedList<LinkedList<Integer>> M = new LinkedList<LinkedList<Integer>>(); for (int ry = 0; ry <= rad; ry++) { if (ry < rows) { LinkedList<Integer> q = new LinkedList<Integer>(); M.addLast(q); for (int rx = 0; rx <= rad; rx++) { if (rx < cols) { int val = mat[ry][rx]; q.addLast(val); h += val; } } } } int firstSize = M.getFirst().size(); int mSize = M.size(); LinkedList<Integer> C = new LinkedList<Integer>(); LinkedList<Integer> Q = null; LinkedList<Integer> R = new LinkedList<Integer>(); for (int k = 0; k < firstSize; k++) { C.add(0); } for (int k = 0; k < mSize; k++) { R.add(0); } ListIterator<LinkedList<Integer>> mit; ListIterator<Integer> rit; ListIterator<Integer> cit; ListIterator<Integer> pit; for (mit = M.listIterator(), rit = R.listIterator(); mit.hasNext();) { Integer r = rit.next(); int rsum = 0; for (cit = C.listIterator(), pit = (mit.next()).listIterator(); cit.hasNext();) { Integer c = cit.next(); Integer p = pit.next(); rsum += p; cit.set(c + p); } rit.set(r + rsum); } for (i = 0; i < rows; ++i) { j = 0; if (i - rad > 0) { for(cit = C.listIterator(), pit = M.getFirst().listIterator(); cit.hasNext();) { Integer c = cit.next(); Integer p = pit.next(); cit.set(c - p); } M.removeFirst(); h -= R.getFirst(); R.removeFirst(); } int row = i + rad; if (row < rows && i > 0) { LinkedList<Integer> newQ = new LinkedList<Integer>(); M.addLast(newQ); int rx; int tot = 0; for (rx = 0, cit = C.listIterator(); rx <= rad; rx++) { if (rx < cols) { Integer c = cit.next(); int val = mat[row][rx]; newQ.addLast(val); cit.set(c + val); tot += val; } } R.addLast(tot); h += tot; } hh = h; Q = new LinkedList<Integer>(); Q.addAll(C); for (j = 1; j < cols; j++) { int col = j + rad; if (j - rad > 0) { hh -= Q.getFirst(); Q.pop(); } if (j + rad < cols) { int val = 0; for (int ry =- rad; ry <= rad; ry++) { int y = i + ry; if (y >= 0 && y < rows) { val += mat[y][col]; } } hh += val; Q.addLast(val); } } } } I guess that most is due to the poor choice of the LinkedList in Java and to the lack of an efficient (not shallow) copy method between two LinkedList. How can I improve the third Java method? Am I doing some conceptual error? As always, any criticisms is welcome. UPDATE Even if it does not solve the issue, using ArrayLists, as being suggested, instead of LinkedList improves the third method. The second one performs still better (but when the number of rows and columns of the matrix is lower than 300 and the window radius is small the first unoptimized method is the fastest in Java)

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  • JSF - get managed bean by name

    - by Konrad Garus
    I'm trying to write a custom servlet (for AJAX/JSON) in which I would like to reference my @ManagedBeans by name. I'm hoping to map: http://host/app/myBean/myProperty to: @ManagedBean(name="myBean") public class MyBean { public String getMyProperty(); } Is it possible to load a bean by name from a regular servlet? Is there a JSF servlet or helper I could use for it? I seem to be spoilt by Spring in which all this is too obvious.

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  • Real-time graphing in Java

    - by thodinc
    I have an application which updates a variable about between 5 to 50 times a second and I am looking for some way of drawing a continuous XY plot of this change in real-time. Though JFreeChart is not recommended for such a high update rate, many users still say that it works for them. I've tried using this demo and modified it to display a random variable, but it seems to use up 100% CPU usage all the time. Even if I ignore that, I do not want to be restricted to JFreeChart's ui class for constructing forms (though I'm not sure what its capabilities are exactly). Would it be possible to integrate it with Java's "forms" and drop-down menus? (as are available in VB) Otherwise, are there any alternatives I could look into? EDIT: I'm new to Swing, so I've put together a code just to test the functionality of JFreeChart with it (while avoiding the use of the ApplicationFrame class of JFree since I'm not sure how that will work with Swing's combo boxes and buttons). Right now, the graph is being updated immediately and CPU usage is high. Would it be possible to buffer the value with new Millisecond() and update it maybe twice a second? Also, can I add other components to the rest of the JFrame without disrupting JFreeChart? How would I do that? frame.getContentPane().add(new Button("Click")) seems to overwrite the graph. package graphtest; import java.util.Random; import javax.swing.JFrame; import org.jfree.chart.ChartFactory; import org.jfree.chart.ChartPanel; import org.jfree.chart.JFreeChart; import org.jfree.chart.axis.ValueAxis; import org.jfree.chart.plot.XYPlot; import org.jfree.data.time.Millisecond; import org.jfree.data.time.TimeSeries; import org.jfree.data.time.TimeSeriesCollection; public class Main { static TimeSeries ts = new TimeSeries("data", Millisecond.class); public static void main(String[] args) throws InterruptedException { gen myGen = new gen(); new Thread(myGen).start(); TimeSeriesCollection dataset = new TimeSeriesCollection(ts); JFreeChart chart = ChartFactory.createTimeSeriesChart( "GraphTest", "Time", "Value", dataset, true, true, false ); final XYPlot plot = chart.getXYPlot(); ValueAxis axis = plot.getDomainAxis(); axis.setAutoRange(true); axis.setFixedAutoRange(60000.0); JFrame frame = new JFrame("GraphTest"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); ChartPanel label = new ChartPanel(chart); frame.getContentPane().add(label); //Suppose I add combo boxes and buttons here later frame.pack(); frame.setVisible(true); } static class gen implements Runnable { private Random randGen = new Random(); public void run() { while(true) { int num = randGen.nextInt(1000); System.out.println(num); ts.addOrUpdate(new Millisecond(), num); try { Thread.sleep(20); } catch (InterruptedException ex) { System.out.println(ex); } } } } }

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  • JSON Formatting with Jersey, Jackson, & json.org/java Parser using Curl Command

    - by socal_javaguy
    Using Java 6, Tomcat 7, Jersey 1.15, Jackson 2.0.6 (from FasterXml maven repo), & www.json.org parser, I am trying to pretty print the JSON String so it will look indented by the curl -X GET command line. I created a simple web service which has the following architecture: My POJOs (model classes): Family.java import javax.xml.bind.annotation.XmlRootElement; @XmlRootElement public class Family { private String father; private String mother; private List<Children> children; // Getter & Setters } Children.java import javax.xml.bind.annotation.XmlRootElement; @XmlRootElement public class Children { private String name; private String age; private String gender; // Getters & Setters } Using a Utility Class, I decided to hard code the POJOs as follows: public class FamilyUtil { public static Family getFamily() { Family family = new Family(); family.setFather("Joe"); family.setMother("Jennifer"); Children child = new Children(); child.setName("Jimmy"); child.setAge("12"); child.setGender("male"); List<Children> children = new ArrayList<Children>(); children.add(child); family.setChildren(children); return family; } } My web service: import java.io.IOException; import javax.ws.rs.GET; import javax.ws.rs.Path; import javax.ws.rs.PathParam; import javax.ws.rs.Produces; import javax.ws.rs.core.MediaType; import org.codehaus.jackson.JsonGenerationException; import org.codehaus.jackson.map.JsonMappingException; import org.codehaus.jackson.map.ObjectMapper; import org.codehaus.jettison.json.JSONException; import org.json.JSONObject; import org.json.JSONTokener; import com.myapp.controller.myappController; import com.myapp.resource.output.HostingSegmentOutput; import com.myapp.util.FamilyUtil; @Path("") public class MyWebService { @GET @Produces(MediaType.APPLICATION_JSON) public static String getFamily() throws IOException, JsonGenerationException, JsonMappingException, JSONException, org.json.JSONException { ObjectMapper mapper = new ObjectMapper(); String uglyJsonString = mapper.writeValueAsString(FamilyUtil.getFamily()); System.out.println(uglyJsonString); JSONTokener tokener = new JSONTokener(uglyJsonString); JSONObject finalResult = new JSONObject(tokener); return finalResult.toString(4); } } When I run this using: curl -X GET http://localhost:8080/mywebservice I get this in my Eclipse's console: {"father":"Joe","mother":"Jennifer","children":[{"name":"Jimmy","age":"12","gender":"male"}]} But from the curl command on the command line (this response is more important): "{\n \"mother\": \"Jennifer\",\n \"children\": [{\n \"age\": \"12\",\n \"name\": \"Jimmy\",\n \"gender\": \"male\"\n }],\n \"father\": \"Joe\"\n}" This is adding newline escape sequences and placing double quotes (but not indenting like it should it does have 4 spaces after the new line but its all in one line). Would appreciate it if someone could point me in the right direction.

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  • using java Calendar

    - by owca
    I have a simple task. There are two classes : Ticket and Date. Ticket contains event, event place and event date which is a Date object. I also need to provide a move() method for Date object, so I used Calendar and Calendar's add(). Everything looks fine apart of the output. I constantly get 5,2,1 as the date's day,month,year. Lines with asterix return proper date. The code : Ticket class : public class Ticket { private String what; private String where; private Date when; public Ticket(String s1, String s2, Data d){ this.what = s1; this.where = s2; this.when = d; } *public Date giveDate(){ System.out.println("when in giveDate() "+this.when); return this.when; } public String toString(){ return "what: "+this.what+"\n"+"where: "+this.where+"\n"+"when: "+this.when; } } Date class: import java.util.Calendar; import java.util.GregorianCalendar; public class Date { public int day; public int month; public int year; public Date(int x, int y, int z){ *System.out.println("x: "+x); *System.out.println("y: "+y); *System.out.println("z: "+z); this.day = x; this.month = y; this.year = z; *System.out.println("this.day: "+this.day); *System.out.println("this.month: "+this.month); *System.out.println("this.year: "+this.year); } public Date move(int p){ *System.out.println("before_change: "+this.day+","+this.month+","+this.year); Calendar gc = new GregorianCalendar(this.year, this.month, this.day); System.out.println("before_adding: "+gc.DAY_OF_MONTH+","+gc.MONTH+","+gc.YEAR); gc.add(Calendar.DAY_OF_YEAR, p); System.out.println("after_adding: "+gc.DAY_OF_MONTH+","+gc.MONTH+","+gc.YEAR); this.year = gc.YEAR; this.day = gc.DAY_OF_MONTH; this.month = gc.MONTH; return this; } @Override public String toString(){ return this.day+","+this.month+","+this.year; } } Main for testing : public class Main { public static void main(String[] args) { Date date1=new Date(30,4,2002); Ticket event1=new Ticket("Peter Gabriel's gig", "London",date1 ); Ticket event2=new Ticket("Diana Kroll's concert", "Glasgow",date1 ); Date date2=event2.giveDate(); date2.move(30); Ticket event3=new Ticket("X's B-day", "some place",date2 ); System.out.println(date1); System.out.println(event1); System.out.println(event2); System.out.println(event3); } } And here's my output. I just can't get it where 5,2,1 come from :/ x: 30 y: 4 z: 2002 this.day: 30 this.month: 4 this.year: 2002 when in giveDate() 6,12,2004 before_change: 6,12,2004 before_adding: 5,2,1 after_adding: 5,2,1 5,2,1 what: Peter Gabriel's gig where: London when: 5,2,1 (...)

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  • Managing highly repetitive code and documentation in Java

    - by polygenelubricants
    Highly repetitive code is generally a bad thing, and there are design patterns that can help minimize this. However, sometimes it's simply inevitable due to the constraints of the language itself. Take the following example from java.util.Arrays: /** * Assigns the specified long value to each element of the specified * range of the specified array of longs. The range to be filled * extends from index <tt>fromIndex</tt>, inclusive, to index * <tt>toIndex</tt>, exclusive. (If <tt>fromIndex==toIndex</tt>, the * range to be filled is empty.) * * @param a the array to be filled * @param fromIndex the index of the first element (inclusive) to be * filled with the specified value * @param toIndex the index of the last element (exclusive) to be * filled with the specified value * @param val the value to be stored in all elements of the array * @throws IllegalArgumentException if <tt>fromIndex &gt; toIndex</tt> * @throws ArrayIndexOutOfBoundsException if <tt>fromIndex &lt; 0</tt> or * <tt>toIndex &gt; a.length</tt> */ public static void fill(long[] a, int fromIndex, int toIndex, long val) { rangeCheck(a.length, fromIndex, toIndex); for (int i=fromIndex; i<toIndex; i++) a[i] = val; } The above snippet appears in the source code 8 times, with very little variation in the documentation/method signature but exactly the same method body, one for each of the root array types int[], short[], char[], byte[], boolean[], double[], float[], and Object[]. I believe that unless one resorts to reflection (which is an entirely different subject in itself), this repetition is inevitable. I understand that as a utility class, such high concentration of repetitive Java code is highly atypical, but even with the best practice, repetition does happen! Refactoring doesn't always work because it's not always possible (the obvious case is when the repetition is in the documentation). Obviously maintaining this source code is a nightmare. A slight typo in the documentation, or a minor bug in the implementation, is multiplied by however many repetitions was made. In fact, the best example happens to involve this exact class: Google Research Blog - Extra, Extra - Read All About It: Nearly All Binary Searches and Mergesorts are Broken (by Joshua Bloch, Software Engineer) The bug is a surprisingly subtle one, occurring in what many thought to be just a simple and straightforward algorithm. // int mid =(low + high) / 2; // the bug int mid = (low + high) >>> 1; // the fix The above line appears 11 times in the source code! So my questions are: How are these kinds of repetitive Java code/documentation handled in practice? How are they developed, maintained, and tested? Do you start with "the original", and make it as mature as possible, and then copy and paste as necessary and hope you didn't make a mistake? And if you did make a mistake in the original, then just fix it everywhere, unless you're comfortable with deleting the copies and repeating the whole replication process? And you apply this same process for the testing code as well? Would Java benefit from some sort of limited-use source code preprocessing for this kind of thing? Perhaps Sun has their own preprocessor to help write, maintain, document and test these kind of repetitive library code? A comment requested another example, so I pulled this one from Google Collections: com.google.common.base.Predicates lines 276-310 (AndPredicate) vs lines 312-346 (OrPredicate). The source for these two classes are identical, except for: AndPredicate vs OrPredicate (each appears 5 times in its class) "And(" vs Or(" (in the respective toString() methods) #and vs #or (in the @see Javadoc comments) true vs false (in apply; ! can be rewritten out of the expression) -1 /* all bits on */ vs 0 /* all bits off */ in hashCode() &= vs |= in hashCode()

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