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  • why toString method does not work here??

    - by user329820
    Hi this is my whole class ,I have added number 2 to the doubly linked list and then I want it to be be print in the concole but it will show this "datastructureproject.Node@f62373" thanks! package datastructureproject; public class DoublyLinkedList { private Node head = new Node(0); private Node tail = new Node(0); private int length = 0; public DoublyLinkedList() { head.setPrev(null); head.setNext(tail); tail.setPrev(head); tail.setNext(null); } public void add(int index, int value) throws IndexOutOfBoundsException { Node cursor = get(index); Node temp = new Node(value); temp.setPrev(cursor); temp.setNext(cursor.getNext()); cursor.getNext().setPrev(temp); cursor.setNext(temp); length++; } private Node get(int index) throws IndexOutOfBoundsException { if (index < 0 || index > length) { throw new IndexOutOfBoundsException(); } else { Node cursor = head; for (int i = 0; i < index; i++) { cursor = cursor.getNext(); } return cursor; } } public long size() { return length; } public boolean isEmpty() { return length == 0; } @Override public String toString() { StringBuffer result = new StringBuffer(); result.append("(head) - "); Node temp = head; while (temp.getNext() != tail) { temp = temp.getNext(); result.append(temp.getValue() + " - "); } result.append("(tail)"); return result.toString(); } public static void main(String[] args){ DoublyLinkedList list = new DoublyLinkedList(); list.add(0,2 ); System.out.println(list.get(0).toString()); } }

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  • When I try to redefine a variable, I get an index out of bounds error

    - by user2770254
    I'm building a program to act as a calculator with memory, so you can give variables and their values. Whenever I'm trying to redefine a variable, a = 5, to a = 6, I get an index out of bounds error. public static void main(String args[]) { LinkedHashMap<String,Integer> map = new LinkedHashMap<String,Integer>(); Scanner scan = new Scanner(System.in); ArrayList<Integer> values = new ArrayList<>(); ArrayList<String> variables = new ArrayList<>(); while(scan.hasNextLine()) { String line = scan.nextLine(); String[] tokens = line.split(" "); if(!Character.isDigit(tokens[0].charAt(0)) && !line.equals("clear") && !line.equals("var")) { int value = 0; for(int i=0; i<tokens.length; i++) { if(tokens.length==3) { value = Integer.parseInt(tokens[2]); System.out.printf("%5d\n",value); if(map.containsKey(tokens[0])) { values.set(values.indexOf(tokens[0]), value); variables.set(variables.indexOf(tokens[0]), tokens[0]); } else { values.add(value); } break; } else if(tokens[i].charAt(0) == '+') { value = addition(tokens, value); System.out.printf("%5d\n",value); variables.add(tokens[0]); if(map.containsKey(tokens[0])) { values.set(values.indexOf(tokens[0]), value); variables.set(variables.indexOf(tokens[0]), tokens[0]); } else { values.add(value); } break; } else if(i==tokens.length-1 && tokens.length != 3) { System.out.println("No operation"); break; } } map.put(tokens[0], value); } if(Character.isDigit(tokens[0].charAt(0))) { int value = 0; if(tokens.length==1) { System.out.printf("%5s\n", tokens[0]); } else { value = addition(tokens, value); System.out.printf("%5d\n", value); } } if(line.equals("clear")) { clear(map); } if(line.equals("var")) { variableList(variables, values); } } } public static int addition(String[] a, int b) { for(String item : a) { if(Character.isDigit(item.charAt(0))) { int add = Integer.parseInt(item); b = b + add; } } return b; } public static void clear(LinkedHashMap<String,Integer> b) { b.clear(); } public static void variableList(ArrayList<String> a, ArrayList<Integer> b) { for(int i=0; i<a.size(); i++) { System.out.printf("%5s: %d\n", a.get(i), b.get(i)); } } I included the whole code because I'm not sure where the error is arising from.

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  • this is my first time asking here, I wanted to create a linked list while sorting it thanks

    - by user2738718
    package practise; public class Node { // node contains data and next public int data; public Node next; //constructor public Node (int data, Node next){ this.data = data; this.next = next; } //list insert method public void insert(Node list, int s){ //case 1 if only one element in the list if(list.next == null && list.data > s) { Node T = new Node(s,list); } else if(list.next == null && list.data < s) { Node T = new Node(s,null); list.next = T; } //case 2 if more than 1 element in the list // 3 elements present I set prev to null and curr to list then performed while loop if(list.next.next != null) { Node curr = list; Node prev = null; while(curr != null) { prev = curr; curr = curr.next; if(curr.data > s && prev.data < s){ Node T = new Node(s,curr); prev.next = T; } } // case 3 at the end checks for the data if(prev.data < s){ Node T = new Node(s,null); prev.next = T; } } } } // this is a hw problem, i created the insert method so i can check and place it in the correct order so my list is sorted This is how far I got, please correct me if I am wrong, I keep inserting node in the main method, Node root = new Node(); and root.insert() to add.

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  • How to detect Out Of Memory condition?

    - by Jaromir Hamala
    I have an application running on Websphere Application Server 6.0 and it crashes nearly every day because of Out-Of-Memory. From verbose GC is certain there are the memory leaks(many of them) Unfortunately the application is provided by external vendor and getting things fixed is slow & painful process. As part of the process I need to gather the logs and heapdumps each time the OOM occurs. Now I'm looking for some way how to automate it. Fundamental problem is how to detect OOM condition. One way would be to create shell script which will periodically search for new heapdumps. This approach seems me a kinda dirty. Another approach might be to leverage the JMX somehow. But I have little or no experience in this area and don't have much idea how to do it. Or is in WAS some kind of trigger/hooks for this? Thank you very much for every advice!

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  • Two pass JSP page rendering

    - by dotsid
    Suppose an example. I have following interface: public interface DataSource<T> { Future<T> fetch(); } This datasource can do asynchronous data fetching. And we have following tag for using datasource in JSP: <html> <d:fetch from="${orderDS}" var="orders"> <c:foreach in="${orders}" var="order"> <div class="order"> <c:out value="${order.title}" /> </div> </c:foreach> </d:fetch> </html> So, what I want? I want JSP rendering engine to call my custom tag (FetchTag in this example) twice. On first call FetchTag will do DataSource.fetch() call and save Future locally as a object field. On second call FetchTag do Future.get() call and will be blocked until data becomes available. Is there any way to do such a thing?

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  • In ArrayBlockingQueue, why copy into ReentrantLock field into local final variable?

    - by mjlee
    In ArrayBlockingQueue, any method that requires lock will get set 'final' local variable before calling 'lock()'. public boolean offer(E e) { if (e == null) throw new NullPointerException(); final ReentrantLock lock = this.lock; lock.lock(); try { if (count == items.length) return false; else { insert(e); return true; } } finally { lock.unlock(); } } Is there any reason to set a local variable 'lock' from 'this.lock' when field 'this.lock' is final also. Additionally, it also set local variable of E[] before acting on. private E extract() { final E[] items = this.items; E x = items[takeIndex]; items[takeIndex] = null; takeIndex = inc(takeIndex); --count; notFull.signal(); return x; } Is there any reason for copying to local final variable?

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  • How to lowercase every element of a collection efficiently?

    - by Chris
    Whats the most efficient way to lower case every element of a list or set? My idea for a List: final List<String> strings = new ArrayList<String>(); strings.add("HELLO"); strings.add("WORLD"); for(int i=0,l=strings.size();i<l;++i) { strings.add(strings.remove(0).toLowerCase()); } is there a better, faster way? How would this exmaple look like for a set? As there is currently no method for applying an operation to each element of a set (or list) can it be done without creating an additional temporary set? Something like this would be nice: Set<String> strings = new HashSet<String>(); strings.apply( function (element) { this.replace(element, element.toLowerCase();) } ); Thanks,

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  • How to detect column conflicts with Hibernate?

    - by Slim
    So let's say I have an ArrayList full of Products that need to be committed to the database via Hibernate. There are already a large number of Products in the database. Each product has an ID. Note this is NOT the PK that is autogenerated by Hibernate. My questions is: what is the best way to detect conflicts with this ID? I am looking for a relatively efficient method of obtaining, from the the database, a List of Products that share an ID with any of the Products in my ArrayList. This is all in a single table called Products and the ID attribute is in column ProductID. The way I've done it is grabbing a list of all Products in the database, and compared each one with each entry in my ArrayList - but that is seriously inefficient and I don't think it would work well with a larger database. How should it be done? Thanks. I say "relatively" efficient because efficiency is not the primary concern, but it shouldn't take noticeably long to test against a table of ~1000-5000 rows. Help? EDIT* I'm very new to hibernate and below is the best I've come up with. How does this look? for(long id : idList){ //idList just holds the IDs of each Product in my ArrayList Query query = session.createQuery("select product from Product product where product.id = :id"); query.setLong("id", id); for(int i = 0; i < query.list().size(); i++){ listOfConflictingProducts.add((Product) query.list().get(i)); } }

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  • How to set a bean property before executing this f:event listener

    - by user
    How to set a bean property from jsf page before executing this f:event listener: <f:event type="preRenderComponent" listener="bean.method}"/> I tried the below code but it does not set the value to the bean property. <f:event type="preRenderComponent" listener="bean.method}"> <f:setPropertyActionListener target="#{bean.howMany}" value="2"/> </f:event> JSF2.1.6 with PF 3.3 EDIT Any issues with this below code? (This works! but I just want to confirm if there are any issues with this!?) <f:event type="preRenderComponent" listener="#{bean.setHowMany(15)}"/> <f:event type="preRenderComponent" listener="#{bean.method}"/>

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  • Where to put common setUp-code for differen testclasses?

    - by Benedikt
    I have several different test classes that require that certain objects are created before those tests can be run. Now I'm wondering if I should put the object initialization code into a separate helper class or superclass. Doing so would surely reduce the amount of duplicate code in my test classes but it would also make them less readable. Is there a guideline or pattern how to deal with common setUp-code for unit tests?

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  • Hibernate custom join clause on association

    - by myso
    I would like to associate 2 entities using hibernate annotations with a custom join clause. The clause is on the usual FK/PK equality, but also where the FK is null. In SQL this would be something like: join b on a.id = b.a_id or b.a_id is null From what I have read I should use the @WhereJoinTable annotation on the owner entity, but I'm puzzled about how I specify this condition...especially the first part of it - referring to the joining entity's id. Does anyone have an example?

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  • Can getAttribute() method of Tomcat ServletContext implementation be called without synchronization?

    - by oo_olo_oo
    I would like to read some parameters during servlet initializtion (in init() method), and store them among servlet context attributes (using getServletContext().setAttribute()). I would like to read these parameters later - during some request processing (using getServletContext().getAttribute()). So, the multiple threads could do this simultaneously. My question is if such an attempt is safe? Could I be sure that multi threaded calls to the getAttribute() don't mess up any internal state of the servlet context? Please take into account that I'm not going to call the setAttribute() anywhere besides the initialization. So, only calls to the getAttribute() are going to be done from multiple threads. But depending on the internal implementation, this also could be dangerous. So, any information about Tomcat's implementation would be appreciated.

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  • Does a HashSet make an internal copy of added Objects?

    - by praks5432
    Let's say I have a function that is recursive and is like this public void someRecur(List<Integer>someList){ if(someBreakCondition) Set.add(someList); for(int i = 0; i < someLen ; i++){ someList.add(someInt); someRecur(someList); someList.remove(someInt); } } Does the remove affect the list that has been put into the set? What should I do to give the set an actual copy of the list?

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  • about Sorting Algorithms

    - by matin1234
    Hi I want to know that we always use Sorting algorithm like (Insertion Sort or Merge Sort,...) just for lists and arrays?? and we do not use these algorithms for stack or queue ??? thanks

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  • Check if table exists

    - by Dmitry
    I have a desktop application with a database embedded in it. When I execute my program I need to check that specific table exists, or create it if not. Given a Connection object named conn for my database, how could I check this?

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  • Keeping messages in queue in case of receiver crash

    - by John Doe
    Hi, We've a Spring JMS message listener container for receiving messages asynchronously. Using DefaultMessageListenerContainer and in sessionTransacted mode. I understand being in sessionTransacted mode means in case of an exception the message will be put back into the queue. But how can I make sure the message won't be deleted from the queue even if the receiver (which is picked the message) crashes or just the machine running it looses power? At first I thought CLIENT_ACKNOWLEDGE acknowledge mode should save me, but apparently it's not the case, Spring calls .acknowledge() no matter what. So here's my question, how can I guarantee the delivery? Using a custom MessageListenerContainer? Using a transaction manager?

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  • How to read log4j output to a web page?

    - by Ran
    I have a web page, used for admin purposes, which runs a task (image fetching from a remote site). In order to be able to debug the task using the browser only, no ssh etc, I'd like to be able to read all log output from the executing thread and spit it out to the web page. The task boils down to: Changing log level for current thread at the beginning of the call and restore when the call is done. Reading all log output by current thread and storing it in a string. So in pseudocode my execute() method would look like this: (I'm using struts2) public String execute() throws Exception { turnLoggingLevelToDebugOnlyForThisThread() ... do stuff... restoreLoggingLevelForThisThread() String logs = readAllLogsByThisThread(); } Can this be done with log4j? I'm using tomcat, struts2, log4j and slf4j.

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  • hibernate search

    - by Odelya
    Hi! I am using Hibernate. I am looking for a free text engine. Before I investigate into it I need your experience. I have in my applications user, role and object table. Where a user is connected to one or more roles, and a role is connected to one or more objects. In my free text search, the user can reach only data that he is allowed to watch by object table. Can Hibernate search help me with it?

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  • How to solve following issues?

    - by lakshmi
    hi im using postgresql database, I want to insert my datas into database,but whenever i run the server,it was display the following Error. Error:org.postgresql.util.PSQLException: FATAL: sorry, too many clients already How to solve this problem.My server.properties file is following. Sever.properties File: serverPortData=9042 serverPortCommand=9078 simocoConnectionURL=jdbc:postgresql://127.0.0.1:5432/vTrack?user=postgres&password=postgres dst=1 DatabaseName=vTrack ServerName=127.0.0.1 User=postgres Password=admin MaxConnections=90 InitialConnections=80 PoolSize=100 MaxPoolSize=100 KeepAliveTime=100 SimocoPoolSize=120 SimocoMaxPoolSize=120 SimocoKeepAliveTime=100 PortNumber=5432 Logging=1 Thanks.

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