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  • Java generic Interface performance

    - by halfwarp
    Simple question, but tricky answer I guess. Does using Generic Interfaces hurts performance? Example: public interface Stuff<T> { void hello(T var); } vs public interface Stuff { void hello(Integer var); <---- Integer used just as an example } My first thought is that it doesn't. Generics are just part of the language and the compiler will optimize it as though there were no generics (at least in this particular case of generic interfaces). Is this correct?

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  • Java loop to collect the second and third elements every three in an array

    - by mhollander38
    I have a file with data in the form timestamp, coordinate, coordinate, seperated by spaces, as here; 14:25:01.215 370.0 333.0 I need to loop through and add the coordinates only to an array. The data from the file is read in and put into as String[] called info, from split(" "). I have two problems, I think the end of the file has a extra " " which I need to lose appropriately and I also want confirmation/suggestions of my loop, at the moment I am getting sporadic out of bounds exceptions. My loop is as follows; String[] info; info = dataHolder.split(" "); ArrayList<String> coOrds1 = new ArrayList<String>(); for (int counter = 0; counter < info.length; counter = counter+3) { coOrds1.add(info[counter+1]); coOrds1.add(info[counter+2]); } Help and suggestions appreciated. The text file is here but the class receives in a UDP packet from another class so I am unsure if this potentially adds " " at the end or not.

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  • Java : Count even values in a Binary Search Tree recursively

    - by user307682
    Hi, I need to find out how many even values are contained in a binary tree. this is my code. private int countEven(BSTNode root){ if ((root == null)|| (root.value%2==1)) return 0; return 1+ countEven(root.left) + countEven(root.right); } this i just coded as i do not have a way to test this out. I'm not able to test it out at the moment but need an answer so badly. any help is deeply appreciated.

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  • Java order jlist by status

    - by Takami
    i have a small problem, i don't know how to sort my jlist by status which is retrieved from database. i want sort by "online" and "offline", i mean online computers go first and then offline computers, i have this code now, it just makes the icon+text for the jlist Can you tell me how can i filter/sortby status? public void acx_pc(String query) { try { Statement st = con.createStatement(); ResultSet rs = st.executeQuery(query); String comb; Map<Object, Icon> icons = new HashMap<>(); ArrayList<String> pc_list = new ArrayList<>(); int i = 0; while (rs.next()) { //Getting info from DB String pc_name = rs.getString("nombre_pc"); String pc_ip = rs.getString("IP"); String status = rs.getString("estado"); //Setting text for the jList comb = pc_name + " - " + pc_ip; //Comparing Status switch (status) { case "online": //This is just for rendering an image+text to Jlist icons.put(comb, new ImageIcon(getClass().getResource("/Imagenes/com_on_30x30.png"))); break; case "offline": //This is just for rendering an image to Jlist icons.put(comb, new ImageIcon(getClass().getResource("/Imagenes/com_off_30x30.png"))); break; } //Adding info to ArrayList pc_list.add(i, comb); i++; } con.close(); // Setting the list/text on Jlist Home.computer_jlist.setListData(pc_list.toArray()); // create a cell renderer to add the appropriate icon Home.computer_jlist.setCellRenderer(new pc_cell_render(icons)); } catch (Exception e) { System.out.println("Error aqui: " + e); } } I want to do something like (should automatically order) http://imageshack.us/a/img27/9018/2mx1.png and not: http://imageshack.us/a/img407/346/e9r.png

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  • Big-Oh running time of code in Java (are my answers accurate

    - by Terry Frederick
    the Method hasTwoTrueValues returns true if at least two values in an array of booleans are true. Provide the Big-Oh running time for all three implementations proposed. // Version 1 public boolean has TwoTrueValues( boolean [ ] arr ) { int count = 0; for( int i = 0; i < arr. length; i++ ) if( arr[ i ] ) count++; return count >= 2; } // Version 2 public boolean hasTwoTrueValues( boolean [ ] arr ) { for( int i = 0; i < arr.length; i++ ) for( int j = i + 1; j < arr.length; j++ ) if( arr[ i ] && arr[ j ] ) return true; } // Version 3 public boolean hasTwoTrueValues( boolean [ ] arr ) { for( int i = 0; i < arr.length; i++ if( arr[ i ] ) for( int j = i + 1; j < arr.length; j++ ) if( arr[ j ] ) return true; return false; } For Version 1 I say the running time is O(n) Version 2 I say O(n^2) Version 3 I say O(n^2) I am really new to this Big Oh Notation so if my answers are incorrect could you please explain and help.

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  • Java split is eating my characters.

    - by Fenris_uy
    Hi, I have a string like this String str = "la$le\$li$lo". I want to split it to get the following output "la","le\$li","lo". The \$ is a $ escaped so it should be left in the output. But when I do str.split("[^\\\\]\\$") y get "l","le\$l","lo". From what I get my regex is matching a$ and i$ and removing then. Any idea of how to get my characters back? Thanks

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  • Getter/Setter Problem in Java?

    - by Praveen Chandrasekaran
    Hi Folks, I want to pass the String value between the classes both are same package. so i created the the classs like the code: public class Map_Delegate { String myLatitude; String myLongitude; String myName; private String TAG = "Map_Delegate"; public String getMyName() { return this.myName; } public void setMyName(String value) { Log.v(TAG, value); this.myName = value; } public String getMyLatitude() { return this.myLatitude; } public void setMyLatitude(String value) { Log.v(TAG, value); this.myLatitude = value; } public String getMyLongitude() { return this.myLongitude; } public void setMyLongitude(String value) { Log.v(TAG, value); this.myLongitude = value; } } But it can't pass the value. I done like this code to set the value: Map_Delegate map = new Map_Delegate(); map.setMyName(first_name_temp + " " + last_name_temp); map.setMyLatitude(homeLatitude_temp); map.setMyLongitude(homeLongitude_temp); code to get the value: Map_Delegate map = new Map_Delegate(); name_val = getMyName(); lat_val = getMyLatitude(); long_val = getMyLongitude(); Why get the Null value can you Guess? All classes in the same package and public .AnyIdea?

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  • Java How to find a value in a linked list iteratively and recursively

    - by Roxy
    Hi I have a method that has a reference to a linked list and a int value. So, this method would count and return how often the value happens in the linked list. So, I decided to make a class, public class ListNode{ public ListNode (int v, ListNode n) {value = v; next = n;) public int value; public ListNode next; } Then, the method would start with a public static int findValue(ListNode x, int valueToCount){ // so would I do it like this?? I don't know how to find the value, // like do I check it? for (int i =0; i< x.length ;i++){ valueToCount += valueToCount; } So, I CHANGED this part, If I did this recursively, then I would have public static int findValue(ListNode x, int valueToCount) { if (x.next != null && x.value == valueToCount { return 1 + findValue(x, valueToCount);} else return new findvalue(x, valueToCount); SO, is the recursive part correct now?

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  • Java: Do something on event in SQL Database?

    - by wretrOvian
    Hello I'm building an application with distributed parts. Meaning, while one part (writer) maybe inserting, updating information to a database, the other part (reader) is reading off and acting on that information. Now, i wish to trigger an action event in the reader and reload information from the DB whenever i insert something from the writer. Is there a simple way about this? Would this be a good idea? : // READER while(true) { connect(); // reload info from DB executeQuery("select * from foo"); disconnect(); }

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  • How to gracefully handle the SIGKILL signal in Java

    - by Begui
    How do you handle clean up when the program receives a kill signal? For instance, there is an application I connect to that wants any third party app (my app) to send a finish command. What is the best say to send that finish command when my app has been destroyed with a kill -9?

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  • Java overloading and overriding

    - by Padmanabh
    We always say that method overloading is static polymorphism and overriding is runtime polymorphism. What exactly do we mean by static here? Is the call to a method resolved on compiling the code? So whats the difference between normal method call and calling a final method? Which one is linked at compile time?

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  • Improving performance for WRITE operation on Oracle DB in Java

    - by Lucky
    I've a typical scenario & need to understand best possible way to handle this, so here it goes - I'm developing a solution that will retrieve data from a remote SOAP based web service & will then push this data to an Oracle database on network. Also, this will be a scheduled task that will execute every 15 minutes. I've event queues on remote service that contains the INSERT/UPDATE/DELETE operations that have been done since last retrieval, & once I retrieve the events for last 15 minutes, it again add events for next retrieval. Now, its just pushing data to Oracle so all my interactions are INSERT & UPDATE statements. There are around 60 tables on Oracle with some of them having 100+ columns. Moreover, for every 15 minutes cycle there would be around 60-70 Inserts, 100+ Updates & 10-20 Deletes. This will be an executable jar file that will terminate after operation & will again start on next 15 minutes cycle. So, I need to understand how should I handle WRITE operations (best practices) to improve performance for this application as whole ? Current Test Code (on every cycle) - Connects to remote service to get events. Creates a connection with DB (single connection object). Identifies the type of operation (INSERT/UPDATE/DELETE) & table on which it is done. After above, calls the respective method based on type of operation & table. Uses Preparedstatement with positional parameters, & retrieves each column value from remote service & assigns that to statement parameters. Commits the statement & returns to get event class to process next event. Above is repeated till all the retrieved events are processed after which program closes & then starts on next cycle & everything repeats again. Thanks for help !

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  • How to build our own java custom layout

    - by nguyendat
    Please help me how to creat own custom layout, container, component, layout manager... Example: Containers and Layout Managers Create a window frame. Nest panels within a frame for better layout control. Create and display buttons in a panel. List two component attributes that are controlled by a layout manager. Set the layout manager for a container. Place components in a panel using BorderLayout, GridLayout, and FlowLayout. Name one advantage of each of the layout managers. Create panels with titles. i was search on google but can't find any that match my requirement Thanks for your help

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  • Splitting up input using regular expressions in Java

    - by Joe24
    I am making a program that lets a user input a chemical for example C9H11N02. When they enter that I want to split it up into pieces so I can have it like C9, H11, N, 02. When I have it like this I want to make changes to it so I can make it C10H12N203 and then put it back together. This is what I have done so far. using the regular expression I have used I can extract the integer value, but how would I go about get C10, H11 etc..? System.out.println("Enter Data"); Scanner k = new Scanner( System.in ); String input = k.nextLine(); String reg = "\\s\\s\\s"; String [] data; data = input.split( reg ); int m = Integer.parseInt( data[0] ); int n = Integer.parseInt( data[1] );

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  • singleton pattern in java- lazy Intialization

    - by flash
    public static MySingleton getInstance() { if (_instance==null) { synchronized (MySingleton.class) { _instance = new MySingleton(); } } return _instance; } 1.is there a flaw with the above implementation of the getInstance method? 2.What is the difference between the two implementations.? public static synchronized MySingleton getInstance() { if (_instance==null) { _instance = new MySingleton(); } return _instance; } I have seen a lot of answers on the singleton pattern in stackoverflow but the question I have posted is to know mainly difference of 'synchronize' at method and block level in this particular case.

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  • How to validate overlapping no in java

    - by anandhinaveen
    I Have dynamically render row. WE have fields like FROM TO. For eg: From TO 2 10, 2 3, 8 12 It cannot accept this combination row.. That means no number should be overlapping. For eg: From TO 2 10, 0 1, 11 12 This combination is allowed.the row may also increased. I need need to write a validation for this overlapping. Can any 1 help to solve this problem.

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  • Rotation in a Vector2d class in Java

    - by wanstein
    I've been working on this for one hour, just can't get it. I have a Vector2d class: public class Vector2d { public double x = 0.0; public double y = 0.0; .... } This vector class has a rotate() method which is causing me trouble. The first snippet seems to make the x and y values smaller and smaller. The second one works just fine! Am I missing something simple here? public void rotate(double n) { this.x = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); this.y = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); } This works: public void rotate(double n) { rx = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); ry = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); x = rx; y = ry; } I just can't spot any difference there

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  • Problem in arranging contents of Class in JAVA

    - by LuckySlevin
    Hi, I have some classes and I'm trying to fill the objects of this class. Here is what i've tried. (Question is at the below) public class Team { private String clubName; private String preName; private ArrayList<String> branches; public Team(String clubName, String preName) { this.clubName = clubName; this.preName = preName; branches = new ArrayList<String>(); } public Team() { // TODO Auto-generated constructor stub } public String getClubName() { return clubName; } public String getPreName() { return preName; } public ArrayList<String> getBranches() { return branches; } public void setClubName(String clubName) { this.clubName = clubName; } public void setPreName(String preName) { this.preName = preName; } public void setBranches(ArrayList<String> branches) { this.branches = branches; } } public class Branch { private ArrayList<Player> players = new ArrayList<Player>(); String brName; public Branch() {} public void setBr(String brName){this.brName = brName;} public String getBr(){return brName;} public ArrayList<Player> getPlayers() { return players; } public void setPlayers(ArrayList<Player> players) { this.players = players; } } //TEST CLASS public class test { /** * @param args * @throws IOException */ public static void main(String[] args) throws IOException { String a,b,c; String q = "q"; int brCount = 0, tCount = 0; BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); Team[] teams = new Team[30]; Branch[] myBranch = new Branch[30]; for(int z = 0 ; z <30 ;z++) { teams[z] = new Team(); myBranch[z] = new Branch(); } ArrayList<String> tmp = new ArrayList<String>(); int k = 0; int secim = Integer.parseInt(input.readLine()); while(secim != 0) { if(k!=0) secim = Integer.parseInt(input.readLine()); k++; switch(secim) { case 1 : brCount = 0; a = input.readLine(); teams[tCount].setClubName(a); b= input.readLine(); teams[tCount].setPreName(b); c = input.readLine(); while(c.equals(q) == false) { if(brCount != 0) {c = input.readLine();} if(c.equals(q)== false){ myBranch[brCount].brName = c; tmp.add(myBranch[brCount].brName); brCount++; } System.out.println(brCount); } teams[tCount].setBranches(tmp); for(int i=0;i<=tCount;i++ ){ System.out.print("a :" + teams[i].getClubName()+ " " + teams[i].getPreName()+ " "); System.out.println(teams[i].getBranches());} tCount++; break; case 2: String src = input.readLine();//LATERRRRRRRr } } } } The problem is one of my class elements. I have an arraylist as an element of a class. When i enter: AAA as preName BBB as clubName c d e as Branches Then as a second element www as preName GGG as clubName a b as branches The result is coming like: AAA BBB c,d,e,a,b GGG www c,d,e,a,b Which means ArrayList part of the class is putting it on and on. I tried to use clear() method but caused problems. Any ideas.

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  • replace \n and \r\n with <br /> in java

    - by Bala R
    This has been asked several times for several languages but I can't get it to work. I have a string like this String str = "This is a string.\nThis is a long string."; And I'm trying to replace the \n with <br /> using str = str.replaceAll("(\r\n|\n)", "<br />"); but the \n is not getting replaced. I tried to use this RegEx Tool to verify and I see the same result. The input string does not have a match for "(\r\n|\n)". What am i doing wrong ?

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  • Localized text in Java

    - by Eager Learner
    My requirement is to display localized text messages in a J2EE web application. I know J2EE provides very good support for this. My question is what is the practice followed to have the localized messages stored to be used by the application. If I want to display Japanese / Chinese kind of messages which are not like English like char sets how do we get that messages/text into the properties files or Database tables.

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  • ByteArrayOutputStream to PrintWriter (Java Servlet)

    - by Thomas
    Writing generated PDF (ByteArrayOutputStream) in a Servlet to PrintWriter. I am desperately looking for a way to write a generated PDF file to the response PrintWriter. Since a Filter up the hierarchy chain has already called response.getWriter() I can't get response.getOutputStream(). I do have a ByteArrayOutputStream where I generated the PDF into. Now all I need is a way to output the content of this ByteArrayOutputStream to the PrintWriter. If anyone could give me a helping hand would be very much appreciated!

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