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  • Interview question : What is the fastest way to generate prime number recursively ?

    - by hilal
    Generation of prime number is simple but what is the fastest way to find it and generate( prime numbers) it recursively ? Here is my solution. However, it is not the best way. I think it is O(N*sqrt(N)). Please correct me, if I am wrong. public static boolean isPrime(int n) { if (n < 2) { return false; } else if (n % 2 == 0 & n != 2) { return false; } else { return isPrime(n, (int) Math.sqrt(n)); } } private static boolean isPrime(int n, int i) { if (i < 2) { return true; } else if (n % i == 0) { return false; } else { return isPrime(n, --i); } } public static void generatePrimes(int n){ if(n < 2) { return ; } else if(isPrime(n)) { System.out.println(n); } generatePrimes(--n); } public static void main(String[] args) { generatePrimes(200); }

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  • Print unique ascii characters in eclipse console

    - by Shaded
    Hey guys, Kind of a strange question but... here it goes. Recently my application threw an IOException that the text only had a clubs symbol in it (like the suit in cards) I know this is probably because there was a number in there that was cast to a char and printed to the screen, and I've found where that might have happened. The only problem is, I can't recreate it in eclipse because the eclipse console doesn't want to print those characters for me. All I get are boxes. I figure this is an encoding issue or something but I need eclipse to print out those characters just like the windows console would. Is there a setting I can change to do this?

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  • problem with "select new Object ... join ... where"

    - by jacob
    Hi, I'm having a problem with an HQL query Three classes ClassOne is my BusinessObject public class ClassOne { private int id; private int status; private Set<ClassTwo> classTwos; + other fields/getters/setters/constructor etc } ClassTwo is referenced in a set of ClassOne and is kind of the history of an object of ClassOne public class ClassTwo { private int id; private int oldStatus; private int newStatus; private String message; //+ getters/setters/constructor etc } ClassThree is my DTO/VO with just one classTwo (not the whole history) public class ClassThree { private int id; private int status; private ClassTwo classTwo; public ClassThree(int pId, int pStatus, ClassTwo pClassTwo) { id=pId; status=pStatus; classTwo=pClassTwo; } //+ getters/setters etc } Now I'd like to create an HQL query like this: I'd like to get all objects of ClassThree with a certain status and if it exists the newest ClassTwo with a certain newStatus. For example: I'd like to get all the DTOs (ClassThree) of ClassOne whose status is now 1, but earlier in their history it has been 2 and I'd like to have the latest ClassTwo object which has 2 as newStatus. SELECT new ClassThree(c1.id, c1.status, c2) FROM ClassOne c1 LEFT JOIN c1.classtwos c2 (...) and (...) is where I don't know what to do, I'm not even sure if it's a join / join fetch Looked around and tried quite a lot already, but no clue. Especially with the join fetch I get some Hibernate errors like org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list. Fetching the BusinessObject like that is no problem SELECT distinct(c1) FROM ClassOne c1 LEFT OUTER JOIN FETCH c1.classtwos c2 and I get the ClassTwos as my field. Thanks in advance, Jacob P.S.: One thing might be important, ClassTwo has no reference to ClassOne!!

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  • Help in setting the setClientInfo with JPA

    - by enrique
    i am trying to set to jpa the new JDBC method which allows the application to be identified with a name it is the setClientInfo() and i could do it using pure JDBC using the lines Properties jdbcProperties = new Properties(); jdbcProperties.put("user", "system"); jdbcProperties.put("password", "sw01"); jdbcProperties.put("v$session.program", "Clients"); Connection connection = DriverManager.getConnection(url,jdbcProperties); However i have new requirements and i need to make it with JPA EclipseLink i have been googling and could not find something substantial on how to set this property out in JPA i guess it is by annotating something but i do not know what, i was trying to setting the persistence unit by putting the following in the persistence unit: <properties> <property name="toplink.ddl-generation" value="create-tables"/> <property name="v$session.program" value="Clients"/> </properties> but no lucky ...does somebody know how to do it or any idea...? thanks in advanced.-

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  • Blackberry Contacts Photo

    - by Farhan
    Hi, I am currently working on the Application named (Blackberry Contacts Sync) and i am stuck at this point that how i sync Contact's Image. Please tell me how to store images in Database(MySQL) and how to retrieve it.

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  • servlet connection to DB

    - by underW
    Initially, after reading books on the subject, I firmly believed that the algorithm for working with a database from a servlet is as follows: create a connection - connect to the database - form a request - send the request to the database - get the query results - process them - close connection - OK. Now, with a better understanding of the practical side, I realized that nobody does it that way, and everything happens through a connection pool according to the following algorithm: initialize the servlet - create a connection pool - a request comes from a user - take a free connection from the pool - form a request - send the request to the database - get the query results - process them - return the connection back to the pool - ok. Now I have this problem: We have 100 users, they are divided into 10 groups, each group has it's own username and password to connect to the database. Moreover, each group may have different rights to the database. How am I supposed to use a connection pool in this situation? If I understand correctly, a pool is nothing more than just a group of similar connections with a single login and password. And here I have 10 pairs of username / password. It looks like I cannot use the pool in this situation. What should I do?

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  • Android - Fill Layout with Buttons

    - by GuyNoir
    Just a quick question about how you would go about implementing this. I want there to be buttons at the bottom of the screen, but if the screen size is larger, more buttons would be added. For example, at a small screen size, there might be 4-5 buttons at the bottom, but if you ran it on a tablet or something similar, there would be maybe 20 buttons. Any suggestions? It can't scroll either, it just has to dynamically fill the layout with buttons. Thanks.

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  • Does a servlet knows the encoding of the sent form that specified using http-equiv?

    - by Daziplqa
    Does a servlet knows the encoding of the sent form that specified using http-equiv? When I specify an encoding of a POSTed form using http-equiv like that: <HTML> <head> <meta http-equiv='Content-Type' content='text/html; charset=gb2312'/> </head> <BODY > <form name="form" method="post" > <input type="text" name="v_rcvname" value="????"> </form> </BODY> </HTML> And then at the servlet I use the method, request.getCharacterEncoding() I got null ! So, Is there a way that I can tell the server that I am encoding the data in some char encoding??

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  • one more time about loop that doesn't work

    - by unit
    I have asked a couple of questions about this for loop: String[] book = new String [ISBN_NUM]; bookNum.replaceAll("-",""); if (bookNum.length()!=ISBN_NUM) throw new ISBNException ("ISBN "+ bookNum + " must be 10 characters"); for (int i=0;i<bookNum.length();i++) { if (Character.isDigit(bookNum.charAt(i))) book[j]=bookNum.charAt(i); //this is the problem right here j++; if (book[9].isNotDigit()|| book[9]!="x" || book[9]!="X") throw new ISBNException ("ISBN " + bookNum + " must contain all digits" + "or 'X' in the last position"); } which will not compile. An answer I had from the other question I asked told me that the line where the error occurs is wrong in that bookNum.charAt(i) is an (immutable) string, and I can't get the values into a book array that way. What I need to do on my assignment is check an ISBN number (bookNum) to see that it is all numbers, except the last digit can be an 'x' (valid ISBN). Is this the best way to do it? If so, what the hell am I doing wrong? If not, what method would be a better one to use?

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  • "Overriding" instance variables in subtype: Possible risks?

    - by sebastiangeiger
    Say I had a class SuperClass and two subclasses SubClassA and SubClassB that inherit from SuperClass. abstract class SuperClass{ ... List someList; ... } class SubClassA extends SuperClass{ ... List<String> someList; ... } class SubClassB extends SuperClass{ ... List<Integer> someList; ... } That way it is convenient because I can get someList.size() in Superclass and have Typesafety in the Subclasses. The problem is that it does not "feel" right, can you think of potential hazards this apporach has that I am not aware of?

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  • Ignoring all line feeds in a FreeMarker template

    - by Will
    I'm trying out FreeMarker, not for a web application but to generate text within a desktop application. I'd like to get the text without any linefeeds, however it always appends a linefeed. For example, this would produce "blah blah\n" <#if docType=1> blah blah <#if docType=2> more blah <#/if> Any ideas? Bunching it all into one line works, but is horrible. Thanks.

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  • How to see "anti if" movement and its gaol?

    - by Vijay Shanker
    I have a developer for last 3 years, have been using if-else or if-else if statements a lot in my programing habit. And today, I found This link. One obvious sample i put here public void doSomthing(String target, String object){ //validate requests if(target != null && target.trim().length() < 1){ //invalid request; } //further logic } Now, I have seen this sort of check all over the places, libraries. So, I wanted to have a discussion about the worthiness of such a movement. Please let me know your views.

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  • Does allocation speed depend on the garbage collector being used?

    - by jkff
    My app is allocating a ton of objects (1mln per second; most objects are byte arrays of size ~80-100 and strings of the same size) and I think it might be the source of its poor performance. The app's working set is only tens of megabytes. Profiling the app shows that GC time is negligibly small. However, I suspect that perhaps the allocation procedure depends on which GC is being used, and some settings might make allocation faster or perhaps make a positive influence on cache hit rate, etc. Is that so? Or is allocation performance independent on GC settings under the assumption that garbage collection itself takes little time?

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  • javax.activation.DataSource size question

    - by folone
    How do I get the amount of physical memory, consumed by the DataSource (specifically — ByteArrayDataSource)? I use ByteArrayDataSource (byte[] bytes, String type) constructor, where I get bytes like this: String str = "test"; byte[] bytes = str.getBytes(); Would that be str.length() in bytes? Any other ideas?

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  • Compilation Error related

    - by aparna
    Given: 11. public static void test(String str) { 12. int check = 4; 13. if (check = str.length()) { 14. System.out.print(str.charAt(check -= 1) +", "); 15. } else { 16. System.out.print(str.charAt(0) + ", "); 17. } 18. } and the invocation: 21. test("four"); 22. test("tee"); 23. test("to"); What is the result? A. r, t, t, B. r, e, o, C. Compilation fails. D. An exception is thrown at runtime. Answer: C Can you explain why the compilation fails please?

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  • frame variable cannot be found

    - by Umzz Mo
    I am making 3 board games, and I have started my coding off in one class. Now that i wanted to move around it is giving me problems. In my view class I just want to have the main frame where users can pick from the games. And in the other views, i.e the childrens of view class i want to have the interface for the actual games. Now that the Jframe frame = new frame was created in the parent class, it cannot find the variable frame in the children classes.

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  • How to stop rendering invisible faces

    - by TheMorfeus
    I am making a voxel-based game, and for needs of it, i am creating a block rendering engine. Point is, that i need to generate lots of cubes. Every time i render more than 16x16x16 chunk of theese blocks, my FPS is dropped down hardly, because it renders all 6 faces of all of theese cubes. THat's 24 576 quads, and i dont want that. So, my question is, How to stop rendering vertices(or quads) that are not visible, and therefore increase performance of my game? Here is class for rendering of a block: public void renderBlock(int posx, int posy, int posz) { try{ //t.bind(); glEnable(GL_CULL_FACE); glCullFace(GL_BACK);// or even GL_FRONT_AND_BACK */); glPushMatrix(); GL11.glTranslatef((2*posx+0.5f),(2*posy+0.5f),(2*posz+0.5f)); // Move Right 1.5 Units And Into The Screen 6.0 GL11.glRotatef(rquad,1.0f,1.0f,1.0f); glBegin(GL_QUADS); // Draw A Quad GL11.glColor3f(0.5f, 0.4f, 0.4f); // Set The Color To Green GL11.glTexCoord2f(0,0); GL11.glVertex3f( 1f, 1f,-1f); // Top Right Of The Quad (Top) GL11.glTexCoord2f(1,0); GL11.glVertex3f(-1f, 1f,-1f); // Top Left Of The Quad (Top) GL11.glTexCoord2f(1,1); GL11.glVertex3f(-1f, 1f, 1f); // Bottom Left Of The Quad (Top) GL11.glTexCoord2f(0,1); GL11.glVertex3f( 1f, 1f, 1f); // Bottom Right Of The Quad (Top) //GL11.glColor3f(1.2f,0.5f,0.9f); // Set The Color To Orange GL11.glTexCoord2f(0,0); GL11.glVertex3f( 1f,-1f, 1f); // Top Right Of The Quad (Bottom) GL11.glTexCoord2f(0,1); GL11.glVertex3f(-1f,-1f, 1f); // Top Left Of The Quad (Bottom) GL11.glTexCoord2f(1,1); GL11.glVertex3f(-1f,-1f,-1f); // Bottom Left Of The Quad (Bottom) GL11.glTexCoord2f(1,0); GL11.glVertex3f( 1f,-1f,-1f); // Bottom Right Of The Quad (Bottom) //GL11.glColor3f(1.0f,0.0f,0.0f); // Set The Color To Red GL11.glTexCoord2f(0,0); GL11.glVertex3f( 1f, 1f, 1f); // Top Right Of The Quad (Front) GL11.glTexCoord2f(1,0); GL11.glVertex3f(-1f, 1f, 1f); // Top Left Of The Quad (Front) GL11.glTexCoord2f(1,1); GL11.glVertex3f(-1f,-1f, 1f); // Bottom Left Of The Quad (Front) GL11.glTexCoord2f(0,1); GL11.glVertex3f( 1f,-1f, 1f); // Bottom Right Of The Quad (Front) //GL11.glColor3f(1f,0.5f,0.0f); // Set The Color To Yellow GL11.glTexCoord2f(0,0); GL11.glVertex3f( 1f,-1f,-1f); // Bottom Left Of The Quad (Back) GL11.glTexCoord2f(1,0); GL11.glVertex3f(-1f,-1f,-1f); // Bottom Right Of The Quad (Back) GL11.glTexCoord2f(1,1); GL11.glVertex3f(-1f, 1f,-1f); // Top Right Of The Quad (Back) GL11.glTexCoord2f(0,1); GL11.glVertex3f( 1f, 1f,-1f); // Top Left Of The Quad (Back) //GL11.glColor3f(0.0f,0.0f,0.3f); // Set The Color To Blue GL11.glTexCoord2f(0,1); GL11.glVertex3f(-1f, 1f, 1f); // Top Right Of The Quad (Left) GL11.glTexCoord2f(1,1); GL11.glVertex3f(-1f, 1f,-1f); // Top Left Of The Quad (Left) GL11.glTexCoord2f(1,0); GL11.glVertex3f(-1f,-1f,-1f); // Bottom Left Of The Quad (Left) GL11.glTexCoord2f(0,0); GL11.glVertex3f(-1f,-1f, 1f); // Bottom Right Of The Quad (Left) //GL11.glColor3f(0.5f,0.0f,0.5f); // Set The Color To Violet GL11.glTexCoord2f(0,0); GL11.glVertex3f( 1f, 1f,-1f); // Top Right Of The Quad (Right) GL11.glTexCoord2f(1,0); GL11.glVertex3f( 1f, 1f, 1f); // Top Left Of The Quad (Right) GL11.glTexCoord2f(1,1); GL11.glVertex3f( 1f,-1f, 1f); // Bottom Left Of The Quad (Right) GL11.glTexCoord2f(0,1); GL11.glVertex3f( 1f,-1f,-1f); // Bottom Right Of The Quad (Right) //rquad+=0.0001f; glEnd(); glPopMatrix(); }catch(NullPointerException t){t.printStackTrace(); System.out.println("rendering block failed");} } Here is code that renders them: private void render() { GL11.glClear(GL11.GL_COLOR_BUFFER_BIT|GL11.GL_DEPTH_BUFFER_BIT); for(int y=0; y<32; y++){ for(int x=0; x<16; x++){ for(int z=0; z<16; z++) { b.renderBlock(x, y, z); } } } }

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  • How can I close my software in a save way?

    - by Roman
    Up to now I used my application as a stand alone product. So, when user pressed "Stop" button I called System.exit(0); and it was fine. Now my application will be called (in a programmatic way) from another program. So, I afraid that System.exit(0); will kill not only my process but also the external software which started my program. So, what is the correct way to shutdown my application if a corresponding request from an external software is received? My application is an GUI application. So, I want to close the window but I also want to close all processes performed by my program. ADDED: To be more specific, I want to close all threads started by my program. My program does not start any OS process or any other program.

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