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• Teacher confused about MVC?

  - by Gideon

  I have an assignment to create a game in java using MVC as a pattern. The thing is that stuff I read about MVC aren't really what the teacher is telling me. What I read is that the Model are the information objects, they are manipulated by the controllers. So in a game the controller mutates the placement of the objects and check if there is any collision etc. What my teacher told me is that I should put everything that is universal to the platform in the models and the controllers should only tell the model which input is given. That means the game loop will be in a model class, but also collision checks etc. So what I get from his story is that the View is the screen, the Controller is the unput handeler, and the Model is the rest. Can someone point me in the right direction?

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• PgJDBC: "no suitable driver found" when following tutorial, why?

  - by Celeritas

  I'm writing a Java program that queries a PostgreSQL database. I'm following this example and have trouble here: connection = DriverManager.getConnection( "jdbc:postgresql://127.0.0.1:5432/testdb", "mkyong", "123456"); According to the JavaDoc for DriverManager the first string is "a database url of the form jdbc:subprotocol:subname. When I connect to the server I type in psql -h dataserv.abc.company.com -d app -U emp24 and give the password qwe123 (for example sake). What should the first argument of getConnection be? I've tried connection = DriverManager.getConnection( "jdbc:postgresql://dataserv.abc.company.com", "emp24", "qwe123"); and get the run time error: no suitable driver found. I've download JDBC4 Postgresql Driver, Version 9.2-1000.

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• How to start an Open Source Software development

  - by harigm

  I have an idea to start a Open Source Software using Java and PHP, I am so sure that software will help many individuals in their daily routine. Can Any one suggest me how to start the process ? Do we need to register some where and submit our idea for an approval before we start development? Any license that we need to get? How to invite the people for the open source development community, if they are interested? If any people who contributes Do we need to get any agreement signed off? once the Open Source product is stabilized who will have the ownership?

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• help implementing All Nearest Smaller Values algorithm

  - by davit-datuashvili

  http://en.wikipedia.org/wiki/All_nearest_smaller_values this is site of the problem and here is my code but i have some trouble to implement it import java.util.*; public class stack{ public static void main(String[]args){ int x[]=new int[]{ 0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15 }; Stack<Integer> st=new Stack<Integer>(); for (int a:x){ while (!st.empty() && st.pop()>=a){ System.out.println( st.pop()); if (st.empty()){ break; } else{ st.push(a); } } } } } and here is pseudo code from site S = new empty stack data structure for x in the input sequence: while S is nonempty and the top element of S is greater than or equal to x: pop S if S is empty: x has no preceding smaller value else: the nearest smaller value to x is the top element of S push x onto S

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• Ideally How many connections I have to open ?

  - by ranjith-kumar-u

  Hi All, Recently I attended interview in java, the interviewer asked a question like below: I have a request which go throgh A,B,C modules and response go back throgh A , in module A I need to talk to database and again in module C I need to talk to database, so in this situation how many connections you will open and where do you close those connections? My Answer: I said that in module A I will open a connection and I will close it then and there, then control go to module B then module C, in module C again I will open one more connection and i will close it again. then he asked me again another question I want to open one connection per one request processing, how can i do this?

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• Google app engine sessions now supported???

  - by user246114

  Hi, I thought google app engine did not support sessions (last time I checked was a few months ago). Now I was searching again for it and saw this: http://code.google.com/appengine/docs/java/config/appconfig.html#Enabling_Sessions says it supports: javax.servlet.http.HttpSession does this mean we have servlet session support now? If so, does anyone have an example of using this? I wanted to create my own User class and support user login and session management (I know app engine already supports this for google users, but wanted my own users for various requirements) Thanks!

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• Behavior of nested finally in Exceptions

  - by kuriouscoder

  Hello: Today at work, I had to review a code snippet that looks similar to this mock example. package test; import java.io.IOException; import org.apache.log4j.Logger; public class ExceptionTester { public static Logger logger = Logger.getLogger(ExceptionTester.class); public void test() throws IOException { new IOException(); } public static void main(String[] args) { ExceptionTester comparator = new ExceptionTester(); try { try { comparator.test(); } finally { System.out.println("Finally 1"); } } catch(IOException ex) { logger.error("Exception happened" ex); // also close opened resources } System.out.println("Exiting out of the program"); } } It's printing the following output.I expected an compile error since the inner try did not have a catch block. Finally 1 Exiting out of the program I do not understand why IOException is caught by the outer catch block. I would appreciate if anyone can explain this, especially by citing stack unwinding process

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• Is it a good idea to use only a key to encrypt an entire (small) filesystem?

  - by Fernando Miguélez

  This question comes as part of my doubts presented on a broader question about ideas implementing a small encrypted filesystem on Java Mobile phones (J2ME, BlackBerry, Android). Provided the litte feedback received, considering the density of the question, I decided to divide those doubts into small questions. So to sum up I plan to "create" an encrypted filesystem for for mobile phones (with the help of BoucyCastle or a subset of JCE), providing an API that let access to them in a transparent way. Encryption would be carried out on a file basis (not blocks). My question is this: Is it a good idea to use only a simmetric key (maybe AES-256) to encrypt all the files (they wouldn't be that many, maybe tens of them) and store this key in a keystore (protected by a pin) or would you rather encrypt each file with an on-the-fly generated key stored alongside each file, encrypting that key with the "master" key stored on the keystore? What are the benefits/drawbacks of each approach?

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• Mapping tables from an existing database to an object -- is Hibernate suited?

  - by Bernhard V

  Hello! I've got some tables in an existing database and I want to map them to a Java object. Actually it's one table that contains the main information an some other tables that reference to such a table entry with a foreign key. I don't want to store objects in the database, I only want to read from it. The program should not be allowed to apply any changes to the underlying database. Currently I read from the database with 5 JDBC sql queries and set the results then on an object. I'm now looking for a less code intensive way. Another goal is the learning aspect. Is Hibernate suitable for this task, or is there another ORM framework that better fits my requirement?

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• Full GC real time is much more that user+sys times

  - by Stas

  Hi. We have a Web Java based application running on JBoss with allowed maximum heap size of about 1.2 GB (total machine physical memory is 2 GB). At some point the application stops responding (to clients) for several minutes. After some analysis we found out that the culprit is the Full GC. Here's an excerpt from the verbose GC log: 74477.402: [Full GC [PSYoungGen: 3648K-0K(332160K)] [PSOldGen: 778476K-589497K(819200K)] 782124K-589497K(1151360K) [PSPermGen: 102671K-102671K(171328K)], 646.1546860 secs] [Times: user=3.84 sys=3.72, real=646.17 secs] What I don't understand is how is it possible that the real time spent on Full GC is about 11 minutes (646 seconds), while user+sys times are just 7.5 seconds. 7.5 seconds sound to me much more logical time to spend for cleaning <200 MB from the old generation. Where does all the other time go? Thanks a lot.

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• How to search for duplicate values in a huge text file having around Half Million records

  - by Shibu

  I have an input txt file which has data in the form of records (each row is a record and represents more or less like a DB table) and I need to find for duplicate values. For example: Rec1: ACCOUNT_NBR_1*NAME_1*VALUE_1 Rec2: ACCOUNT_NBR_2*NAME_2*VALUE_2 Rec3: ACCOUNT_NBR_1*NAME_3*VALUE_3 In the above set, the Rec1 and Rec2 are considered to be duplicates as the ACCOUNT NUMBERS are same(ACCOUNT_NBR1). Note: The input file shown above is a delimiter type file (the delimiter being *) however the file type can also be a fixed length file where each column starts and ends with a specified positions. I am currently doing this with the following logic: Loop thru each ACCOUNT NUMBER Loop thru each line of the txt file and record and check if this is repeated. If repeated record the same in a hashtable. End End And I am using 'Pattern' & 'BufferedReader' java API's to perform the above task. But since it is taking a long time, I would like to know a better way of handling it. Thanks, Shibu

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• Running a method after the constructor of any derived class

  - by Alexey Romanov

  Let's say I have a Java class abstract class Base { abstract void init(); ... } and I know every derived class will have to call init() after it's constructed. I could, of course, simply call it in the derived classes' constructors: class Derived1 extends Base { Derived1() { ... init(); } } class Derived2 extends Base { Derived2() { ... init(); } } but this breaks "don't repeat yourself" principle rather badly (and there are going to be many subclasses of Base). Of course, the init() call can't go into the Base() constructor, since it would be executed too early. Any ideas how to bypass this problem? I would be quite happy to see a Scala solution, too.

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• How to set the component size with GridLayout? Is there a better way?

  - by Blackbam

  Hello guys, I am working on a larger GUI with Java and I am becoming angry on Layout Managers. I have a "Settings-Panel" with a variable number of JComponents in it (Labels, Buttons, JSpinners, JSliders,...). I just want the following: JLabel <- JComponent JLabel <- JComponent JLabel <- JComponent ... My Panel has a size of 500px, so that there is enough space for a lot of components. Unfortunatly the GridLayout always stretches the size of the Components to the whole Panel, even if I set a MaximumSize for every component. It looks stupid if there are only two buttons each with a height of 250px. I tried flow Layout, but i cannot figure out a way to make new lines properly. I tried BoxLayout.Y_AXIS, but the Components are always centered, and Label and Component are not in the same line. Does anybody know a good and short way with LayoutManagers to handle this properly?

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• Checking for 2 exepcted values in Junit

  - by Swift-Tuttle

  Hi, I have a java program which throws an exception with 2 different messages for 2 different scenarios and I want the Junit test case to check for equality for both of these messages. As an example - public void amethod() { // do some processing if(scenario1 == true) { throw new MySystemException("An error occured due to case 1 being incorrect."); } else if(scenario2 == true) { throw new MySystemException("An error occured as case 2 could not be found"); } } Now the JUnit for this would be something like- public void testAMethod() { // do something assertEquals("Expected", "Actual"); } As I understand, in this above example, if I use the Scenario1 exception message the junit will fail when an exception is thrown for Scenario2 and vice versa. I would like to know if there is any other way provided in Junit by which I can use this one test method and check for both the messages for the test to pass? Something like an OR, if possible to provide the "Expected" value with both these expected message. I hope my query is clear enough. Thanks

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• Access of private field of another object in copy constructors - Really a problem?

  - by DR

  In my Java application I have some copy-constructors like this public MyClass(MyClass src) { this.field1 = src.field1; this.field2 = src.field2; this.field3 = src.field3; ... } Now Netbeans 6.9 warns about this and I wonder what is wrong with this code? My concerns: Using the getters might introduce unwanted side-effects. The new object might no longer be considered a copy of the original. If it is recommended using the getters, wouldn't it be more consistent if one would use setters for the new instance as well?

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• Measuring the time to create and destroy a simple object

  - by portoalet

  From Effective Java 2nd Edition Item 7: Avoid Finalizers "Oh, and one more thing: there is a severe performance penalty for using finalizers. On my machine, the time to create and destroy a simple object is about 5.6 ns. Adding a finalizer increases the time to 2,400 ns. In other words, it is about 430 times slower to create and destroy objects with finalizers." How can one measure the time to create and destroy an object? Do you just do: long start = System.nanoTime(); SimpleObject simpleObj = new SimpleObject(); simpleObj.finalize(); long end = System.nanoTime(); long time = end - start;

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• Persisting non-entity class that extends an entity (jpa) - example?

  - by Michal Minicki

  The JPA tutorial states that one can have a non-entity that extends entity class: Entities may extend both entity and non-entity classes, and non-entity classes may extend entity classes. - http://java.sun.com/javaee/5/docs/tutorial/doc/bnbqa.html Is it possible to persist such structure? I want to do this: @Entity abstract class Test { ... } class FirstConcreteTest extends Test { ... } // Non-ntity class SecondConcreteTest extends Test { ... } // Non-entity Test test = new FirstConcreteTest(); em.persist(test); What I would like it to do is to persist all fields mapped on abstract Test to a common database table for all concrete classes (first and second), leaving all fields of first and second test class unpersisted (these can contain stuff like EJBs, jdbc pools, etc). And a bonus question. Is it possible to persist abstract property too? @Entity abstract class Test { @Column @Access(AccessType.PROPERTY) abstract public String getName(); } class SecondConcreteTest extends Test { public String getName() { return "Second Concrete Test"; } }

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• Hibernate, select by id or unique column

  - by Nican

  I am using hibernate for Java, and I want to be able to select users by id or by name from the database. Nice thing about Hibernate is that it caches the result by id, but I seem to be unable to make it cache by name. static Session openSession = Factory.openSession(); public static User GetUser(int Id) { return (User) openSession.get(User.class, new Integer(Id)); } public static User GetUser( String Name ){ return (User) openSession.createCriteria( User.class ). add( Restrictions.eq("username", Name) ). uniqueResult(); } If I use GetUser(1) many times, hibernate will only show that it executed the first time. But every time I use GetUser("user1"), hibernate shows that it is executing a new query to database. What would be the best way to have the string identifier be cached also?

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• input in search box programmatically

  - by Sahil Manchanda

  I'm making a Java program where I programmatically insert data into search field of a website and make submit event programmatically . after submission a new website is opened.. i know i can read data using URLCONNECTION. Eg if website name is www.pqr.net/index.php after I make search submission I'm redirected to that page. eg. www.pqr.net/ind2.php how to get the url of page where I'm redirected because I want to read the contents of that page , unless I don't know the url of the page where I'm redirected , I can't read the contents

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• Apache HTTPClient returns an empty page

  - by mariosangiorgio

  Hi, I am using the Apache HTTPClient for Java and I'm facing a really strange issue. Sometimes when I try to get a dynamically generated page it returns its actual content, but other times (with another parameter) all I get is a short sequence of \t,\r and \n. How could I track what's going on on the different cases in order to find where is the bug? My usage of the library is pretty straightforward, all I do is this few calls on an initialized HTTPClient object: String content = "/pageIwant.jsp?parameter=10101010"; HttpGet request = new HttpGet(content); HttpResponse response = client.execute(targetHost, request); HttpEntity entity = response.getEntity(); String page = EntityUtils.toString(entity);

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• any ways saving user information without db

  - by hguser

  Hi: I have a application which require login,but the number of user who use the application is no more than 40. And In the application,I get some data from the sql server database where I juse have read permission,also I can not create a table in the db for user validate. ALso I do not think it is a good idea to create a user table in other database on another machine.(for example,I can create a user table in the mysql another machine,but is it desireable just for user validating)? Now I just save the user info in a .properties file,any other good idea? BTW,the programe language used in my application is java.

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• Parameter attributes in c#

  - by ng

  How can I do the following with c# attributes. Below is a snippet of Java that annotates parameters in a constructor. public class Factory { private final String name; private final String value; public Factory(@Inject("name") String name, @Inject("value") String value) { this.name = name; this.value = value; } } From looking at c# annotations it does not look like I can annotate parameters. Is this possible?

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• How to get the action from the HttpServlet request to dispatch to multiple pages

  - by JFB

  I am using the Page Controller pattern. How could I use the same controller for two different pages by detecting the request action and then dispatching according to the result? Here is my code: account.jsp <form name="input" action="<%=request.getContextPath() %>/edit" method="get"> <input type="submit" value="Modifier" /> </form> Account Servlet public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("received HTTP GET"); String action = request.getParameter("action"); if (action == null) { // the account page dispatch(request, response, "/account"); } else if (action == "/edit") { // the popup edit page dispatch(request, response, "/edit"); } protected void dispatch(HttpServletRequest request, HttpServletResponse response, String page) throws javax.servlet.ServletException, java.io.IOException { RequestDispatcher dispatcher = getServletContext() .getRequestDispatcher(page); dispatcher.forward(request, response); } }

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• Hibernate and Child Objects (add versus clear)

  - by tyndall

  Lets say I have domain model with Automobile and Wheels. Wheels is a List of Wheels Wheels has a many-to-one relationship to Automobile. If I get an object back from Hibernate and it has 4 wheels. I take that object remove the 4 wheels and add 4. And then Save. If I ask Hibernate for the object again and it returns an auto with 8 wheels... what are we doing wrong? I don't have access to the source for a few days but want to give our Java devs a push in the right direction. Thanks.

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• Generics limitation, or lack of skillz ?

  - by Two Shoes

  I want to define the following class as such: public class CollectionAttribute<E extends Collection<T>> { private String name; private E value; public CollectionAttribute(String name, E value) { this.name = name; this.value = value; } public E getValue() { return value; } public void addValue(T value) { value.add(T); } } This won't compile (cannot resolve symbol T). If I replace the class declaration with the following: public class CollectionAttribute<E extends Collection<?>> Then I can't reference the parametrized type of the collection. Am I missing something or have I reached a limitation with generics in Java ?

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