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• reversing keys/values - create new instance of HashMap

  - by stck777

  I’ve got an existing instance of HashMap simply called sale (it is Map) I use it to log customers and items history. Is there a way to create a new instance of HashMap, that effectively reverses this usage? i.e will show each item purchased as a unique key and the corresponding value as a String set of the customers that have purchased that product. I suspect there is a simple process using keySet() in some way to iterate over the sales map but I just can’t see how to do this. Any help would be much appreciated.

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• Stuck at being unable to print a substring no more than 4679 characters

  - by Newcoder

  I have a program that does string manipulation on very large strings (around 100K). The first step in my program is to cleanup the input string so that it only contains certain characters. Here is my method for this cleanup: public static String analyzeString (String input) { String output = null; output = input.replaceAll("[-+.^:,]",""); output = output.replaceAll("(\\r|\\n)", ""); output = output.toUpperCase(); output = output.replaceAll("[^XYZ]", ""); return output; } When i print my 'input' string of length 97498, it prints successfully. My output string after cleanup is of length 94788. I can print the size using output.length() but when I try to print this in Eclipse, output is empty and i can see in eclipse output console header. Since this is not my final program, so I ignored this and proceeded to next method that does pattern matching on this 'cleaned-up' string. Here is code for pattern matching: public static List<Integer> getIntervals(String input, String regex) { List<Integer> output = new ArrayList<Integer> (); // Do pattern matching Pattern p1 = Pattern.compile(regex); Matcher m1 = p1.matcher(input); // If match found while (m1.find()) { output.add(m1.start()); output.add(m1.end()); } return output; } Based on this program, i identify the start and end intervals of my pattern match as 12351 and 87314. I tried to print this match as output.substring(12351, 87314) and only get blank output. Numerous hit and trial runs resulted in the conclusion that biggest substring that i can print is of length 4679. If i try 4680, i again get blank input. My confusion is that if i was able to print original string (97498) length, why i couldnt print the cleaned-up string (length 94788) or the substring (length 4679). Is it due to regular expression implementation which may be causing some memory issues and my system is not able to handle that? I have 4GB installed memory.

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• use of system.exit(0)

  - by Warrior

  public class WrapperTest { static { print(10); } static void print(int x) { System.out.println(x); System.exit(0); } } In the above code System.exit(0) is used to stop the program. What argument does that method take? Why do we gave it as 0. Can anyone explain the concept?Thanks.

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• Create a triangle out of stars using only recursion

  - by Ramblingwood

  I need to to write a method that is called like printTriangle(5);. We need to create an iterative method and a recursive method (without ANY iteration). The output needs to look like this: * ** *** **** ***** This code works with the iterative but I can't adapt it to be recursive. public void printTriangle (int count) { int line = 1; while(line <= count) { for(int x = 1; x <= line; x++) { System.out.print("*"); } System.out.print("\n"); line++; } } I should not that you cannot use any class level variables or any external methods. Thanks.

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• Why does Hibernate 2nd level cache only cache queries within a session?

  - by Synesso

  Using a named query in our application and with ehcache as the provider, it seems that the query results are tied to the session within the cache. Any attempt to access the value from the cache for a second time results in a LazyInitializationException We have set lazy = true for the following mapping because this object is also used by another part of the system which does not require the reference... and we want to keep it lean. <class name="domain.ReferenceAdPoint" table="ad_point" mutable="false" lazy="false"> <cache usage="read-only"/> <id name="code" type="long" column="ad_point_id"> <generator class="assigned" /> </id> <property name="name" column="ad_point_description" type="string"/> <set name="synonyms" table="ad_point_synonym" cascade="all-delete-orphan" lazy="true"> <cache usage="read-only"/> <key column="ad_point_id" /> <element type="string" column="synonym_description" /> </set> </class> <query name="find.adpoints.by.heading">from ReferenceAdPoint adpoint left outer join fetch adpoint.synonyms where adpoint.adPointField.headingCode = ?</query> Here's a snippet from our hibernate.cfg.xml <property name="hibernate.cache.provider_class">net.sf.ehcache.hibernate.SingletonEhCacheProvider</property> <property name="hibernate.cache.use_query_cache">true</property> It doesn't seem to make sense that the cache would be constrained to the session. Why are the cached queries not usable outside of the (relatively short-lived) sessions?

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• Configure autocomplete in intellij with hamcrest and mockito dsl

  - by sgargan

  I'm wondering if its possible to configure Intellij's smart insert to suggest hamcrest and mockito dsl idioms when in test classes. Really I'm looking for something like eclipse's 'static favorites', so that when I hit ctrl + space or ctrl +shift +space the idioms are present. In general is it possible to configure autocomplete/smart insert or the suggestions balloon for that matter. I've looked through the settings without much luck but could easily have overlooked something.

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• about the usage of mudolus operator

  - by matin1234

  Hi this a part of code for Quick Sort algorithm but realy I do not know that why it uses rand() %n please help me thanks Swap(V,0,rand() %n) // move pivot elem to V[0]

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• Apache Wicket exposes attributes

  - by Luke

  I just tried the Apache Wicket "Hello, world" application and I noticed that in the rendered HTML output, Wicket is exposing it's internal attributes. This is what the rendered HTML looks like in the 'view source' of the browser: <html> <body> <span wicket:id="message" id="message">Hello World!</span> </body> </html> How do I get rid of the wicket:id="message" attribute in the rendered HTML output?

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• org.apache.commons.httpclient.NameValuePair in post method

  - by pushkins

  I'm writing some code like : PostMethod p = new PostMethod(someurl); ... NameValuePair[] data = { new NameValuePair("name1", "somevalue1"), new NameValuePair("var[3][1]", "10") }; try { hc.executeMethod(p); } ... And that's what I get, when I look at my post in Wireshark: POST /someurl HTTP/1.1 ... type=var&ship%5B3%5D%5B1%5D=10 %5B means [, %5D- ] So the problem is how I can get square brackets in my post?

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• What's the purpose of the maxPostSize for Tomcat's HTTP Connector?

  - by Bytecode Ninja

  According to Tomcat docs: The maximum size in bytes of the POST which will be handled by the container FORM URL parameter parsing. The limit can be disabled by setting this attribute to a value less than or equal to 0. If not specified, this attribute is set to 2097152 (2 megabytes). But what's "the container FORM URL parameter parsing"? Any ideas what is the purpose of "maxPostSize"? Thanks in advance.

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• lucene get matched terms in query

  - by iamrohitbanga

  what is the best way to find out which terms in a query matched against a given document returned as a hit in lucene? I have tried a weird method involving hit highlighting package in lucene contrib and also a method that searches for every word in the query against the top most document ("docId: xy AND description: each_word_in_query"). Do not get satisfactory results? hit highlighting does not report some of the words that matched for a document other than the first one. i am not sure if the second approach is the best alternative.

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• Weak hashmap with weak references to the values?

  - by Razor Storm

  I am building an android app where each entity has a bitmap that represents its sprite. However, each entity can be be duplicated (there might be 3 copies of entity asdf for example). One approach is to load all the sprites upfront, and then put the correct sprite in the constructors of the entities. However, I want to decode the bitmaps lazily, so that the constructors of the entities will decode the bitmaps. The only problem with this is that duplicated entities will load the same bitmap twice, using 2x the memory (Or n times if the entity is created n times). To fix this, I built a SingularBitmapFactory that will store a decoded Bitmap into a hash, and if the same bitmap is asked for again, will simply return the previously hashed one instead of building a new one. Problem with this, though, is that the factory holds a copy of all bitmaps, and so won't ever get garbage collected. What's the best way to switch the hashmap to one with weakly referenced values? In otherwords, I want a structure where the values won't be GC'd if any other object holds a reference to it, but as long as no other objects refers it, then it can be GC'd.

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• Calculated group-by fields in MongoDB

  - by Navin Viswanath

  For this example from the MongoDB documentation, how do I write the query using MongoTemplate? db.sales.aggregate( [ { $group : { _id : { month: { $month: "$date" }, day: { $dayOfMonth: "$date" }, year: { $year: "$date" } }, totalPrice: { $sum: { $multiply: [ "$price", "$quantity" ] } }, averageQuantity: { $avg: "$quantity" }, count: { $sum: 1 } } } ] ) Or in general, how do I group by a calculated field?

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• Who creates beans in a spring web appplication?

  - by user319694

  I know that in a standalone application I create one of the application context instances which in turn creates the beans from conf files. But I can not see any such code in dispatched servlet. How then are the beans created in a web application?

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• gae xmpp outbound service

  - by cometta

  currently i create xmppservlet like below public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException { JID jid = new JID("[email protected]"); Message msg = new MessageBuilder() .withRecipientJids(jid) .withBody("hi Hello i'm a fancy GAE app, how are you?") .build(); XMPPService xmpp = XMPPServiceFactory.getXMPPService(); SendResponse status = xmpp.sendMessage(msg); } by doing this, from [email protected], i need to send a message to [email protected] only, will [email protected] send out the message back to [email protected]. Is there anyway to programatically send out xmpp message without having [email protected] to initial chat window with [email protected] and send the first message? This should be consider outbound-service right? how to do this?

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• How can I make properties files mandatory in Spring?

  - by Paulo Guedes

  I have an ApplicationContext.xml file with the following node: <context:property-placeholder location="classpath:hibernate.properties, classpath:pathConfiguration.properties" /> It specifies that both properties files will be used by my application. But if one of these files does not exist, no error ir thrown. How can I throw an exception for any of these files? They should me mandatory.

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• Setting jvmargs in log4j.properties file

  - by Thomas

  Hey This is a bit of a weird request but I am trying to set some jvmargs in the log4j.properties file. At present I use ant to for example set some args.... jvmarg value="-Dmail.smtp.socketFactory.port=465" ... but it would be great to group a few of these logging relevant arguments into the .properties file. Does anyone know how to do this? Thanks in advance!

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• How do I remove implementing types from GWT’s Serialization Policy?

  - by Bluu

  The opposite of this question: http://stackoverflow.com/questions/138099/how-do-i-add-a-type-to-gwts-serialization-policy-whitelist GWT is adding undesired types to the serialization policy and bloating my JS. How do I trim my GWT whitelist by hand? Or should I at all? For example, if I put the interface List on a GWT RPC service class, GWT has to generate Javascript that handles ArrayList, LinkedList, Stack, Vector, ... even though my team knows we're only ever going to return an ArrayList. I could just make the method's return type ArrayList, but I like relying on an interface rather than a specific implementation. After all, maybe one day we will switch it up and return e.g. a LinkedList. In that case, I'd like to force the GWT serialization policy to compile for only ArrayList and LinkedList. No Stacks or Vectors. These implicit restrictions have one huge downside I can think of: a new member of the team starts returning Vectors, which will be a runtime error. So besides the question in the title, what is your experience designing around this?

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• Scrum stories and behind the scenes features

  - by James P.

  As I understand things, the Scrum backlog is composed of a series of Stories that represent something for the end user and this is further decomposed into Features. If this is the case, where does all the behind the scenes features go that aren't really linked to a story but are still useful? For example, say I'm making an application that catalogs the contents of a hard drive. A story wouldn't require it but having an md5 hash on each file would be a nice feature.

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• Why should I override hashCode() when I override equals() method?

  - by Bragaadeesh

  Ok, I have heard from many places and sources that whenever I override the equals() method, I need to override the hashCode() method as well. But consider the following piece of code package test; public class MyCustomObject { int intVal1; int intVal2; public MyCustomObject(int val1, int val2){ intVal1 = val1; intVal2 = val2; } public boolean equals(Object obj){ return (((MyCustomObject)obj).intVal1 == this.intVal1) && (((MyCustomObject)obj).intVal2 == this.intVal2); } public static void main(String a[]){ MyCustomObject m1 = new MyCustomObject(3,5); MyCustomObject m2 = new MyCustomObject(3,5); MyCustomObject m3 = new MyCustomObject(4,5); System.out.println(m1.equals(m2)); System.out.println(m1.equals(m3)); } } Here the output is true, false exactly the way I want it to be and I dont care of overriding the hashCode() method at all. This means that hashCode() overriding is an option rather being a mandatory one as everyone says. I want a second confirmation.

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• Enums and Annotations

  - by PeterMmm

  I want to use an Annotation in compile-safe form. To pass the value() to the Annotation i want to use the String representation of an enum. Is there a way to use @A with a value from enum E ? public class T { public enum E { a,b; } // C1: i want this, but it won't compile @A(E.a) void bar() { // C2: no chance, it won't compile @A(E.a.toString()) void bar2() { } // C3: this is ok @A("a"+"b") void bar3() { } // C4: is constant like C3, is'nt it ? @A(""+E.a) void bar4() { } } @interface A { String value(); }

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• Type-safe mapping from Class<T> to Thing<T>

  - by Joonas Pulakka

  I want to make a map-kind of container that has the following interface: public <T> Thing<T> get(Class<T> clazz); public <T> void put(Class<T> clazz, Thing<T> thing); The interesting point is that the Ts in each Class<T><- Thing<T> pair is the same T, but the container should be able to hold many different types of pairs. Initially I tried a (Hash)Map. But, for instance, Map<Class<T>, Thing<T>> is not right, because then T would be same T for all pairs in that map. Of course, Map<Class<?>, Thing<?>> works, but then I don't have type-safety guarantees so that when I get(String.class), I can't be sure that I get a Thing<String> instance back. Is there a way to accomplish the kind of type safety that I'm looking for?

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• Is System.nanoTime() consistent across threads?

  - by obvio171

  I want to count the time elapsed between two events in nanoseconds. To do that, I can use System.nanoTime() as mentioned here. The problem is that the two events are happening in different threads. Since nanoTime() doesn't return an absolute timestamp but instead can only be used to calculate time differences, I'd like to know if the values I get on the two different threads are consistent with the physical time elapsed between the two events.

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• Drawing graphics on top of a JButton

  - by trinth

  I have a situation wherein I have a bunch of JButtons on a GridLayout. I need each of the JButtons to have: a background image (but retain the ability to keep the default button look if needed) custom graphics drawn on top by other classes I have no trouble with the background image, since I am using setIcon() but I am having problems drawing things on top of the background. At one point I was able to draw on top of the button, but after the button was clicked, the drawings disappeared. How can make the button keep this drawing state? Basically, I need a way for my JButtons to have public methods that would allow another class to draw anything on it such as: public void drawSomething() { Graphics g = this.getGraphics(); g.drawOval(3,2,2,2); repaint(); } or public Graphics getGraphics() { return this.getGraphics(); } then another class could do this: button.getGraphics().drawSomething(); The latter is more what I am looking for but the first is equally useful. Is there any way to go about this? Also, overriding the parent class method paintComponent() doesn't help since I need each button to have different graphics.

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• if-else structure

  - by Halo

  I have these long statements that I will refer to as x,y etc. here. My conditional statements' structure goes like this: if(x || y || z || q){ if(x) do someth else if (y) do something if(z) do something else if(q) do something } else do smthing Is there a better, shorter way to write this thing? Thanks

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