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  • Java - problems with polymorphism

    - by cc0
    I have a book class, then a novel- and a science book class that extend the book class. I made an ArrayList using the book class, then inserted the novels and the science books into that. Now I'm trying to iterate through the ArrayList to count how many novels are there. How can I tell? Would love to see some examples of this! I've been at it for a while.

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  • Proper usage of Java Weak Reference in case of nested collections

    - by Tong Wang
    I need to define a weak reference Map, whose value is a Set. I use Google collections' MapMaker, like this: Map<Class<? extends Object>, Set<Foo>> map = new MapMaker().weakKeys().weakValues().makeMap(); So, for Set<Foo>, can I use a normal HashSet? Or, do I have to create a weak HashSet, like this: Collections.newSetFromMap(new WeakHashMap<Foo, Boolean>()); And why? Another question, the key of my map is Class objects, when will a Class object become weakly reachable? In other words, what is the lifetime of a Class object? Thanks.

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  • Get n Number of words using regex in Java

    - by Aymon Fournier
    I have a section of a book, complete with punctuation, line breaks etc. and I want to be able to extract the first n words from the text, and divide that into 5 parts. Regex mystifies me. This is what I am trying. I creates an array of index size 0, with all the input text: public static String getNumberWords2(String s, int nWords){ String[] m = s.split("([a-zA-Z_0-9]+\b.*?)", (nWords / 5)); return "Part One: \n" + m[1] + "\n\n" + "Part Two: \n" + m[2] + "\n\n" + "Part Three: \n" + m[3] + "\n\n" + "Part Four: \n" + m[4] + "\n\n" + "Part Five: \n" + m[5]; } Thanks!

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  • ConcurentModificationException in Java HashMap

    - by Bear
    Suppose I have two methods in my classes, writeToMap() and processKey() and both methods are called by multiple threads. writeToMap is a method to write something in hashmap and processKey() is used to do sth based on the keySet of HashMap. Inside processKey, I first copy the originalMap before getting the key set. new HashMap<String, Map<String,String>(originalMap).get("xx").keySet(); But I am still getting ConcurrentModificationException even though I always copy the hashmap. Whats the problem?

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  • Question About Eclipse Java Debugger Conditional Breakpoints Inefficiency

    - by Personman
    I just set a conditional breakpoint in Eclipse's debugger with a mildly inefficient condition by breakpoint standards - checking whether a HashMap's value list (8 elements) contains Double.NaN. This resulted in an extremely noticeable slowdown in performance - after about five minutes, I gave up. Then I copy pasted the condition into an if statement at the exact same line, put a noop in the if, and set a normal breakpoint there. That breakpoint was reached in the expected 20-30 seconds. Is there something special that conditional breakpoints do that is different from this, or is Eclipse's implementation just kinda stupid? It seems like they could fairly easily just do exactly the same thing behind the scenes.

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  • What's a good FOSS java servlet session replication solution

    - by Bossy Joe
    I work on a very high volume public website running on Tomcat 5.5. Currently we require stickiness to a particular server in order to maintain session. I'd like to start replicating session, but have had trouble finding a good FOSS solution. I've written my own Manager (using memcached as the store) but am having trouble dealing with race conditions if more than one server is handling the requests for the same user. Is there a solution out there I should be looking at? I'm looking for not just something that works as a fallback if stickiness fails, but that would work if user requests are regularly spread to multiple servers.

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  • Java regular expression: how to include '-'

    - by changed
    I am using this pattern and matching a string. String s = "//name:value /name:value"; if (s.matches("(//?\\s*\\w+:\\w+\\s*)+")) { // it fits } This works properly. But if I want to have a string like "/name-or-address:value/name-or-address:value" which has this '-' in second part, it doesn't work. I am using \w to match A-Za-z_, but how can I include - in that?

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  • Collision detection in Java game?

    - by Chetan
    I am developing a game in which I have the problem of collision detection of moving images. The game has a spaceship and number of asteroids (obstacles). I want to detect the collision between them. How can I do this?

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  • Java: Protected classes?

    - by incrediman
    I'd like to be able to have two protected classes in my package. That is, I do not want files outside of my package to see them as visible - they will be for internal use within the package only. How can I do this?

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  • -Java- Swing GUI - Moving around components specifically with layouts

    - by Xemiru Scarlet Sanzenin
    I'm making a little test GUI for something I'm making. However, problems occur with the positioning of the panels. public winInit() { super("Chatterbox - Login"); try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch(ClassNotFoundException e) { } catch (InstantiationException e) { } catch (IllegalAccessException e) { } catch (UnsupportedLookAndFeelException e) { } setSize(300,135); pn1 = new JPanel(); pn2 = new JPanel(); pn3 = new JPanel(); l1 = new JLabel("Username"); l2 = new JLabel("Password"); l3 = new JLabel("Random text here"); l4 = new JLabel("Server Address"); l5 = new JLabel("No address set."); i1 = new JTextField(10); p1 = new JPasswordField(10); b1 = new JButton("Connect"); b2 = new JButton("Register"); b3 = new JButton("Set IP"); l4.setBounds(10, 12, getDim(l4).width, getDim(l4).height); l1.setBounds(10, 35, getDim(l1).width, getDim(l1).height); l2.setBounds(10, 60, getDim(l2).width, getDim(l2).height); l3.setBounds(10, 85, getDim(l3).width, getDim(l3).height); l5.setBounds(l4.getBounds().width + 14, 12, l5.getPreferredSize().width, l5.getPreferredSize().height); l5.setForeground(Color.gray); i1.setBounds(getDim(l1).width + 15, 35, getDim(i1).width, getDim(i1).height); p1.setBounds(getDim(l1).width + 15, 60, getDim(p1).width, getDim(p1).height); b1.setBounds(getDim(l1).width + getDim(i1).width + 23, 34, getDim(b2).width, getDim(b1).height - 5); b2.setBounds(getDim(l1).width + getDim(i1).width + 23, 60, getDim(b2).width, getDim(b2).height - 5); b3.setBounds(getDim(l1).width + getDim(i1).width + 23, 10, etDim(b2).width, getDim(b3).height - 5); b1.addActionListener(clickButton); b2.addActionListener(clickButton); b3.addActionListener(clickButton); pn1.setLayout(new FlowLayout(FlowLayout.RIGHT)); pn2.setLayout(new FlowLayout(FlowLayout.RIGHT)); pn1.add(l1); pn1.add(i1); pn1.add(b1); pn2.add(l2); pn2.add(p1); pn2.add(b2); add(pn1); add(pn2); } I am attempting to use FlowLayout to position the panels in the way desired. I'd use BorderLayout while adding, but the vertical spacing is too far away when I just use directions closest to one another. The output of this code is to create a window, 300,150, place whatever's in the two panels in the exact same spaces. Yes, I realize there's useless code there with setBounds(), but that was just me screwing around with Absolute Positioning, which wasn't working out for me either.

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  • Deferred printing in Java

    - by Bober02
    I have a specific issue with general console printing and I was wondering whether anyone has a solution for it. I am trying to print a dataTable which would look like sth like this: Table ---------------------- Name |Surname | ---------------------- Mike |Mikhailowish| Rafaello|Mirena | and so on. In order to print the border of the bar I need to know what the maximum length of each column value is. I don't want to go through the whole database to find that out and then again to print it. I would rather like to do sth like: System.out.printLater(s); //herejust leave a pointer to a StringBuilder you will build ... s.append("--------"); ... System.out.printAllDeferred(); I understand the above is probably in 99.99999% chances impossible, but perhaps you guys have a clever way of achieving the above?

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  • Regex to match a Java method signature

    - by nitesh
    I am having this particular requirement where a method has to be identified by different regular expressions for different components. For example, there need to be a regex for return parameter, one for method name, one for argument type and one for argument name. I was able to come up with an expression till this step as follows - ([^,]+) ([^,]+)\((([^,]+) ([^,]+))\) It works well for a method signature like - ReturnType foo(Arg parameter) The regular expression identifies ReturnType, foo, Arg and parameter separately. Now the problem is that a method can have no/one/multiple arguments separated by commas. I am not able to get a repeating expression for this. Help will be appreciated.

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  • How to append to an array that contains blank spaces - Java

    - by Cameron Townley
    I'm trying to append to a char[] array that contains blank spaces on the end. The char array for example contains the characters 'aaa'. When I append the first time the method functions properly and outputs 'aaabbb'. The initial capacity of the array is set to 80 or multiples of 80. The second time I try and append my output looks like"aaabbb bbb". Any psuedocode would be great.

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  • Java > SimpleDateFormat > Month + 1 Why ?

    - by Natim
    Hello, I am using SimpleDateFormat to display a Calendar like this : public String getDate() { String DATE_FORMAT = "EEEE, dd/MM/yyyy HH:mm:ss"; SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT); System.err.println(date.getTime().getMonth()); return sdf.format(date.getTime()); } The shell returns 6 and the display : mardi, 06/07/2010 12:44:52 It can't be possible ? Why ? Thanks

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  • How does ambigous methods are resolved in java ?

    - by Jijoy
    Hi , I do have a question. package org.study.algos; public class Study { public static void main(String[] args) { A a = new A(); a.m1(null); } } class A { public void m1(String s) { System.out.println("String"); System.out.println(s); } public void m1(Object obj) { System.out.println("Object"); System.out.println(obj); } } Here , the output is String null Why JVM resolve the method to one with String arguement ? Thanks in advance J

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  • Regular expressions in java

    - by rookie
    String s= "(See <a href=\"/wiki/Grass_fed_beef\" title=\"Grass fed beef\" " + "class=\"mw-redirect\">grass fed beef.) They have been used for " + "<a href=\"/wiki/Paper\" title=\"Paper\">paper-making since " + "2400 BC or before."; In the string above I have inter-mixed html with text. Well the requirement is that the output looks like:- They have been used for paper-making since 2400 BC or before. Could some one help me with a generic regular expression that would produce the desired output from the given input? Thanks in advance!

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  • Java replace all capturing groups

    - by Don
    Hi, If I have a regex with a capturing group, e.g. foo(g.*f). If I match this against a string and want to replace the first capturing group in all matches with baz so that foog___f blah foog________f is converted to: foobaz blah foobaz There doesn't appear to be any easy way to do this using the standard libraries, because the Matcher.replaceAll() method will only replace all matches of the entire pattern, am I missing something? Obviously I can just iterate through the matches, store the start and end index of each capturing group, then go back and replace them, but is there an easier way? Thanks, Don

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  • Dynamically assembling SQL queries in Java

    - by kd
    What is the best way to assemble an SQL query with join conditions dynamically? I don't want to hard code the query for each different condition on a webpage or a set of webpages. Is it even feasible? I got as far as being able to assemble simple queries but i got stumped when i needed to insert join conditions, i.e. how to figure out dependencies for joins etc.

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  • java table question

    - by kate
    hello i have a issue and i want your help i have a table which is called citylink[10][2] and i want to make a check before i move on in my code if it's full to continue if it's not to break!!i know that i should use an if loop but i don't know what to put inside it!!

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