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  • Java: Make a method abstract for each extending class

    - by Martijn Courteaux
    Hi, Is there any keyword or design pattern for doing this? public abstract class Root { public abstract void foo(); } public abstract class SubClass extends Root { public void foo() { // Do something } } public class SubberClass extends SubClass { // Here is it not necessary to override foo() // So is there a way to make this necessary? // A way to obligate the developer make again the override } Thanks

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  • How do Java mocking frameworks work?

    - by Amir Rachum
    This is NOT a question about which is the best framework, etc. I have never used a mocking framework and I'm a bit puzzled by the idea. How does it know how to create the mock object? Is it done in runtime or generates a file? How do you know its behavior? And most importantly - what is the work flow of using such a framework (what is the step-by-step for creating a test). Can anyone explain? You can choose whichever framework you like for example, just say what it is.

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  • java.math.BigInteger pow(exponent) question

    - by Jan Kraus
    Hi, I did some tests on pow(exponent) method. Unfortunately, my math skills are not strong enough to handle the following problem. I'm using this code: BigInteger.valueOf(2).pow(var); Results: var | time in ms 2000000 | 11450 2500000 | 12471 3000000 | 22379 3500000 | 32147 4000000 | 46270 4500000 | 31459 5000000 | 49922 See? 2,500,000 exponent is calculated almost as fast as 2,000,000. 4,500,000 is calculated much faster then 4,000,000. Why is that? To give you some help, here's the original implementation of BigInteger.pow(exponent): public BigInteger pow(int exponent) { if (exponent < 0) throw new ArithmeticException("Negative exponent"); if (signum==0) return (exponent==0 ? ONE : this); // Perform exponentiation using repeated squaring trick int newSign = (signum<0 && (exponent&1)==1 ? -1 : 1); int[] baseToPow2 = this.mag; int[] result = {1}; while (exponent != 0) { if ((exponent & 1)==1) { result = multiplyToLen(result, result.length, baseToPow2, baseToPow2.length, null); result = trustedStripLeadingZeroInts(result); } if ((exponent >>>= 1) != 0) { baseToPow2 = squareToLen(baseToPow2, baseToPow2.length, null); baseToPow2 = trustedStripLeadingZeroInts(baseToPow2); } } return new BigInteger(result, newSign); }

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  • Java Matcher groups: Understanding The difference between "(?:X|Y)" and "(?:X)|(?:Y)"

    - by user358795
    Can anyone explain: Why the two patterns used below give different results? (answered below) Why the 2nd example gives a group count of 1 but says the start and end of group 1 is -1? public void testGroups() throws Exception { String TEST_STRING = "After Yes is group 1 End"; { Pattern p; Matcher m; String pattern="(?:Yes|No)(.*)End"; p=Pattern.compile(pattern); m=p.matcher(TEST_STRING); boolean f=m.find(); int count=m.groupCount(); int start=m.start(1); int end=m.end(1); System.out.println("Pattern=" + pattern + "\t Found=" + f + " Group count=" + count + " Start of group 1=" + start + " End of group 1=" + end ); } { Pattern p; Matcher m; String pattern="(?:Yes)|(?:No)(.*)End"; p=Pattern.compile(pattern); m=p.matcher(TEST_STRING); boolean f=m.find(); int count=m.groupCount(); int start=m.start(1); int end=m.end(1); System.out.println("Pattern=" + pattern + "\t Found=" + f + " Group count=" + count + " Start of group 1=" + start + " End of group 1=" + end ); } } Which gives the following output: Pattern=(?:Yes|No)(.*)End Found=true Group count=1 Start of group 1=9 End of group 1=21 Pattern=(?:Yes)|(?:No)(.*)End Found=true Group count=1 Start of group 1=-1 End of group 1=-1

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  • Java Simple ActionListener Questions

    - by Allen
    I have a main class in a program that launches another class that handles all the GUI stuff. In the GUI, i have a button that i need to attach an ActionListener to. The only problem is, the code to be executed needs to reside within the main class. How can i get the ActionPerformed() method to execute in the main class when a button is clicked elsewhere?

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  • java: speed up reading foreign characters

    - by Yang
    My current code needs to read foreign characters from the web, currently my solution works but it is very slow, since it read char by char using InputStreamReader. Is there anyway to speed it up and also get the job done? // Pull content stream from response HttpEntity entity = response.getEntity(); InputStream inputStream = entity.getContent(); StringBuilder contents = new StringBuilder(); int ch; InputStreamReader isr = new InputStreamReader(inputStream, "gb2312"); // FileInputStream file = new InputStream(is); while( (ch = isr.read()) != -1) contents.append((char)ch); String encode = isr.getEncoding(); return contents.toString();

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  • Remove a child of root of XML using java

    - by Sachin Mhetre
    This is my xml file. - <deviceparameters> - <parameter componenttype="TextBox"> <name>Operating Type</name> <oid>1.3.6.1.4.1.31163.5.1.1</oid> <writable>true</writable> <description>The operating type defines which waveform type is used. This configuration takes several seconds to execute</description> - <paramvalues type="Integer"> <value default="No">123</value> </paramvalues> </parameter> - <parameter componenttype="TextBox"> <name>Active Waveform Status</name> <oid>1.3.6.1.4.1.31163.5.1.2</oid> <writable>false</writable> <description>Show the status of the waveform configured by operatingType</description> - <paramvalues type="String"> <value default="yes">Active</value> </paramvalues> </parameter> </deviceparameters> I want to remove node with name 'Active wavwform Status'. How can I reomve that particular node from xml. The code I have written is below. rootElement = doc.getDocumentElement(); NodeList nList = doc.getElementsByTagName("parameter"); String nodeName = TF_name.getText(); System.out.println(""+nList.getLength()); for (int temp = 0; temp < nList.getLength();temp++) { Node nNode = nList.item(temp); Element eElement = (Element) nNode; String upname1 = getTagValue("name", eElement); if(upname1.equals(nodeName)) { System.out.println("Parent: "+nNode.getParentNode().getNodeName()); System.out.println("nodename: "+nNode.getNodeName()); System.out.println("rmoving ...."); rootElement.removeChild(nNode); System.out.println("removed..."); } }

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  • Trying to convert a 2D image into 3D objects in Java

    - by Kyle
    Hey, I'm trying to take a simple image, something like a black background with colored blocks representing walls. I'm trying to figure out how to go about starting on something like this. Do I need to parse the image and look at each pixel or is there an easier way to do it? I'm using Java3D but it doesn't seem to have any sort of built in support for that...

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  • java shift elements in array

    - by Lightk3ira
    Hey I am trying to shift elements forward sending the last element in the array to data[0]. I did the opposite direction but I can't seem to find my mistake in going in this direction. Pos is users inputed shift times amount temp is the temporary holder. data is the array if(pos 0) { do { temp = data[data.length -1]; for(int i =0; i < data.length; i++) { if(i == data.length-1) { data[0] = temp; } else { data[i+1] = data[i]; } } pos--; }while(pos > 0); } Thanks.

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  • Java Stopping JApplet Components from Resizing based on Applet Size

    - by Doug
    Creating a JApplet I have 2 Text Fields, a button and a Text Area. private JPanel addressEntryPanel = new JPanel(new GridLayout(1,3)); private JPanel outputPanel = new JPanel(new GridLayout(1,1)); private JTextField serverTf = new JTextField(""); private JTextField pageTf = new JTextField(""); private JTextArea outputTa = new JTextArea(); private JButton connectBt = new JButton("Connect"); private JScrollPane outputSp = new JScrollPane(outputTa); public void init() { setSize(500,500); setLayout(new GridLayout(3,1)); add(addressEntryPanel); addressEntryPanel.add(serverTf); addressEntryPanel.add(pageTf); addressEntryPanel.add(connectBt); addressEntryPanel.setPreferredSize(new Dimension(50,50)); addressEntryPanel.setMaximumSize(addressEntryPanel.getPreferredSize()); addressEntryPanel.setMinimumSize(addressEntryPanel.getPreferredSize()); add(outputPanel); outputPanel.add(outputSp); outputTa.setLineWrap(true); connectBt.addActionListener(this); The problem is when debugging and putting it in a page the components / panels resize depending on the applet size. I don't want this. I want the textfields to be a certain size, and the text area to be a certain size. I've put stuff in there to set the size of them but they aren't working. How do I go about actually setting a strict size for either the components or the JPanel.

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  • I have problem using vesijama (Very Simple Java Mail)

    - by Huuhaacece
    Hi, i already read this tutorial from here and i have download all required libraries (Log4j, JavaMail API ,Activation framework) . But when i trying running this program i got this error log4j:WARN No appenders could be found for logger (org.codemonkey.vesijama.Mailer). org.codemonkey.vesijama.MailException: Generic error: Exception reading response log4j:WARN Please initialize the log4j system properly. this is the source code i use import javax.mail.Message.RecipientType; import org.codemonkey.vesijama.Email; import org.codemonkey.vesijama.MailException; import org.codemonkey.vesijama.Mailer; public class testSend { final Email email = new Email(); public testSend{ try{ email.setFromAddress("test", "[email protected]"); email.setSubject("hey"); email.addRecipient("hai", "[email protected]", RecipientType.TO); email.setText("We should meet up!"); email.setTextHTML("<b>We should meet up!</b>"); new Mailer("smtp.gmail.com", 465, "[email protected]", "XXXXXX").sendMail(email); } catch(MailException me) { System.out.println(me); } } } i have also trying using port 587. but i got same error .< btw , it say can add attachments what should i write if i want to attach .xls ( microsoft excel 2003) ? Thx B4.

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  • java: retrieving the "canonical value" from a Set<T> where T has a custom equals()

    - by Jason S
    I have a class Foo which overrides equals() and hashCode() properly. I would like to also would like to use a HashSet<Foo> to keep track of "canonical values" e.g. I have a class that I would like to write like this, so that if I have two separate objects that are equivalent I can coalesce them into references to the same object: class Canonicalizer<T> { final private Set<T> values = new HashSet<T>(); public T findCanonicalValue(T value) { T canonical = this.values.get(value); if (canonical == null) { // not in the set, so put it there for the future this.values.add(value); return value; } else { return canonical; } } } except that Set doesn't have a "get" method that would return the actual value stored in the set, just the "contains" method that returns true or false. (I guess that it assumes that if you have an object that is equal to a separate object in the set, you don't need to retrieve the one in the set) Is there a convenient way to do this? The only other thing I can think of is to use a map and a list: class Canonicalizer<T> { // warning: neglects concurrency issues final private Map<T, Integer> valueIndex = new HashMap<T, Integer>(); final private List<T> values = new ArrayList<T>(); public T findCanonicalValue(T value) { Integer i = this.valueIndex.get(value); if (i == null) { // not in the set, so put it there for the future i = this.values.size(); this.values.add(value); this.valueIndex.put(value, i); return value; } else { // in the set return this.values.get(i); } } }

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  • quick java question

    - by j-unit-122
    private static char[] quicksort (char[] array , int left , int right) { if (left < right) { int p = partition(array , left, right); quicksort(array, left, p - 1 ); quicksort(array, p + 1 , right); } for (char i : array) System.out.print(i + ” ”); System.out.println(); return array; } private static int partition(char[] a, int left, int right) { char p = a[left]; int l = left + 1, r = right; while (l < r) { while (l < right && a[l] < p) l++; while (r > left && a[r] >= p) r--; if (l < r) { char temp = a[l]; a[l] = a[r]; a[r] = temp; } } a[left] = a[r]; a[r] = p; return r; } } hi guys just a quick question regarding the above coding, i know that the above coding returns the following B I G C O M P U T E R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M O P T U R B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U when the sequence BIGCOMPUTER is used but my question is can someone explain to me what is happening in the code and how? i know abit about the quick-sort algorithm but it doesnt seem to be the same in the above example.

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  • How would you code an efficient Circular Buffer in Java or C#

    - by Cheeso
    I want a simple class that implements a fixed-size circular buffer. It should be efficient, easy on the eyes, generically typed. EDIT: It need not be MT-capable, for now. I can always add a lock later, it won't be high-concurrency in any case. Methods should be: .Add and I guess .List, where I retrieve all the entries. On second thought, Retrieval I think should be done via an indexer. At any moment I will want to be able to retrieve any element in the buffer by index. But keep in mind that from one moment to the next Element[n] may be different, as the Circular buffer fills up and rolls over. This isn't a stack, it's a circular buffer. Regarding "overflow": I would expect internally there would be an array holding the items, and over time the head and tail of the buffer will rotate around that fixed array. But that should be invisible from the user. There should be no externally-detectable "overflow" event or behavior. This is not a school assignment - it is most commonly going to be used for a MRU cache or a fixed-size transaction or event log.

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  • Java heap size - will this work?

    - by UnCon
    Hi, I try this with NetBeans desktop application template - increasing heapsize (to 512 MiB) of executed .jar file. (I believe that NetBeans uses Singleton app by default - SingleFrameView) Will it work? public static void main(String[] args) { if (args == null) { args = new String[1]; args[0] = "Xmx512m"; } else { String[] tempArgs = new String[args.length+1]; for (int i=0; i<args.length; i++) { tempArgs[i] = args[i]; } tempArgs[tempArgs.length-1] = "Xmx512m"; args = tempArgs; } launch(MyApp.class, args); } }

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  • Incorrect Date in Java

    - by Polaris
    I use next code to print current time Calendar cal = Calendar.getInstance(); System.out.println(cal.getTime()); I have Windows XP sp3 istalled. Current time in system tray is 14:30. But this code return 13:30 Why returned time is wrong?

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  • HELP easy java program [closed]

    - by gentrit
    type first integer , type second integer, , program repeatedly outputs the second value of the number of times indicated by the first value. Example use inputs 4 and 2, 222 2 displayed. another example user inputs 3 and 8 , 88 8 displayed

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  • Java: using generic wildcards with subclassing

    - by gibberish
    Say I have a class Foo, a class A and some subclass B of A. Foo accepts A and its sublclasses as the generic type. A and B both require a Foo instance in their constructor. I want A's Foo to be of type A , and B's Foo to be of type B or a superclass of B. So in effect, So I only want this: Foo<X> bar = new Foo<X>; new B(bar); to be possible if X is either A, B, or a both subclass of A and superclass of B. So far this is what I have: class Foo<? extends A>{ //construct } class A(Foo<A> bar){ //construct } class B(Foo<? super B> bar){ super(bar); //construct } The call to super(...) doesn't work, because <A> is stricter than <? super B>. Is it somehow possible to use the constructor (or avoid code duplication by another means) while enforcing these types? Edit: Foo keeps a collection of elements of the generic parameter type, and these elements and Foo have a bidirectional link. It should therefore not be possible to link an A to a Foo.

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  • How to copy .java sources to Ant javac destFolder

    - by Ittai
    Hi, I know how to use Ant to copy files and folders but what I'm interested in is if, and how, I can have the javac task copy the same sources it's compiling to the output directory. Basically, it's very similar to the option to include your sources in the jar task. Thanks in advance, Ittai

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  • I have a problem with the following Java code

    - by Sanjeev
    public class b { public static void main(String[] args) { byte b = 1; long l = 127; // b = b + l; // 1 if I try this then it does not compile b += l; // 2 if I try this then it does compile System.out.println(b); } } I am using this code but I have problem: I don't understand why b=b+l; is not compiling but if I write b+=l; then it compiles and runs. Please explain why this happens.

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