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  • interface as a method parameter in Java

    - by PeterYu
    Hi all, I had an interview days ago and was thrown a question like this. Q: Reverse a linked list. Following code is given: public class ReverseList { interface NodeList { int getItem(); NodeList nextNode(); } void reverse(NodeList node) { } public static void main(String[] args) { } } I was confused because I did not know an interface object could be used as a method parameter. The interviewer explained a little bit but I am still not sure about this. Could somebody enlighten me?

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  • Java - JPA - @Version annotation

    - by Yatendra Goel
    I am new to JPA. I am cofused about the @Version annotation. How it works? I have googled it and found various answers whose extract is as follows: JPA uses a version field in your entities to detect concurrent modifications to the same datastore record. When the JPA runtime detects an attempt to concurrently modify the same record, it throws an exception to the transaction attempting to commit last. But still I am not sure how it works? ================================================================================== Also as from the following lines: You should consider version fields immutable. Changing the field value has undefined results. Does it mean that we should declare our version field as final

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  • Java String object creation

    - by Ajay
    Hi, 1) What is difference in thers two statements: String s1 = "abc"; and String s1 = new String("abc") 2) as i am not using new in first statement, how string object will be created Thanks

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  • java web templates across multiple WAR files

    - by Casey
    I have a multi WAR web application that was designed badly. There is a single WAR that is responsible for handling some authorization against a database and defines a standard web page using a jsp taglib. The main WAR basically checks the privileges of the user and than based on that, displays links to the context path of the other deployed WARS. Each of the other deployed WARs includes this custom tag lib. I am working on redesigning this application, and one of the nice things that I want to retain is that we have other project teams that have developed these WAR modules that "plug into" our current system to take advantage of other things we have to offer. I am not entirely sure how to handle the page templates though. I need a templating system that would be easy enough to use across multiple wars (I was thinking of jsp fragments??). I really only need to define a consistent header and main navigation section. Whatever else is displayed on the page is up to the individual web project. Any suggestions? I hope that this is clear, if not I can elaborate more.

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  • Returning string in java using 3 parameters

    - by user2905118
    Need to write a method describePerson() that takes 3 parameters, a String giving a person’s name, a boolean indicating their gender (true for female, false for male), and an integer giving their age. The method should return a String formatted as in the following examples: Lark is female. She is 2 years old. Or Jay is male. He is 1 year old. I am not sure how to write it correctly (my code): int describePerson(String name, boolean gender, int age) { String words=""; if(gender==true) return (name + "is "+gender+". "+"She is"+age+ "years old.); else return (name + "is "+gender+". "+"She is"+age+ "years old.); } The outcome "year" and "years" is also differs, but i don't know how to make it correct..

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  • Creating a New Reverse Java Array

    - by mandir08
    Given an array of ints length 3, return a new array with the elements in reverse order, so {1, 2, 3} becomes {3, 2, 1}. public int[] reverse3(int[] nums) { int[] values = new int[3]; for(int i=0; i<=nums.length-1; i++) { for(int j=nums.length-1; j>=0; j--) { values[i]=nums[j]; } } return values; } I cant get this to work properly, usually the last int in the array, becomes every single int in the new array

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  • java overloaded method

    - by Sean Nguyen
    Hi, I have an abstract template method: class abstract MyTemplate { public void something(Object obj) { doSomething(obj) } protected void doSomething(Object obj); } class MyImpl extends MyTemplate { protected void doSomething(Object obj) { System.out.println("i am dealing with generic object"); } protected void doSomething(String str) { System.out.println("I am dealing with string"); } } public static void main(String[] args) { MyImpl impl = new MyImpl(); impl.something("abc"); // --> this return "i am dealing with generic object" } How can I print "I am dealing with string" w/o using instanceof in doSomething(Object obj)? Thanks,

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  • Java Split not working as expected

    - by daaabears
    I am trying to use a simple split to break up the following string: 00-00000 My expression is: ^([0-9][0-9])(-)([0-9])([0-9])([0-9])([0-9])([0-9]) And my usage is: String s = "00-00000"; String pattern = "^([0-9][0-9])(-)([0-9])([0-9])([0-9])([0-9])([0-9])"; String[] parts = s.split(pattern); If I play around with the Pattern and Matcher classes I can see that my pattern does match and the matcher tells me my groupCount is 7 which is correct. But when I try and split them I have no luck.

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  • What is the use of reflection in Java/C# etc

    - by zengr
    I was just curious, why should we use reflection in the first place? // Without reflection Foo foo = new Foo(); foo.hello(); // With reflection Class cls = Class.forName("Foo"); Object foo = cls.newInstance(); Method method = cls.getMethod("hello", null); method.invoke(foo, null); We can simply create an object and call the class's method, but why do the same using forName, newInstance and getMthod functions? To make everything dynamic?

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  • Maven easyb plugin java heap space settings?

    - by vinnu
    Hi, I attempted to change my heap size for maven easyb plugin http://www.easyb.org/maven-easyb-plugin/. In my easyb test I added standard code to print the heap size using the code Runtime.getFreeMemory() and Runtime.getTotalMemory(). I tried setting the MAVEN_OPTS=-Xmx1024m -Xms1024m and also set the maven opts in Maven surefire plugin. Now when I run the same class from the Junit I can see the getTotalMemory() displaying a number close 1Gig but the when the same classes are invoked from easyb plugin they do not reflect the memory size. Shouldn't there be a way of passing JVM opts to maven easyb plugin when it runs these easyb tests? At the very minimum it should atleast pick up the MAVEN_OPTS settings from the environment. Has someone bumped into problems like this? (A search on this group's archive does not reveal much)

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  • StringBufferInputStream Question in Java

    - by JJG
    I want to read an input string and return it as a UTF8 encoded string. SO I found an example on the Oracle/Sun website that used FileInputStream. I didn't want to read a file, but a string, so I changed it to StringBufferInputStream and used the code below. The method parameter jtext, is some Japanese text. Actually this method works great. The question is about the deprecated code. I had to put @SuppressWarnings because StringBufferInputStream is deprecated. I want to know is there a better way to get a string input stream? Is it ok just to leave it as is? I've spent so long trying to fix this problem that I don't want to change anything now I seem to have cracked it. @SuppressWarnings("deprecation") private String readInput(String jtext) { StringBuffer buffer = new StringBuffer(); try { StringBufferInputStream sbis = new StringBufferInputStream (jtext); InputStreamReader isr = new InputStreamReader(sbis, "UTF8"); Reader in = new BufferedReader(isr); int ch; while ((ch = in.read()) > -1) { buffer.append((char)ch); } in.close(); return buffer.toString(); } catch (IOException e) { e.printStackTrace(); return null; } }

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  • Java - 'continue' loop iteration after certain timeout period

    - by Matt
    Is there a way to exit ('continue;') a loop iteration after a certain timeout period? I have a loop that will run gathering data from the web and then use this data to make a calculation. The data become obsolete after about 1 to 2 seconds so if the loop iteration takes longer than 1 second then i want it to 'continue' to the next iteration. Sometimes gathering the data can take time but sometimes the calculation can take longer than 1 second so a HTTP timeout won't work for what i need. Also, while doing the calculation the thread i am using is blocked so i cannot check System.currentTimeMillis(); Is there a way to use another Thread to check the time and force the original for loop to continue.

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  • java hashmap array to double array

    - by Tweety
    Hi, I declared LinkedHashMap<String, float[]> and now I want to convert float[] values into double[][]. I am using following code. LinkedHashMap<String, float[]> fData; double data[][] = null; Iterator<String> iter = fData.keySet().iterator(); int i = 0; while (iter.hasNext()) { faName = iter.next(); tValue = fData.get(faName); //data = new double[fData.size()][tValue.length]; for (int j = 0; j < tValue.length; j++) { data[i][j] = tValue[j]; } i++; } When I try to print data System.out.println(Arrays.deepToString(data)); it doesn't show the data :( I tried to debug my code and i figured out that I have to initialize data outside the while loop but then I don't know the array dimensions :( How to solve it? Thanks

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  • How do I alias the scala setter method 'myvar_$eq(myval)' to something more pleasing when in java?

    - by feydr
    I've been converting some code from java to scala lately trying to teach myself the language. Suppose we have this scala class: class Person() { var name:String = "joebob" } Now I want to access it from java so I can't use dot-notation like I would if I was in scala. So I can get my var's contents by issuing: person = Person.new(); System.out.println(person.name()); and set it via: person = Person.new(); person.name_$eq("sallysue"); System.out.println(person.name()); This holds true cause our Person Class looks like this in javap: Compiled from "Person.scala" public class Person extends java.lang.Object implements scala.ScalaObject{ public Person(); public void name_$eq(java.lang.String); public java.lang.String name(); public int $tag() throws java.rmi.RemoteException; } Yes, I could write my own getters/setters but I hate filling classes up with that and it doesn't make a ton of sense considering I already have them -- I just want to alias the _$eq method better. (This actually gets worse when you are dealing with stuff like antlr because then you have to escape it and it ends up looking like person.name_\$eq("newname"); Note: I'd much rather have to put up with this rather than fill my classes with more setter methods. So what would you do in this situation?

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  • Java File manipulation

    - by user69514
    So I have an application with a JFileChooser from which I select a file to read. Then I change some words and write a new file. The problem that I am having is that when I write the new file it's saved in the project directory. How do I save it in the same directory as the file that I chose using the JFileChooser. Note: I don't want to use the JFileChooser to choose the location. I just need to save the file in the same directory as the original file that I read.

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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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  • Java Object Creation Error

    - by ikurtz
    package Sartre.Connect4; import javax.swing.*; public class ChatGUI extends JDialog { public ChatGUI(){ setTitle("Chat"); } } when i do this in another class in the same package: ChatGUI chatGUI = new ChatGUI(); i end up with a situation: Cannot Find Symbol please help?

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  • Java Detect Variable Change Using PropertyChangeSupport and PropertyChangeListener

    - by Sam
    I'm trying to print out debug statements when some third party code changes a variable. For example, consider the following: public final class MysteryClass { private int secretCounter; public synchronized int getCounter() { return secretCounter; } public synchronized void incrementCounter() { secretCounter++; } } public class MyClass { public static void main(String[] args) { MysteryClass mysteryClass = new MysteryClass(); // add code here to detect calls to incrementCounter and print a debug message } I don't have the ability to change the 3rd party MysteryClass, so I thought that I could use PropertyChangeSupport and PropertyChangeListener to detect changes to the secretCounter: public class MyClass implements PropertyChangeListener { private PropertyChangeSupport propertySupport = new PropertyChangeSupport(this); public MyClass() { propertySupport.addPropertyChangeListener(this); } public void propertyChange(PropertyChangeEvent evt) { System.out.println("property changing: " + evt.getPropertyName()); } public static void main(String[] args) { MysteryClass mysteryClass = new MysteryClass(); // do logic which involves increment and getting the value of MysteryClass } } Unfortunately, this did not work and I have no debug messages printed out. Does anyone see what is wrong with my implementation of the PropertyChangeSupport and Listener interfaces? I want to print a debug statement whenever incrementCounter is called or the value of secretCounter changes.

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  • Output Parameter in java

    - by soclose
    Hi, could u give me a sample code of using output parameter in function? I tried to google it but just found it in function. I'd like to use this output value in another function. I will use this code in Android.

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  • Java - Syntax Question: What is <? super T>

    - by aloh
    I'm having trouble understanding the following syntax: public class SortedList< T extends Comparable< ? super T> > extends LinkedList< T > I see that class SortedList extends LinkedList. I just don't know what T extends Comparable< ? super T> means. My understanding of it so far is that type T must be a type that implements Comparable...but what is "< ? super T "?

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  • Java Applet - ArrayIndexOutOfBoundsException

    - by Dan
    OK so I am getting an ArrayIndexOutofBoundsException. I don't know why. Here's my code: http://www.so.pastebin.com/y5MjD1k3 The thing is when I go to the red brick at board[2][2]... I go there. Then I go up... then I TRY go to back down but that error pops up. Also when I go to the right 8 squares... I ALSO get that error. ALSO, pretend my 2d map is split into FOUR squares... well square one is the top left... if I go ANYWHERE else ... I get that error. What am I doing wrong? Thanks.

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  • Implementing Clonable in Java

    - by Artium
    In which cases should I use this way: public A clone() throws CloneNotSupportedException { A clone = (A)super.clone(); clone.x= this.x; return clone; } And in which cases should I use that way: public ShiftedStack clone() throws CloneNotSupportedException { return new A(this.x); } What should I do if x is final and I want to use the first way? Regarding the first way, I understand it like this: we clone the super class and up-cast it, leading to some members uninitialized. After this initialize these members. Is my understanding correct? Thank you.

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