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  • Hash Tables - Java

    - by Antony
    Am about to do a homework, and i need to store quite a lot of information (Dictionary) in a data structure of my choice. I heard people in my classroom saying hash-tables are the way to go. How come?

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  • best way to create UI java apps ?

    - by fwfwfw
    I've come across Netbeans but is there any tools out there that lets you build things event driven ? I'm looking for a feature like being able to drag and drop UI components, and add methods to buttons directly by double clicking it (kinda like visualbasic) and viewing the source.

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  • Strange behavior when overloading methods in Java

    - by Sep
    I came across this weird (in my opinion) behavior today. Take this simple Test class: public class Test { public static void main(String[] args) { Test t = new Test(); t.run(); } private void run() { List<Object> list = new ArrayList<Object>(); list.add(new Object()); list.add(new Object()); method(list); } public void method(Object o) { System.out.println("Object"); } public void method(List<Object> o) { System.out.println("List of Objects"); } } It behaves the way you expect, printing "List of Objects". But if you change the following three lines: List<String> list = new ArrayList<String>(); list.add(""); list.add(""); you will get "Object" instead. I tried this a few other ways and got the same result. Is this a bug or is it a normal behavior? And if it is normal, can someone explain why? Thanks.

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  • Waiting for a subset of threads in a Java ThreadPool

    - by David Semeria
    Let's say I have a thread pool containing X items, and a given task employs Y of these items (where Y is much smaller than X). I want to wait for all of the threads of a given task (Y items) to finish, not the entire thread pool. If the thread pool's execute() method returned a reference to the employed thread I could simply join() to each of these Y threads, but it doesn't. Does anyone know of an elegant way to accomplish this? Thanks.

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  • Java LinkedList iterator being exhausted prematurely

    - by Sujeet
    I am using LinkedList and retrieving an Iterator object by using list.iterator(). After that, I am checking it.hasNext(), real issue is while checking it.hasNext(), sometimes it returns false. I need help why this is happening, though I have elements in the list. Some code: public synchronized void check(Object obj) throws Exception { Iterator itr = list.iterator(); while(itr.hasNext()) { //This Line I get false.. though i have list size is 1 Item p = (Item)itr.next(); if(p.getId() == null) {continue;} if(p.getId().getElemntId() == obj.getId() || obj.getId() == 0 ) { p.setResponse(obj); notifyAll(); return; } } Log.Error("validate failed obj.getId="+obj.getId()+" **list.size="+list.size()*This shows 1*); throw new Exception("InvalidData"); }

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  • How to build our own java custom layout

    - by nguyendat
    Please help me how to creat own custom layout, container, component, layout manager... Example: Containers and Layout Managers Create a window frame. Nest panels within a frame for better layout control. Create and display buttons in a panel. List two component attributes that are controlled by a layout manager. Set the layout manager for a container. Place components in a panel using BorderLayout, GridLayout, and FlowLayout. Name one advantage of each of the layout managers. Create panels with titles. i was search on google but can't find any that match my requirement Thanks for your help

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  • Java : Count even values in a Binary Search Tree recursively

    - by user307682
    Hi, I need to find out how many even values are contained in a binary tree. this is my code. private int countEven(BSTNode root){ if ((root == null)|| (root.value%2==1)) return 0; return 1+ countEven(root.left) + countEven(root.right); } this i just coded as i do not have a way to test this out. I'm not able to test it out at the moment but need an answer so badly. any help is deeply appreciated.

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  • ArithmeticException Java?

    - by KP65
    Can anyone help me find where the execption is? I can't seem to find the problem.. public void fieldChanged(Field f, int context){ //if the submit button is clicked try{ stopTime = System.currentTimeMillis(); timeTaken = stopTime - startTime; timeInSecs = ((timeTaken/1000)); speed = 45/timeInSecs; Dialog.alert("Speed of Delivery: " + speed + "mph"); } catch(ArithmeticException e){ Dialog.alert("error " + speed); e.printStackTrace(); } } startTime variable is a global variable..

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  • Confusion in multi dimensional array in Java

    - by Alvin
    Hello, I'm not able to understand the following multi-dimensional code. Could someone please clarify me? int[][] myJaggedArr = new int [][] { new int[] {1,3,5,7,9}, new int[] {0,2,4,6}, new int[] {11,22} }; May I know how it is different from the following code? int[][] myArr = new int [][] { {1,3,5,7,9}, {0,2,4,6}, {11,22} };

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  • URL Routing in Java

    - by Jack
    Coming from other web frameworks, I'm used to being able to map parts of a URL to method parameters. I know that web.xml provides a way to map an entire URL to a Servlet but is there a way to get more features out of this, such as mapping pieces of the URL to method parameters?

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  • Regular expression one or more times JAVA

    - by user1381564
    Hi i am trying to match a string against a pattern this is the possible string signal CS, NS, dl: stateType := writeOrRead0; signal CS, pS : stateType := writeOrRead0; signal dS : stateType := writeOrRead0; i am only concerned with the pattern as far as the first colon. but the number of signals define can be more than one it could be three or four even this is the regular expression i have ^signal\\s*(\\w+),*\\s*(\\w+)\\s*: it will pick up the second two signal but and for the second one it picks up CS and pS and but the d and S in the next signal when i use matcher.group() come up seperately Can anyone give me an expression that will pick up all signal names whether there is one two three or more?

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  • Java : Using parent class method to access child class variable

    - by Jayant
    I have the following scenario : public class A { private int x = 5; public void print() { System.out.println(x); } } public class B extends A { private int x = 10; /*public void print() { System.out.println(x); }*/ public static void main(String[] args) { B b = new B(); b.print(); } } On executing the code, the output is : 5. How to access the child class(B's) variable(x) via the parent class method? Could this be done without overriding the print() method (i.e. uncommenting it in B)? [This is important because on overriding we will have to rewrite the whole code for the print() method again]

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  • Java code compression and decompression of a string

    - by user1822710
    I am having a problem figuring how to check a string for the same characters in a row then count that same character in a row then printing it out then giving the location of the last occorance of that character count then printing it out then moving to the next character in the string that is different then the previous character and the program is case sensitive. So the input could be: aaaaAAAbbbddccc How would I compress this string to: a4A3b3d2c3 ? and then decompress it?

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  • Android Java error handling XML file

    - by Paul
    I'm using SAX and XML reader to read XML weather info from the web and it works fine if the page exists. But if for instance the user inputs an invalid city, zip etc the XML page that gets read from is empty and the app force closes with nullpointerexception. The area that generates the error is here right at open inputstream. Any suggestions?: SAXParserFactory spf = SAXParserFactory.newInstance(); SAXParser sp = null; try { sp = spf.newSAXParser(); } catch (ParserConfigurationException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SAXException e) { // TODO Auto-generated catch block e.printStackTrace(); } /* Get the XMLReader of the SAXParser we created. */ XMLReader xr = null; try { xr = sp.getXMLReader(); } catch (SAXException e) { // TODO Auto-generated catch block e.printStackTrace(); } /* Create a new ContentHandler and apply it to the XML-Reader*/ WeatherHandler myExampleHandler = new WeatherHandler(); xr.setContentHandler(myExampleHandler); /* Parse the xml-data from our URL. */ try { xr.parse(new InputSource(url.openStream())); parsedWeatherDataSet = myExampleHandler.getParsedData(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SAXException e) { // TODO Auto-generated catch block e.printStackTrace(); } return parsedWeatherDataSet.toString();

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  • Rotation in a Vector2d class in Java

    - by wanstein
    I've been working on this for one hour, just can't get it. I have a Vector2d class: public class Vector2d { public double x = 0.0; public double y = 0.0; .... } This vector class has a rotate() method which is causing me trouble. The first snippet seems to make the x and y values smaller and smaller. The second one works just fine! Am I missing something simple here? public void rotate(double n) { this.x = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); this.y = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); } This works: public void rotate(double n) { rx = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); ry = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); x = rx; y = ry; } I just can't spot any difference there

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  • Generics Java and Shadowing of type parameters

    - by rubixibuc
    This code seems to work fine class Rule<T> { public <T>Rule(T t) { } public <T> void Foo(T t) { } } Does the method type parameter shadow the class type parameter? Also when you create an object does it use the type parameter of the class? example Rule<String> r = new Rule<String>(); Does this normally apply to the type parameter of the class, in the situation where they do not conflict? I mean when only the class has a type parameter, not the constructor, or does this look for a type parameter in the constructor? If they do conflict how does this change? SEE DISCUSSION BELOW if I have a function call x = <Type Parameter>method(); // this is a syntax error even inside the function or class ; I must place a this before it, why is this, and does everything still hold true. Why don't I need to prefix anything for the constructor call. Shouldn't Oracle fix this.

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  • Java How to find a value in a linked list iteratively and recursively

    - by Roxy
    Hi I have a method that has a reference to a linked list and a int value. So, this method would count and return how often the value happens in the linked list. So, I decided to make a class, public class ListNode{ public ListNode (int v, ListNode n) {value = v; next = n;) public int value; public ListNode next; } Then, the method would start with a public static int findValue(ListNode x, int valueToCount){ // so would I do it like this?? I don't know how to find the value, // like do I check it? for (int i =0; i< x.length ;i++){ valueToCount += valueToCount; } So, I CHANGED this part, If I did this recursively, then I would have public static int findValue(ListNode x, int valueToCount) { if (x.next != null && x.value == valueToCount { return 1 + findValue(x, valueToCount);} else return new findvalue(x, valueToCount); SO, is the recursive part correct now?

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  • removing the first value in an array c# or java

    - by MrCode
    hey there i was working on a program and was thinking is it possible was to remove the value from the first element in an array. Has anyone any ideas on how this could be done ? thanks for all input is much appreciated. i have only tried removing from the last element wasnt sure on how i would remove the first this is how i done the last element try { if (isEmpty()) { throw new Exception("list is empty"); } size = size -1; return values[size]; } catch(Exception e) { System.out.println(e); return -1; }

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  • Java split is eating my characters.

    - by Fenris_uy
    Hi, I have a string like this String str = "la$le\$li$lo". I want to split it to get the following output "la","le\$li","lo". The \$ is a $ escaped so it should be left in the output. But when I do str.split("[^\\\\]\\$") y get "l","le\$l","lo". From what I get my regex is matching a$ and i$ and removing then. Any idea of how to get my characters back? Thanks

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  • Big-Oh running time of code in Java (are my answers accurate

    - by Terry Frederick
    the Method hasTwoTrueValues returns true if at least two values in an array of booleans are true. Provide the Big-Oh running time for all three implementations proposed. // Version 1 public boolean has TwoTrueValues( boolean [ ] arr ) { int count = 0; for( int i = 0; i < arr. length; i++ ) if( arr[ i ] ) count++; return count >= 2; } // Version 2 public boolean hasTwoTrueValues( boolean [ ] arr ) { for( int i = 0; i < arr.length; i++ ) for( int j = i + 1; j < arr.length; j++ ) if( arr[ i ] && arr[ j ] ) return true; } // Version 3 public boolean hasTwoTrueValues( boolean [ ] arr ) { for( int i = 0; i < arr.length; i++ if( arr[ i ] ) for( int j = i + 1; j < arr.length; j++ ) if( arr[ j ] ) return true; return false; } For Version 1 I say the running time is O(n) Version 2 I say O(n^2) Version 3 I say O(n^2) I am really new to this Big Oh Notation so if my answers are incorrect could you please explain and help.

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