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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 : 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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  • 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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  • 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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  • 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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  • 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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  • java oracle cusor is closed where cursor is not return to jdbc

    - by optimus
    I am executing a stored procedure which has 2 cusors within the stored procedure. The 1st cursor which is not return to the jdbc as a resultset is closed within the stored procedure. The 2nd cursor which returns the resultset to the jdbc is not closed within the stored procedure. Upon executing I encounter cursor is closed exception which is puzzling. Since the ResultSet will close all underlying cursor upon invoking the close() method

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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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  • 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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  • Java - How to pass a Generic parameter as Class<T> to a constructor

    - by Joe Almore
    I have a problem here that still cannot solve, the thing is I have this abstract class: public abstract class AbstractBean<T> { private Class<T> entityClass; public AbstractBean(Class<T> entityClass) { this.entityClass = entityClass; }... Now I have another class that inherits this abstract: @Stateless @LocalBean public class BasicUserBean<T extends BasicUser> extends AbstractBean<T> { private Class<T> user; public BasicUserBean() { super(user); // Error: cannot reference user before supertype contructor has been called. } My question is how can I make this to work?, I am trying to make the class BasicUserBean inheritable, so if I have class PersonBean which inherits BasicUserBean then I could set in the Generic the entity Person which also inherits the entity BasicUser. And it will end up being: @Stateless @LocalBean public class PersonBean extends BasicUserBean<Person> { public PersonBean() { super(Person.class); } ... I just want to inherit the basic functionality from BasicUserBean to all descendants, so I do not have to repeat the same code among all descendants. Thanks!.

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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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  • 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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  • 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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  • Convert any object to pretty HTML in java

    - by ripper234
    How can I convert a given object (in a generic way with reflection) to pretty printable HTML? What ready made library do you recommend that does this? I need support for simple nested objects (as long as they don't create loops in the object graph). I tried to convert it to JSON, but DefaultPrettyPrinter is not HTML friendly.

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  • Web Service Security java

    - by WhoAmI
    My web service was created some time back using IBM JAX-RPC. As a part of enhancement, I need to provide some security to the existing service. One way is to provide a handler, all the request and response will pass through that handler only. In the request I can implement some authentication rules for each and every application/user accessing it. Other than this, What are the possible ways for securing it? I have heard someting called wsse security for web service. Is it possible to implement it for the JAX-RPC? Or it can be implemented only for JAX-WS? Need some helpful inputs on the wsse security so that i can jump learning it. Other than handler and wsse security, any other possible way to make a service secure? Please help.

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  • Java print binary number using bit-wise operator

    - by user69514
    Hi I am creating a method that will take a number and print it along with its binary representation. The problems is that my method prints all 0's for any positive number, and all 1's for any negative number private static void display( int number ){ System.out.print(number + "\t"); int mask = 1 << 31; for(int i=1; i<=32; i++) { if( (mask & number) != 0 ) System.out.print(1); else System.out.print(0); if( (i % 4) == 0 ) System.out.print(" "); } }

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  • Java overloading and overriding

    - by Padmanabh
    We always say that method overloading is static polymorphism and overriding is runtime polymorphism. What exactly do we mean by static here? Is the call to a method resolved on compiling the code? So whats the difference between normal method call and calling a final method? Which one is linked at compile time?

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  • 2 bucks for !! java basic question

    - by Max
    How can I get a specific value from an object? I'm trying to get a value of an instance for eg. ListOfPpl newListOfPpl = new ListOfPpl(id, name, age); Object item = newListOfPpl; How can I get a value of name from an Object item?? Even if it is easy or does not interest you can anyone help me?? Edited: I was trying to build a binary tree contains the node of ListOfPpl, and need to sort it in the lexicographic. Here's my code for insertion on the node. Any clue?? public void insert(Object item){ Node current = root; Node follow = null; if(!isEmpty()){ root = new Node(item, null, null); return; }boolean left = false, right = false; while(current != null){ follow = current; left = false; right = false; //I need to compare and sort it if(item.compareTo(current.getFighter()) < 0){ current = current.getLeft(); left = true; }else { current = current.getRight(); right = true; } }if(left) follow.setLeft(new Node(item, null, null)); else follow.setRight(new Node(item, null, null)); }

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