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  • Java String.indexOf and empty Strings

    - by tmeisenh
    I'm curious why the String.indexOf is returning a 0 (instead of -1) when asking for the index of an empty string within a string. The Javadocs only say this method returns the index in this String of the specified string, -1 if the string isn't found. System.out.println("FOO".indexOf("")); // outputs 0 wtf!!! System.out.println("FOO".indexOf("bar")); // outputs -1 as expected System.out.println("FOO".indexOf("F")); // outputs 0 as expected System.out.println("".indexOf("")); // outputs 0 as expected, I think

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  • How to simulate an unhandled exception in Java

    - by Martin Wiboe
    Hi, I am creating some multi-threaded code, and I have created a JobDispatcher class that creates threads. I want this object to handle any unhandled exceptions in the worker threads, and so I am using Thread.setUncaughtExceptionHandler(this); Now, I would like to test this functionality - how can I generate an unhandled exception in the run() method of my worker object? Thanks, Martin

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  • Java Incompatible Types Boolean Int

    - by ikurtz
    i have the following class: public class NewGameContract { public boolean HomeNewGame = false; public boolean AwayNewGame = false; public boolean GameContract(){ if (HomeNewGame && AwayNewGame){ return true; } else { return false; } } } when i try to use it like so: if (networkConnection){ connect4GameModel.newGameContract.HomeNewGame = true; boolean status = connect4GameModel.newGameContract.GameContract(); switch (status){ case true: break; case false: break; } return; } i am getting the error: incompatible types found: boolean required: int on the following switch (status) code. what am i doing wrong please?

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  • Java method keyword "final" and its use

    - by Lukas Eder
    When I create complex type hierarchies (several levels, several types per level), I like to use the final keyword on methods implementing some interface declaration. An example: interface Garble { int zork(); } interface Gnarf extends Garble { /** * This is the same as calling {@link #zblah(0)} */ int zblah(); int zblah(int defaultZblah); } And then abstract class AbstractGarble implements Garble { @Override public final int zork() { ... } } abstract class AbstractGnarf extends AbstractGarble implements Gnarf { // Here I absolutely want to fix the default behaviour of zblah // No Gnarf shouldn't be allowed to set 1 as the default, for instance @Override public final int zblah() { return zblah(0); } // This method is not implemented here, but in a subclass @Override public abstract int zblah(int defaultZblah); } I do this for several reasons: It helps me develop the type hierarchy. When I add a class to the hierarchy, it is very clear, what methods I have to implement, and what methods I may not override (in case I forgot the details about the hierarchy) I think overriding concrete stuff is bad according to design principles and patterns, such as the template method pattern. I don't want other developers or my users do it. So the final keyword works perfectly for me. My question is: Why is it used so rarely in the wild? Can you show me some examples / reasons where final (in a similar case to mine) would be very bad?

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  • Java BufferedReader readline blocking?

    - by tgguy
    I want to make an HTTP request and then get the response as sketched here: URLConnection c = new URL("http://foo.com").openConnection(); c.setDoOutput(true); /* write an http request here using a new OutputStreamWriter(c.getOutputStream) */ BufferedReader reader = new BufferedReader(new InputStreamReader(c.getInputStream)); reader.readLine(); But my question is, if the request I send takes a long time before a response is received, what happens in the call reader.readLine() above? Will this process stay running/runnable on the CPU or will it get taken off the CPU and be notified to wake up and run again when there is IO to be read? If it stays on the CPU, what can be done to make it get off and be notified later?

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  • Implementing Java Priority Queue

    - by Kay
    public class PriorityQueue<T> { private PriorityNode<T> head, tail; private int numItems; public PriorityQueue(){ numItems = 0; head=null; tail=null; } public void add(int priority, T value){ PriorityNode<T> newNode = new PriorityNode<T>(priority,value); if(numItems == 0){ head = newNode; tail = newNode; } else{ head.setNext(newNode); head = newNode; } } } Where PriorityNode is defined as: public class PriorityNode<T> implements Comparable<T> { private T value; private PriorityNode<T> next; private int priority; public PriorityNode(int priority,T newValue){ value = newValue; next = null; priority = 0; } public PriorityNode(T newValue){ value = newValue; next = null; priority = 0; } public void setPriority(int priority){ this.priority = priority; } public int getPriority(){ return this.priority; } public T getValue(){ return value; } public PriorityNode<T> getNext(){ return next; } public void setNext(PriorityNode<T> nextNode){ this.next = nextNode; } public void setValue(T newValue){ value = newValue; } public int compareTo(int pri) { // TODO Auto-generated method stub if(this.priority<pri){ return -1; } else if(this.priority == pri){ return 0; } else{ return 1; } } } I'm having a lot of difficulty using the Comparator here and implementing a priority queue - please point me in the right direction.

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  • How to effectively copy an array in java ?

    - by Tony
    The toArray method in ArrayList , Bloch uses both System.arraycopy and Arrays.copyOf to copy an array . public <T> T[] toArray(T[] a) { if (a.length < size) // Make a new array of a's runtime type, but my contents: return (T[]) Arrays.copyOf(elementData, size, a.getClass()); System.arraycopy(elementData, 0, a, 0, size); if (a.length > size) a[size] = null; return a; } How to compare these two copy method , when to use which ? Thanks.

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  • Java multiple connections downloading file

    - by weulerjunior
    Hello friends, I was wanting to add multiple connections in the code below to be able to download files faster. Could someone help me? Thanks in advance. public void run() { RandomAccessFile file = null; InputStream stream = null; try { // Open connection to URL. HttpURLConnection connection = (HttpURLConnection) url.openConnection(); // Specify what portion of file to download. connection.setRequestProperty("Range", "bytes=" + downloaded + "-"); // Connect to server. connection.connect(); // Make sure response code is in the 200 range. if (connection.getResponseCode() / 100 != 2) { error(); } // Check for valid content length. int contentLength = connection.getContentLength(); if (contentLength < 1) { error(); } /* Set the size for this download if it hasn't been already set. */ if (size == -1) { size = contentLength; stateChanged(); } // Open file and seek to the end of it. file = new RandomAccessFile("C:\\"+getFileName(url), "rw"); file.seek(downloaded); stream = connection.getInputStream(); while (status == DOWNLOADING) { /* Size buffer according to how much of the file is left to download. */ byte buffer[]; if (size - downloaded > MAX_BUFFER_SIZE) { buffer = new byte[MAX_BUFFER_SIZE]; } else { buffer = new byte[size - downloaded]; } // Read from server into buffer. int read = stream.read(buffer); if (read == -1) { break; } // Write buffer to file. file.write(buffer, 0, read); downloaded += read; stateChanged(); } /* Change status to complete if this point was reached because downloading has finished. */ if (status == DOWNLOADING) { status = COMPLETE; stateChanged(); } } catch (Exception e) { error(); } finally { // Close file. if (file != null) { try { file.close(); } catch (Exception e) { } } // Close connection to server. if (stream != null) { try { stream.close(); } catch (Exception e) { } } } }

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  • is this possible in java or any other programming language

    - by drake
    public abstract class Master { public void printForAllMethodsInSubClass() { System.out.println ("Printing before subclass method executes"); } } public class Owner extends Master { public void printSomething () { System.out.println ("This printed from Owner"); } public int returnSomeCals () { return 5+5; } } Without messing with methods of subclass...is it possible to execute printForAllMethodsInSubClass() before the method of a subclass gets executed?

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  • Static variables in Java for a test oObject creator

    - by stevebot
    Hey, I have something like the following TestObjectCreator{ private static Person person; private static Company company; static { person = new Person() person.setName("Joe"); company = new Company(); company.setName("Apple"); } public Person createTestPerson(){ return person; } public Person createTestCompany(){ return company; } } By applying static{} what am I gaining? I assume the objects are singletons as a result. However, if I did the following: Person person = TestObjectCreator.createTestPerson(); person.setName("Jill"); Person person2 = TestObjectCreator.createTestPerson(); would person2 be named Jill or Joe?

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  • W3C dom api in Java, get child elements by name

    - by Benju
    I just realized that the method Element.getElementsByTagName("someTagName") returns a nodelist of all elements in the document that have a given tagname. What if I just want to get all child elements by tag name? For example... <person> <name>Bob</name> <car> <name>Toyota Corolla</name> </car> </person>

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  • Java Scanner won't follow file

    - by Steve Renyolds
    Trying to tail / parse some log files. Entries start with a date then can span many lines. This works, but does not ever see new entries to file. File inputFile = new File("C:/test.txt"); InputStream is = new FileInputStream(inputFile); InputStream bis = new BufferedInputStream(is); //bis.skip(inputFile.length()); Scanner src = new Scanner(bis); src.useDelimiter("\n2010-05-01 "); while (true) { while(src.hasNext()){ System.out.println("[ " + src.next() + " ]"); } } Doesn't seem like Scanner's next() or hasNext() detects new entries to file. Any idea how else I can implement, basically, a tail -f with custom delimiter. ok - using Kelly's advise i'm checking & refreshing the scanner, this works. Thank you !! if anyone has improvement suggestions plz do! File inputFile = new File("C:/test.txt"); InputStream is = new FileInputStream(inputFile); InputStream bis = new BufferedInputStream(is); //bis.skip(inputFile.length()); Scanner src = new Scanner(bis); src.useDelimiter("\n2010-05-01 "); while (true) { while(src.hasNext()){ System.out.println("[ " + src.next() + " ]"); } Thread.sleep(50); if(bis.available() > 0){ src = new Scanner(bis); src.useDelimiter("\n2010-05-01 "); } }

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  • trace this java method

    - by Bader
    public static int ABC(int x, int y) { if(y==0) return(0); else return(x + ABC(x,y-1)); } /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub System.out.println(ABC(5,3)); }

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  • Java 1.5.0_16 corrupted colours when saving jpg image

    - by Coder
    Hi, i have a loaded image from disk (stored as a BufferedImage), which i display correctly on a JPanel but when i try to re-save this image using the command below, the image is saved in a reddish hue. ImageIO.write(image, "jpg", fileName); Note! image is a BufferedImage and fileName is a File object pointing to the filename that will be saved which end in ".jpg". I have read that there were problems with ImageIO methods in earlier JDKs but i'm not on one of those versions as far as i could find. What i am looking for is a way to fix this issue without updating the JDK, however having said that i would still like to know in what JDK this issue was fixed in (if it indeed is still a bug with the JDK i'm using). Thanks.

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  • Java: Combine 2 List <String[]>

    - by battousai622
    I have two List of array string. I want to be able to create a New List (newList) by combining the 2 lists. But it must meet these 3 conditions: 1) Copy the contents of store_inventory into newList. 2) Then if the item names in store_inventory & new_acquisitions match, just add the two quantities together and change it in newList. 3) If new_acquisitions has a new item that does not exist in store_inventory, then add it to the newList. The titles for the CSV list are: Item Name, Quantity, Cost, Price. The List contains an string[] of item name, quantity, cost and price for each row. CSVReader from = new CSVReader(new FileReader("/test/new_acquisitions.csv")); List <String[]> acquisitions = from.readAll(); CSVReader to = new CSVReader(new FileReader("/test/store_inventory.csv")); List <String[]> inventory = to.readAll(); List <String[]> newList; Any code to get me started would be great! =] this is what i have so far... for (int i = 0; i < acquisitions.size(); i++) { temp1 = acquisitions.get(i); for (int j = 1; j < inventory.size(); j++) { temp2 = inventory.get(j); if (temp1[0].equals(temp2[0])) { //if match found... do something? //break out of loop } } //if new item found... do something? }

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  • Simple way to repeat a String in java

    - by e5
    I'm looking for a simple commons method or operator that allows me to repeat some String n times. I know I could write this using a for loop, but I wish to avoid for loops whenever necessary and a simple direct method should exist somewhere. String str = "abc"; String repeated = str.repeat(3); repeated.equals("abcabcabc"); Related to: repeat string javascript Create NSString by repeating another string a given number of times Edited I try to avoid for loops when they are not completely necessary because: They add to the number of lines of code even if they are tucked away in another function. Someone reading my code has to figure out what I am doing in that for loop. Even if it is commented and has meaningful variables names, they still have to make sure it is not doing anything "clever". Programmers love to put clever things in for loops, even if I write it to "only do what it is intended to do", that does not preclude someone coming along and adding some additional clever "fix". They are very often easy to get wrong. For loops that involving indexes tend to generate off by one bugs. For loops often reuse the same variables, increasing the chance of really hard to find scoping bugs. For loops increase the number of places a bug hunter has to look.

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  • Need help with using regular expression in Java

    - by richard
    Hi, I am trying to match pattern like '@(a-zA-Z0-9)+ " but not like 'abc@test'. So this is what I tried: Pattern MY_PATTERN = Pattern.compile("\\s@(\\w)+\\s?"); String data = "[email protected] #gogasig @jytaz @tibuage"; Matcher m = MY_PATTERN.matcher(data); StringBuffer sb = new StringBuffer(); boolean result = m.find(); while(result) { System.out.println (" group " + m.group()); result = m.find(); } But I can only see '@jytaz', but not @tibuage. How can I fix my problem? Thank you.

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  • debugging scaffolding contingent upon degbugging boolean (java)

    - by David
    Recently i've found myself writing a lot of methods with what i can only think to call debugging scaffolding. Here's an example: public static void printArray (String[] array, boolean bug) { for (int i = 0; i<array.lenght; i++) { if (bug) System.out.print (i) ; //this line is what i'm calling the debugging scaffolding i guess. System.out.println(array[i]) ; } } in this method if i set bug to true, wherever its being called from maybe by some kind of user imput, then i get the special debugging text to let me know what index the string being printed as at just in case i needed to know for the sake of my debugging (pretend a state of affairs exists where its helpful). All of my questions more or less boil down to the question: is this a good idea? but with a tad bit more objectivity: Is this an effective way to test my methods and debug them? i mean effective in terms of efficiency and not messing up my code. Is it acceptable to leave the if (bug) stuff ; code in place after i've got my method up and working? (if a definition of "acceptability" is needed to make this question objective then use "is not a matter of programing controversy such as ommiting brackets in an if(boolean) with only one line after it, though if you've got something better go ahead and use your definition i won't mind) Is there a more effective way to accomplish the gole of making debugging easier than what i'm doing? Anything you know i mean to ask but that i have forgotten too (as much information as makes sense is appreciated).

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