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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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  • Adding instances of a class to an Arraylist in java

    - by Olga
    I have 10 instances of the class movie which I wish to add to an Arraylist named Catalogue1 in a class containing a main method I write the following ArrayList catalogue1= new ArrayList () //the class movie is defined in another class Movie movie1= new Movie () Movie movie2= new Movie () Catalogue.Add (1, movie1) What is wrong? Should I define somewhere what kind of Objects this arraylist named catalogue should contain? Thank you in advance

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  • Java Trying to get a line of source from a website

    - by dsta
    I'm trying to get one line of source from a website and then I'm returning that line back to main. I keep on getting an error at the line where I define InputStream in. Why am I getting an error at this line? public class MP3LinkRetriever { private static String line; public static void main(String[] args) { String link = "www.google.com"; String line = ""; while (link != "") { link = JOptionPane.showInputDialog("Please enter the link"); try { line = Connect(link); } catch(Exception e) { } JOptionPane.showMessageDialog(null, "MP3 Link: " + parseLine(line)); String text = line; Toolkit.getDefaultToolkit( ).getSystemClipboard() .setContents(new StringSelection(text), new ClipboardOwner() { public void lostOwnership(Clipboard c, Transferable t) { } }); JOptionPane.showMessageDialog(null, "Link copied to your clipboard"); } } public static String Connect(String link) throws Exception { String strLine = null; InputStream in = null; try { URL url = new URL(link); HttpURLConnection uc = (HttpURLConnection) url.openConnection(); in = new BufferedInputStream(uc.getInputStream()); Reader re = new InputStreamReader(in); BufferedReader r = new BufferedReader(re); int index = -1; while ((strLine = r.readLine()) != null && index == -1) { index = strLine.indexOf("<source src"); } } finally { try { in.close(); } catch (Exception e) { } } return strLine; } public static String parseLine(String line) { line = line.replace("<source", ""); line = line.replace(" src=", ""); line = line.replace("\"", ""); line = line.replace("type=", ""); line = line.replace("audio/mpeg", ""); line = line.replace(">", ""); return line; } }

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  • java number exceeds long.max_value - how to detect?

    - by jurchiks
    I'm having problems detecting if a sum/multiplication of two numbers exceeds the maximum value of a long integer. Example code: long a = 2 * Long.MAX_VALUE; System.out.println("long.max * smth > long.max... or is it? a=" + a); This gives me -2, while I would expect it to throw a NumberFormatException... Is there a simple way of making this work? Because I have some code that does multiplications in nested IF blocks or additions in a loop and I would hate to add more IFs to each IF or inside the loop. Edit: oh well, it seems that this answer from another question is the most appropriate for what I need: http://stackoverflow.com/a/9057367/540394 I don't want to do boxing/unboxing as it adds unnecassary overhead, and this way is very short, which is a huge plus to me. I'll just write two short functions to do these checks and return the min or max long. Edit2: here's the function for limiting a long to its min/max value according to the answer I linked to above: /** * @param a : one of the two numbers added/multiplied * @param b : the other of the two numbers * @param c : the result of the addition/multiplication * @return the minimum or maximum value of a long integer if addition/multiplication of a and b is less than Long.MIN_VALUE or more than Long.MAX_VALUE */ public static long limitLong(long a, long b, long c) { return (((a > 0) && (b > 0) && (c <= 0)) ? Long.MAX_VALUE : (((a < 0) && (b < 0) && (c >= 0)) ? Long.MIN_VALUE : c)); } Tell me if you think this is wrong.

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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 convert JSONObject to URL parameter

    - by Alex Ivasyuv
    What is the elegant way to convert JSONObject to URL parameters. For example, JSONObject: {stat: {123456: {x: 1, y: 2}, 123457: {z: 5, y: 2}}}} this should be like: stat[123456][x]=1&stat[123456][y]=2&stat[123457][z]=5&stat[123457][y]=2 of course with escaped symbols, and of course JSON object could be more complicated.. Maybe there already exist some mechanisms for that? Thanks,

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  • Simplest way of creating java next/previous buttons

    - by Holly
    I know that when creating buttons, like next and previous, that the code can be somewhat long to get those buttons to function. My professor gave us this example to create the next button: private void jbtnNext_Click() { JOptionPane.showMessageDialog(null, "Next" ,"Button Pressed", JOptionPane.INFORMATION_MESSAGE); try { if (rset.next()) { fillTextFields(false); }else{ //Display result in a dialog box JOptionPane.showMessageDialog(null, "Not found"); } } catch (SQLException ex) { ex.printStackTrace(); } } Though, I do not really understand how that short and simple if statement is what makes the next button function. I see that the fillTextFields(false) uses a boolean value and that you need to initialize that boolean value in the beginning of the code I believe. I had put private fillTextFields boolean = false; but this does not seem to be right... I'm just hoping someone could explain it better. 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 multiple Images Uploader

    - by Padur
    Hello Folks I have this new requirement to develop a software which is a large scale image up loader in a web application. I was able to do the same using swing contains several feature like drag and drop, progress bar, remove file / files , modify, limit file size, verify file information, timer, verify at run time ..and its a very powerful tool which uploads images. I would like to do the same in web based app, like user selects 200 images process it and click upload and it should start uploading, like to know any feasible frameworks or any API's which help me do this faster and achieve the same kind of functionality. Please point me in correct direction. -PD

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  • What is the purpose of Finalization in java?

    - by Karthik
    Different websites are giving different opinions. My understanding is this: To clean up or reclaim the memory that an object occupies, the Garbage collector comes into action. (automatically is invoked???) The garbage collector then dereferences the object. Sometimes, there is no way for the garbage collector to access the object. Then finalize is invoked to do a final clean up processing after which the garbage collector can be invoked. is this right?

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  • assign keys for combo box in java

    - by adesh kumar
    I want to add a JComboBox in Swing that is simple but I want to assign the values for each items in combo. I have the following code JComboBox jc1= new JComboBox(); jc1.addItem("a"); jc1.addItem("b"); jc1.addItem("c"); Now what I want is that when click on combo box it should return 1, 2 and 3 correspondingly instead of a ,b, c. Is there any way to assign the key values for each items in combo box?

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  • Java Counting # of occurrences of a word in a string

    - by Doug
    I have a large text file I am reading from and I need to find out how many times some words come up. For example, the word "the". I'm doing this line by line each line is a string. I need to make sure that I only count legit "the"'s the the in other would not count. This means I know I need to use regular expressions in some way. What I was trying so far is this: numSpace += line.split("[^a-z]the[^a-z]").length; I realize the regular expression may not be correct at the moment but I tried without that and just tried to find occurrences of the word the and I get wrong numbers to. I was under the impression this would split the string up into an array and how many times that array was split up was how many times the word is in the string. Any ideas I would be grateful.

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  • how can i acess a variable outside of an if statement in java

    - by themanepalli
    i have defined a variable inside an if statement and I am trying to access it outside of that if statement now. now the error is saying that it cannot find the symbol which is because its being defined as an intance variable, is there a way i can change it so i can access it outside the variable? heres the code if((e.getSource()==userOrder2)&& (orderType==1)) { String buyO= userOrder2.getText(); int buyOrder= Integer.parseInt(buyO); //variable im trying to access } // trying to use buyOrder in a different if statement if(orderType==1 && (stockPrice <= buyOrder)) { orderResult.setText("The Stock" + (stockName2.getText()) + "was bought at" + stockPrice); }

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  • Embeddable database better than SQLite for java

    - by dexter
    I am creating a web application that is accessing a SQLite database in the server. I also have "clients" that updates this same database. As we know SQLite locks the entire database during INSERTs which are done by the clients and the web application is also trying to make some UPDATEs at the same time. So my problem now is about concurrency in database access. I would like to use an embeddable database like SQLite. Any suggestions.

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  • Is an ArrayList automaticaly declared static ,if it is an instance variable?(Java)

    - by Alex
    Hy ,what i`m trying to do is something like this: private class aClass { private ArrayList idProd; aClass(ArrayList prd) { this.idProd=new ArrayList(prd); } public ArrayList getIdProd() { return this.idProd; } } So if i have multiple instances of ArrayLIst (st1 ,st2 ,st3) and I want to make new objects of aClass : { aClass obj1,obj2,obj3; obj1=new aClass(st1); obj2=new aClass(st2); obj3=new aClass(st3); }why all of the aClass objects will return st3 if I access the method getIdProd() for each of them(obj1..obj3)? is an arraylist as a instance variable automatically declared static?

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  • Java JSpinner Prevent Letter Insertion

    - by asmo
    A JSpinner is used to store a number in my application (with a SpinnerNumberModel). As expected, the spinner doesn't allow invalid characters (letters, symbols, etc.) to be stored. However, those characters do appear in the spinner component when I type them in. As soon as I switch the focus to another component, they disappear. Is there a way to prevent invalid characters from appearing in the spinner?

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  • Java do while, while

    - by Pindatjuh
    Hello, what behaviour can I expect when I run this code: do while(testA) { // do stuff } while(testB); Will it behave like: do { while(testA) { // do stuff } } while(testB); Or: if(testA) { do { // do stuff } while(testA && testB); } Or something totally unexpected? I ask this question because I think this is quite ambiguous, and for other people searching on this topic, not because I am lazy to test it out.

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