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  • Accessing variables in other classes (Java)

    - by George
    Why doesn't the following program return 0, since I am accessing p from a new A(), which has not had main called on it? public class A { public int p = 0; public static void main(String[] args) { p = Integer.parseInt(args[0]); new B().go(); } } class B { public void go() { System.out.println(new A().p); } }

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  • How to identify end of InputStream in java

    - by Vardhaman
    I am trying to read bytes from server using Socket program, ie I am using InputStream to read the bytes. If I pass the length size I am able to read the bytes, but I am not sure what may be the length. So I am not able initialize the byte array. Also I tried while (in.read() !=-1), I observered it loop works fine when the data is sent , but the next line after the loop is not executable , I feel its still looking for the data in the stream but there is no ata. If I close the Server connection , then my client will execute the next line followed to the loop. I am not sure where I am going wrong? this.in = socket.getInputStream(); int dataInt = this.in.read(); while(dataInt != -1){ System.out.print(","+i+"--"+dataInt); i++; dataInt = this.in.read(); } System.out.print("End Of loop"); I get the output as:- ,1--0,2--62,3--96,4--131,5--142,6--1,7--133,8--2,9--16,10--48,11--56,12--1,13--0,14--14,15--128,16--0,17--0,18--0,19--48,20--0,21--0,22--0,23--0,24--0,25--1,26--0,27--0,28--38,29--114,30--23,31--20,32--70,33--3,34--20,35--1,36--133,37--48,38--51,39--49,40--52,41--49,42--55,43--49,44--52,45--52,46--54,47--55,48--50,49--51,50--52,51--48,52--53,53--56,54--51,55--48,56--48,57--57,58--57,59--57,60--57,61--57,62--57,63--57,64--56 But no output for :- End Of loop Please guide how shall I close the loop? Looking forward for you response. Thanking you all in advance.

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  • Cannot create an array of LinkedLists in Java...?

    - by kchau
    I'm working on a sparse matrix class that needs to use an array of LinkedLists to store the values of a matrix. Each element of the array (i.e. each LinkedList) represents a row of the matrix. And, each element in the LinkedLists represents a column and the stored value. In my class, I have a declaration of the array as: private LinkedList<IntegerNode>[] myMatrix; And, in my constructor for the SparseMatrix, I try to define: myMatrix = new LinkedList<IntegerNode>[numRows]; The error I end up getting is "Cannot create a generic array of LinkedList<IntegerNode>." So, I have two issues with this, 1) What am I doing wrong, and 2) Why is the type acceptable in the declaration for the array if it can't be created? Edit: IntegerNode is a class that I have created. And, all of my class files are packaged together.

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  • Java getMethod with subclass parameter

    - by SelectricSimian
    I'm writing a library that uses reflection to find and call methods dynamically. Given just an object, a method name, and a parameter list, I need to call the given method as though the method call were explicitly written in the code. I've been using the following approach, which works in most cases: static void callMethod(Object receiver, String methodName, Object[] params) { Class<?>[] paramTypes = new Class<?>[params.length]; for (int i = 0; i < param.length; i++) { paramTypes[i] = params[i].getClass(); } receiver.getClass().getMethod(methodName, paramTypes).invoke(receiver, params); } However, when one of the parameters is a subclass of one of the supported types for the method, the reflection API throws a NoSuchMethodException. For example, if the receiver's class has testMethod(Foo) defined, the following fails: receiver.getClass().getMethod("testMethod", FooSubclass.class).invoke(receiver, new FooSubclass()); even though this works: receiver.testMethod(new FooSubclass()); How do I resolve this? If the method call is hard-coded there's no issue - the compiler just uses the overloading algorithm to pick the best applicable method to use. It doesn't work with reflection, though, which is what I need. Thanks in advance!

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  • Dynamic Image Caching with Java

    - by zteater
    I have a servlet with an API that delivers images from GET requests. The servlet creates a data file of CAD commands based on the parameters of the GET request. This data file is then delivered to an image parser, which creates an image on the file system. The servlet reads the image and returns the bytes on the response. All of the IO and the calling of the image parser program can be very taxing and images of around 80kb are rendering in 3-4000ms on a local system. There are roughly 20 parameters that make up the GET request. Each correlates to a different portion of the image. So, the combinations of possible images is extremely large. To alleviate the loading time, I plan to store BLOBs of rendered images in a database. If a GET request matches one previously executed, I will pull from cache. Else, I will render a new one. This does not fix "first-time" run, but will help "n+1 runs". Any other ideas on how I can improve performance?

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  • Java:How to align Jpanels

    - by John
    I have this code but it doesn't work: jPanel1.add(jLabel1); jPanel2.add(jButton1); jPanel2.add(jButton2); jPanel3.add(jPanel1,jPanel1.TOP_ALIGNMENT); jPanel3.add(jPanel2,jPanel2.BOTTOM_ALIGNMENT); setContentPane(jPanel3); pack(); Please tell me why!

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  • Why does java.util.concurrent.ArrayBlockingQueue use 'while' loops instead of 'if' around calls to

    - by theFunkyEngineer
    I have been playing with my own version of this, using 'if', and all seems to be working fine. Of course this will break down horribly if signalAll() is used instead of signal(), but if only one thread at a time is notified, how can this go wrong? Their code here - check out the put() and take() methods; a simpler and more-to-the-point implementation can be seen at the top of the JavaDoc for Condition. Relevant portion of my implementation below. public Object get() { lock.lock(); try { if( items.size() < 1 ) hasItems.await(); Object poppedValue = items.getLast(); items.removeLast(); hasSpace.signal(); return poppedValue; } catch (InterruptedException e) { e.printStackTrace(); return null; } finally { lock.unlock(); } } public void put(Object item) { lock.lock(); try { if( items.size() >= capacity ) hasSpace.await(); items.addFirst(item); hasItems.signal(); return; } catch (InterruptedException e) { e.printStackTrace(); } finally { lock.unlock(); } } P.S. I know that generally, particularly in lib classes like this, one should let the exceptions percolate up.

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  • Sending arbitrarily long string over Java TCP socket

    - by bibismcbryde
    I have an Android app that communicates over a TCP socket with a server I wrote. The method I'm using now to read and write output works fine for smaller strings (up to 60kB) but I get an exception thrown when the string is much longer than that. Here is the relevant part of what I have for the server and client: Server: DataInputStream dis = null; DataOutputStream dos = null; try { dis = new DataInputStream(server.getInputStream()); dos = new DataOutputStream(server.getOutputStream()); String input = ""; input = dis.readUTF(); handle_input info = new handle_input(input, id); String xml = info.handle(); dos.writeUTF(xml); server.close(); } Client: Socket socket = null; DataOutputStream dos = null; DataInputStream dis = null; Boolean result; try { socket = new Socket(ip, port); dos = new DataOutputStream(socket.getOutputStream()); dis = new DataInputStream(socket.getInputStream()); dos.writeUTF(the_text); String in = ""; while (in.equals("")) { in += dis.readUTF(); } } How can I modify it to deal with potentially enormous Strings? I've been looking around and can't seem to find a clear answer. Thanks.

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  • List Question in Java

    - by TiNS
    Hello All, I have a following ArrayList, [Title,Data1,Data2,Data3] [A,2,3,4] [B,3,5,7] And I would like to convert this one like this, [Title,A,B] [Data1,2,3] [Data2,3,5] [Data3,4,7] I'm bit confused with the approach. Any hint would be much appreciated. Thanks.

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  • What is the explanation of this java code ?

    - by M.H
    I have the following code : public class Main { public void method(Object o) { System.out.println("Object Version"); } public void method(String s) { System.out.println("String Version"); } public static void main(String args[]) { Main question = new Main(); question.method(null);//1 } } why is the result is "String Version" ? and why there is a compiler error if the first method takes a StringBuffer object ?

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  • Insertion into BST without header Node JAVA

    - by Petiatil
    I am working on a recursive insertion method for a BST. This function is suppose to be a recursive helper method and is in a private class called Node. The Node class is in a class called BinarySearchTree which contains an instance variable for the root. When I am trying to insert an element, I get a NullPointerException at : this.left = insert(((Node)left).element); I am unsure about why this occurs. If I understand correctly, in a BST, I am suppose to insert the item at the last spot on the path transversed. Any help is appreciated! private class Node implements BinaryNode<E> { E item; BinaryNode<E> left, right; public BinaryNode<E> insert(E item) { int compare = item.compareTo(((Node)root).item); if(root == null) { root = new Node(); ((Node)root).item = item; } else if(compare < 0) { this.left = insert(((Node)left).item); } else if(compare > 0) { this.right = insert(((Node)right).item); } return root; } }

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  • question about comlen function in java

    - by davit-datuashvili
    in c or c++ function comlen is defined such int comlen(char *p,char *q){ int i=0; while *p && (*p++==*q++) i++; return i; is this code equivalent of this function int comlen(String s,String m){ int i=0; while (i<s.length() && s.charAt(i)==m.charAt(i)){ i++; } return i; ? please help

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  • ArrayList to Array of Strings in java

    - by rajivpradeep
    ArrayList<String> newArray = new ArrayList<String>(); newArray = urlList.getUrl(); for( int i = 0 ; i < newArray.size();i++) { System.out.println(newArray.get(i)); } newArray.toArray(mStrings );// is this correct mStrings = newArray.toArray();// or this to convert ArrayList ot String array here for( int i = 0 ; i < mStrings.length;i++) { System.out.println(mStrings[i]); }

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  • java source code doubt

    - by abson
    Why is it that class swi22 { public static void main(String[] args) { int a=98; switch(a) { default:{ System.out.println("default");continue;} case 'b':{ System.out.println(a); continue;} case 'a':{ System.out.println(a);} } System.out.println("Switch Completed"); } } gives error as: continue outside of loop

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  • toString() in Java

    - by Allain Lalonde
    A lead developer on my project has taken to referring to the project's toString() implementations as "pure cruft" and is looking to remove them from the code base. I've said that doing so would mean that any clients wishing to display the objects would have to write their own code to convert the object to string, but that was answered with "yes they would". Now specifically, the objects in this system are graphic elements like rectangles, circles, etc and the current representation is to display x, y, scale, bounds, etc... So, where does the crowd lie? When should you and when shouldn't you implement toString?

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  • Java variables across methods

    - by NardCake
    I'm making a basic text editor, and I have 2 methods the first one is triggered when a user click 'Open' and it prompts the user to pick a file and it opens the file fine. I just want to access the same file path which is in a variable in the method that is triggered when the user clicks save. My methods are public, Iv'e tried accessing it through a class, still no. Please help! Code: public void open(){ try{ //Open file JFileChooser fc = new JFileChooser(); fc.showOpenDialog(null); File file = fc.getSelectedFile(); String haha = file.getPath(); BufferedReader br = new BufferedReader(new FileReader(file.getPath())); String line; while((line = br.readLine()) != null){ text.append(line + "\n"); } } catch (FileNotFoundException e){ e.printStackTrace(); }catch (IOException e){ } } public void save(){ try { BufferedWriter bw = new BufferedWriter(new FileWriter(file.filePath)); bw.write(text.getText()); bw.close(); } catch (IOException e) { e.printStackTrace(); } }

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  • How to return a string from char[] array using recursion loop.(java)

    - by Daniel
    I am very bed in recursion... I need to convert a char[] array by using recursion loop only, into string. Without using for(),while()... loops. For example if i have char array: a[0]='H', a[1]='e', a[2]='l',a[3]= 'l',a[4]= 'o', it returns H e l l o. What I doing wrong? public String toFormattedString(char[] a) { int temp =a.length; if (a == null) return "null"; if (a.length == 0) return "0"; if( a.length == 1 ) else if( a[0] == a[a.length] ) return toFormattedString (a[a.length -1])+a[a.length];

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