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  • Can i query a List? Java

    - by Nitesh Panchal
    Hello, Say i have List<SomeObject> objList = new ArrayList<SomeObject>(); If someObject contains a field named id. Can we find it through some query like objList.filter('id=2'); wihout looping through the list? If not, then why? This can be so useful method and used as an alternative to write tedious for loop? Just a question that came to my mind so i thought i must clear it here :) 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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  • 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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  • 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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  • Why does (360 / 24) / 60 = 0 ... in Java

    - by Ankur
    I am trying to compute (360 / 24) / 60 I keep getting the answer 0.0 when I should get 0.25 In words: I want to divide 360 by 24 and then divide the result by 60 public class Divide { public static void main(String[] args){ float div = ((360 / 24) / 60); System.out.println(div); } } This prints out: 0.0 Why is that? Am I doing something really stupid, or is there a good reason for this

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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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  • 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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  • 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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  • 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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  • Converting Java code block to Objective-C

    - by user1123688
    I am trying to convert my Android app to iOS. This will be my first iOS app. I can't seem to translate this code properly. If someone wouldn't mind showing me how its done, that would be greatly appreciated. //scrambBase20 is a Byte array String descramble(String input){ char[] ret; ret = input.toCharArray(); int offset = -scrambBase20.length; for(int i=0;i<input.length();i++){ if(i%scrambBase20.length==0) offset+=scrambBase20.length; ret[scrambBase20[i%scrambBase20.length]+offset]=(char) ((byte) (input.charAt(i))^0x45); } String realRet = ""; for (char x : ret){ realRet+=x; } realRet = realRet.trim(); return realRet; }

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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: howto write equals() shorter

    - by erikb
    I get headaches when I have to write nearly 10 lines of code to say 2 Objects are equal, when their type is equal and both's attribute is equal. You can easily see that in this way of writing the number of lines increase drastically with your number of attributes. public class Id implements Node { private String name; public Id(String name) { this.name = name; } public boolean equals(Object o) { if (o == null) return false; if (null == (Id) o) return false; Id i = (Id) o; if ((this.name != null && i.name == null) || (this.name == null && i.name != null)) return false; return (this.name == null && i.name == null) || this.name.equals(i.name); } }

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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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  • startsWith using error in java

    - by user1838839
    defined variable: LinkedList list1=new LinkedList(); Object get() in list1 obtains a node of list1 Object remove() in list1 deletes a node of list1 count() is length of list1 for(int i=1;i<list1.count();i++){ if(list1.get(i).startsWith('"',0)) //Error here list1.remove(i); } Error: cannot find symbol symbol: method charAt(int) location: class Object how to fix this problem? I would like to delete the node in list1 which starts with (").

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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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  • concatenation output problem (toString Array) - java

    - by dowln
    Hello, I am trying to display the output as "1(10) 2(23) 3(29)" but instead getting output as "1 2 3 (10)(23)(29)". I would be grateful if someone could have a look the code and possible help me. I don't want to use arraylist. the code this // int[] Groups = {10, 23, 29}; in the constructor public String toString() { String tempStringB = ""; String tempStringA = " "; String tempStringC = " "; for (int x = 1; x<=3; x+=1) { tempStringB = tempStringB + x + " "; } for(int i = 0; i < Group.length;i++) { tempStringA = tempStringA + "(" + Groups[i] + ")"; } tempStringC = tempStringB + tempStringA; return tempStringC; }

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