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  • Java: why is declaration not sufficient in interface?

    - by HH
    Big class contains Format-interfcase and Format-class. The Format-class contains the methods and the interface has the values of the fields. I could have the fields in the class Format but the goal is with Interface. So do I just create dummy-vars to get the errors away, design issue or something ELSE? KEY: Declaration VS Initialisation Explain by the terms, why you have to init in interface. What is the logic behind it? To which kind of problems it leads the use of interface? Sample Code having the init-interface-problem import java.util.*; import java.io.*; public class FormatBig { private static class Format implements Format { private static long getSize(File f){return f.length();} private static long getTime(File f){return f.lastModified();} private static boolean isFile(File f){if(f.isFile()){return true;}} private static boolean isBinary(File f){return Match.isBinary(f);} private static char getType(File f){return Match.getTypes(f);} private static String getPath(File f){return getNoErrPath(f);} //Java API: isHidden, --- SYSTEM DEPENDED: toURI, toURL Format(File f) { // PUZZLE 0: would Stack<Object> be easier? size=getSize(f); time=getTime(f); isfile=isFile(f); isBinary=isBinary(f); type=getType(f); path=getPath(f); //PUZZLE 1: how can simplify the assignment? values.push(size); values.push(time); values.push(isfile); values.push(isBinary); values.push(type); values.push(path); } } public static String getNoErrPath(File f) { try{return f.getCanonicalPath(); }catch(Exception e){e.printStackTrace();} } public static final interface Format { //ERR: IT REQUIRES "=" public long size; public long time; public boolean isFile=true; //ERROR goes away if I initialise wit DUMMY public boolean isBinary; public char type; public String path; Stack<Object> values=new Stack<Object>(); } public static void main(String[] args) { Format fm=new Format(new File(".")); for(Object o:values){System.out.println(o);} } }

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  • Algorithm to generate a list of unique combinations based on a list of numbers

    - by ross
    I would like to efficiently generate a unique list of combinations of numbers based on a starting list of numbers. example start list = [1,2,3,4,5] but the algorithm should work for [1,2,3...n] result = [1],[2],[3],[4],[5] [1,2],[1,3],[1,4],[1,5] [1,2,3],[1,2,4],[1,2,5] [1,3,4],[1,3,5],[1,4,5] [2,3],[2,4],[2,5] [2,3,4],[2,3,5] [3,4],[3,5] [3,4,5] [4,5] Note. I don't want duplicate combinations, although I could live with them, eg in the above example I don't really need the combination [1,3,2] because it already present as [1,2,3]

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  • Help with a sort method

    - by Capsud
    Hi there, If i have an array of strings for example Static final String[] TEST = new String[] { "g","a","b","t","e" }; How would i go about sorting this in alphabetical order please?

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  • Why am I having this InstantiationException in Java when accessing final local variables?

    - by Oscar Reyes
    I was playing with some code to make a "closure like" construct ( not working btw ) Everything looked fine but when I tried to access a final local variable in the code, the exception InstantiationException is thrown. If I remove the access to the local variable either by removing it altogether or by making it class attribute instead, no exception happens. The doc says: InstantiationException Thrown when an application tries to create an instance of a class using the newInstance method in class Class, but the specified class object cannot be instantiated. The instantiation can fail for a variety of reasons including but not limited to: - the class object represents an abstract class, an interface, an array class, a primitive type, or void - the class has no nullary constructor What other reason could have caused this problem? Here's the code. comment/uncomment the class attribute / local variable to see the effect (lines:5 and 10 ). import javax.swing.*; import java.awt.event.*; import java.awt.*; class InstantiationExceptionDemo { //static JTextField field = new JTextField();// works if uncommented public static void main( String [] args ) { JFrame frame = new JFrame(); JButton button = new JButton("Click"); final JTextField field = new JTextField();// fails if uncommented button.addActionListener( new _(){{ System.out.println("click " + field.getText()); }}); frame.add( field ); frame.add( button, BorderLayout.SOUTH ); frame.pack();frame.setVisible( true ); } } class _ implements ActionListener { public void actionPerformed( ActionEvent e ){ try { this.getClass().newInstance(); } catch( InstantiationException ie ){ throw new RuntimeException( ie ); } catch( IllegalAccessException ie ){ throw new RuntimeException( ie ); } } } Is this a bug in Java? edit Oh, I forgot, the stacktrace ( when thrown ) is: Caused by: java.lang.InstantiationException: InstantiationExceptionDemo$1 at java.lang.Class.newInstance0(Class.java:340) at java.lang.Class.newInstance(Class.java:308) at _.actionPerformed(InstantiationExceptionDemo.java:25)

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  • What does [a|b|c] evaluate to in Prolog?

    - by Ambrose
    The pipe operator in prolog returns one or more atomic Heads and a Tail list. ?- [a,b,c] = [a,b|[c]]. true. Nesting multiple pipes in a single match can be done similar to this: ?- [a,b,c] = [a|[b|[c]]]. true. What does the statement [a|b|c] infer about a, b and c?

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  • question about partition

    - by davit-datuashvili
    i have question about hoare partition method here is code and also pseudo code please if something is wrong correct pseudo code HOARE-PARTITION ( A, p, r) 1 x ? A[ p] 2 i ? p-1 3 j ? r +1 4 while TRUE 5 do repeat j ? j - 1 6 until A[ j ] = x 7 do repeat i ? i + 1 8 until A[i] = x 9 if i < j 10 then exchange A[i] ? A[ j ] 11 else return j and my code public class Hoare { public static int partition(int a[],int p,int r) { int x=a[p]; int i=p-1; int j=r+1; while (true) { do { j=j-1; } while(a[j]>=x); do { i=i+1; } while(a[i]<=x); if (i<j) { int t=a[i]; a[i]=a[j]; a[j]=t; } else { return j; } } } public static void main(String[]args){ int a[]=new int[]{13,19,9,5,12,8,7,4,11,2,6,21}; partition(a,0,a.length-1); } } and mistake is this error: Class names, 'Hoare', are only accepted if annotation processing is explicitly requested 1 error any ideas

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  • string reverse without new array

    - by Codeguru
    hi can anybody tell me the error in this? #include<stdio.h> int main() { char a[]="abcdefgh"; int i=0; int n=strlen(a); char *first; char *second; char *c; *first=a[0]; *second=a[7]; for(i=0;i<=n/2;i++) { *c=*first; *first=*second; *second=*c; first++; second--; } for(i=0;i<=7;i++) { printf("%c",a[i]); } }

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  • Why does this program stop running?

    - by designloper
    Hi everyone....I am developing a card making system...nothing fancy. Right got this far but program now stops running with no error when running after the first card sample i.e. " Enter 'OK' if this card is OK, otherwise enter an alternative border character: + ". Any suggestions Java Masters? //Ask user for input //makes use of print line method System.out.println("Enter name: "); //took the variables //called the object of the scanner 'cardOrder' //and use the Scanner objects method '.nextLine' //to read the next line of the input firstName = cardOrder.nextLine(); mInitial = cardOrder.nextLine(); lastName = cardOrder.nextLine(); //Print out the "Here is a sample card" + the first name, middle initial and last name System.out.println("Here is a sample card: \n\n" + firstName + mInitial + lastName + "**************" + "**************" + firstName + mInitial + lastName + "\n* *" + "\n*" + " " + firstName + mInitial + lastName + " *" + "\n* *\n" + firstName + mInitial + lastName +"**************" + "**************" + firstName + mInitial + lastName + "\n"); //Ask user is the card is OK to proceed to order query or if they want an alternative border character: + System.out.println("Enter 'OK' if this card is OK, otherwise enter an alternative border character: + "); //Check if user entered "OK" and store it in var optionA optionA = cardOrder.nextLine(); //test if (a == optionA){ System.out.println("\nHow many cards would you like? "); cardsOrdered = cardOrder.nextInt(); equals = (int) (cardPriceA * cardsOrdered); System.out.println("The price of " + cardsOrdered + " cards"+ " is £" + equals + ".\n"); System.out.println("No Discount given."); } else if(b == optionA) { //Print out the "Here is a sample card" + the first name, middle initial and last name System.out.println("Here is a sample card: \n\n" + firstName + mInitial + lastName + "++++++++++++++" + "++++++++++++++" + firstName + mInitial + lastName + "\n+ +" + "\n+" + " " + firstName + mInitial + lastName + " +" + "\n+ +\n" + firstName + mInitial + lastName +"++++++++++++++" + "++++++++++++++" + firstName + mInitial + lastName + "\n"); //Ask user is the card is OK to proceed to order query or if they want an alternative border character: + System.out.println("Enter 'OK' if this card is OK, otherwise enter an alternative border character: OK "); //Check if user entered "OK" and store it in var optionA optionA = cardOrder.nextLine(); if (a == optionA){ System.out.println("\nHow many cards would you like? "); cardsOrdered = cardOrder.nextInt(); equals = (int) (cardPriceA * cardsOrdered); System.out.println("The price of " + cardsOrdered + " cards"+ " is £" + equals + ".\n"); System.out.println("No Discount given."); } } else if (c == optionA) {//Print out the "Here is a sample card" + the first name, middle initial and last name System.out.println("Here is a sample card: \n\n" + firstName + mInitial + lastName + "**************" + "**************" + firstName + mInitial + lastName + "\n* *" + "\n*" + " " + firstName + mInitial + lastName + " *" + "\n* *\n" + firstName + mInitial + lastName +"**************" + "**************" + firstName + mInitial + lastName + "\n"); //Ask user is the card is OK to proceed to order query or if they want an alternative border character: + System.out.println("Enter 'OK' if this card is OK, otherwise enter an alternative border character: + "); //Check if user entered "OK" and store it in var optionA optionA = cardOrder.nextLine(); if (a == optionA){ System.out.println("\nHow many cards would you like? "); cardsOrdered = cardOrder.nextInt(); equals = (int) (cardPriceA * cardsOrdered); System.out.println("The price of " + cardsOrdered + " cards"+ " is £" + equals + ".\n"); System.out.println("No Discount given."); } }

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  • Possible SWITCH Optimization in DAX – #powerpivot #dax #tabular

    - by Marco Russo (SQLBI)
    In one of the Advanced DAX Workshop I taught this year, I had an interesting discussion about how to optimize a SWITCH statement (which could be frequently used checking a slicer, like in the Parameter Table pattern). Let’s start with the problem. What happen when you have such a statement? Sales :=     SWITCH (         VALUES ( Period[Period] ),         "Current", [Internet Total Sales],         "MTD", [MTD Sales],         "QTD", [QTD Sales],         "YTD", [YTD Sales],          BLANK ()     ) The SWITCH statement is in reality just syntax sugar for a nested IF statement. When you place such a measure in a pivot table, for every cell of the pivot table the IF options are evaluated. In order to optimize performance, the DAX engine usually does not compute cell-by-cell, but tries to compute the values in bulk-mode. However, if a measure contains an IF statement, every cell might have a different execution path, so the current implementation might evaluate all the possible IF branches in bulk-mode, so that for every cell the result from one of the branches will be already available in a pre-calculated dataset. The price for that could be high. If you consider the previous Sales measure, the YTD Sales measure could be evaluated for all the cells where it’s not required, and also when YTD is not selected at all in a Pivot Table. The actual optimization made by the DAX engine could be different in every build, and I expect newer builds of Tabular and Power Pivot to be better than older ones. However, we still don’t live in an ideal world, so it could be better trying to help the engine finding a better execution plan. One student (Niek de Wit) proposed this approach: Selection := IF (     HASONEVALUE ( Period[Period] ),     VALUES ( Period[Period] ) ) Sales := CALCULATE (     [Internet Total Sales],     FILTER (         VALUES ( 'Internet Sales'[Order Quantity] ),         'Internet Sales'[Order Quantity]             = IF (                 [Selection] = "Current",                 'Internet Sales'[Order Quantity],                 -1             )     ) )     + CALCULATE (         [MTD Sales],         FILTER (             VALUES ( 'Internet Sales'[Order Quantity] ),             'Internet Sales'[Order Quantity]                 = IF (                     [Selection] = "MTD",                     'Internet Sales'[Order Quantity],                     -1                 )         )     )     + CALCULATE (         [QTD Sales],         FILTER (             VALUES ( 'Internet Sales'[Order Quantity] ),             'Internet Sales'[Order Quantity]                 = IF (                     [Selection] = "QTD",                     'Internet Sales'[Order Quantity],                     -1                 )         )     )     + CALCULATE (         [YTD Sales],         FILTER (             VALUES ( 'Internet Sales'[Order Quantity] ),             'Internet Sales'[Order Quantity]                 = IF (                     [Selection] = "YTD",                     'Internet Sales'[Order Quantity],                     -1                 )         )     ) At first sight, you might think it’s impossible that this approach could be faster. However, if you examine with the profiler what happens, there is a different story. Every original IF’s execution branch is now a separate CALCULATE statement, which applies a filter that does not execute the required measure calculation if the result of the FILTER is empty. I used the ‘Internet Sales’[Order Quantity] column in this example just because in Adventure Works it has only one value (every row has 1): in the real world, you should use a column that has a very low number of distinct values, or use a column that has always the same value for every row (so it will be compressed very well!). Because the value –1 is never used in this column, the IF comparison in the filter discharge all the values iterated in the filter if the selection does not match with the desired value. I hope to have time in the future to write a longer article about this optimization technique, but in the meantime I’ve seen this optimization has been useful in many other implementations. Please write your feedback if you find scenarios (in both Power Pivot and Tabular) where you obtain performance improvements using this technique!

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  • Non-Blocking I/O Made Possible in Java

    Java SE7 "Dolphin" release is nearing and we're chomping at the bit. So let's dig in and review non-blocking IO, a feature of java.nio (New I/O) package that is a part of Java v1.4, v1.5 and v1.6 and we'll also take a peek at the java.nio.file (NIO.2) package.

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  • Non-Blocking I/O Made Possible in Java

    Java SE7 "Dolphin" release is nearing and we're chomping at the bit. So let's dig in and review non-blocking IO, a feature of java.nio (New I/O) package that is a part of Java v1.4, v1.5 and v1.6 and we'll also take a peek at the java.nio.file (NIO.2) package.

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  • Is it possible to get dragging work on a Macbook multi-touch touch pad

    - by lhahne
    I have a Macbook 5,1. That is to say that it is the only 13 inch aluminium Macbook as the later revisions were renamed Macbook Pro. Two-finger scrolling seems to work fine but dragging doesn't work. In OsX this works so that you point an object, click and keep your finger pressed on the touch pad while slide another finger to move the cursor. This causes weird and undefined behavior in Ubuntu as it seems the driver doesn't recognize this as dragging. Any ideas?

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  • How the "migrations" approach makes database continuous integration possible

    - by David Atkinson
    Testing a database upgrade script as part of a continuous integration process will only work if there is an easy way to automate the generation of the upgrade scripts. There are two common approaches to managing upgrade scripts. The first is to maintain a set of scripts as-you-go-along. Many SQL developers I've encountered will store these in a folder prefixed numerically to ensure they are ordered as they are intended to be run. Occasionally there is an accompanying document or a batch file that ensures that the scripts are run in the defined order. Writing these scripts during the course of development requires discipline. It's all too easy to load up the table designer and to make a change directly to the development database, rather than to save off the ALTER statement that is required when the same change is made to production. This discipline can add considerable overhead to the development process. However, come the end of the project, everything is ready for final testing and deployment. The second development paradigm is to not do the above. Changes are made to the development database without considering the incremental update scripts required to effect the changes. At the end of the project, the SQL developer or DBA, is tasked to work out what changes have been made, and to hand-craft the upgrade scripts retrospectively. The end of the project is the wrong time to be doing this, as the pressure is mounting to ship the product. And where data deployment is involved, it is prudent not to feel rushed. Schema comparison tools such as SQL Compare have made this latter technique more bearable. These tools work by analyzing the before and after states of a database schema, and calculating the SQL required to transition the database. Problem solved? Not entirely. Schema comparison tools are huge time savers, but they have their limitations. There are certain changes that can be made to a database that can't be determined purely from observing the static schema states. If a column is split, how do we determine the algorithm required to copy the data into the new columns? If a NOT NULL column is added without a default, how do we populate the new field for existing records in the target? If we rename a table, how do we know we've done a rename, as we could equally have dropped a table and created a new one? All the above are examples of situations where developer intent is required to supplement the script generation engine. SQL Source Control 3 and SQL Compare 10 introduced a new feature, migration scripts, allowing developers to add custom scripts to replace the default script generation behavior. These scripts are committed to source control alongside the schema changes, and are associated with one or more changesets. Before this capability was introduced, any schema change that required additional developer intent would break any attempt at auto-generation of the upgrade script, rendering deployment testing as part of continuous integration useless. SQL Compare will now generate upgrade scripts not only using its diffing engine, but also using the knowledge supplied by developers in the guise of migration scripts. In future posts I will describe the necessary command line syntax to leverage this feature as part of an automated build process such as continuous integration.

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  • It is possible to hibernate an LXC container?

    - by Jo-Erlend Schinstad
    I know about lxc-freeze and lxc-unfreeze, but as I understand it, these simply pauses the container, similar to sending SIGSTOP and SIGCONT to a process. If I reboot the host, then the containers will cease to exist, right? I would really like a way to save state to persistent storage so that I could resume them at some later time, even the host is rebooted or something like that. I can achieve exactly what I want using VirtualBox by using the "Save machine state" mechanism, but if I could do it with LXC, it would be completely awesome.

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  • Is it necessary to create a database with as few tables as possible

    - by Shaheer
    Should we create a database structure with a minimum number of tables? Should it be designed in a way that everything stays in one place or is it okay to have more tables? Will it in anyway affect anything? I am asking this question because a friend of mine modified some database structure in mediaWiki. In the end, instead of 20 tables he was using only 8, and it took him 8 months to do that (it was his college assignment). EDIT I am concluding the answer as: size of the tables does NOT matter, until the case is exceptional; in which case the denormalization may help. Thanks to everyone for the answers.

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