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  • Reverse a given sentence in java

    - by giri
    This was the question asked me in amazon interview. I could not solve the problem properly, Write a program to reverse a given sentence like "This is interview question" the output must be "question interview is this".Can any tell me how to get this done? Thanks in advance

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  • Reference variable to an object instantiated/initialized in another class in Java

    - by Alex
    The reason I'm asking is because I'm getting NullPointerException. I now this is very easy but I'm pretty new programming and find this a bit confusing. So say I have initialized an object in a class and want to access that same object from another class. Like now for instance I'm working on a small Chess game, in my model Game class I have an instance of Board, an object. Board, in turn, has an array of Squares. Square[][]. Game has board, board has Square[][]. Now if I want to access the Square[][] through the object board (in Game) of type Board. Do I just declare a variable with the same name and type or do I have to initialize it again? Board board OR Board board = new Board(); Note, I have already initialized board in the class Game so if I do it again, won't they be two totally different Board objects?

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  • Question About Eclipse Java Debugger Conditional Breakpoints Inefficiency

    - by Personman
    I just set a conditional breakpoint in Eclipse's debugger with a mildly inefficient condition by breakpoint standards - checking whether a HashMap's value list (8 elements) contains Double.NaN. This resulted in an extremely noticeable slowdown in performance - after about five minutes, I gave up. Then I copy pasted the condition into an if statement at the exact same line, put a noop in the if, and set a normal breakpoint there. That breakpoint was reached in the expected 20-30 seconds. Is there something special that conditional breakpoints do that is different from this, or is Eclipse's implementation just kinda stupid? It seems like they could fairly easily just do exactly the same thing behind the scenes.

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  • Need Java Swing equivalent of "scrollIntoView" from Browser DOM

    - by bgould
    I have a JPanel with several levels of child components, also with a JScrollPane. I'm placing a focus listener on some of the child components to add some behavior to those components, but I would also like to have that component scroll into the JPanel's viewport when focus is gained. My question is, does anyone have a general purpose function to do this, similar to the browser DOM function "scrollIntoView"? I've tried muddling through this with various inputs to JComponent.scrollRectToVisible but I guess I haven't figured out the magic word. Thanks in advance.

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  • Trying to get focus onto JTextPane after doubleclicking on JList element (Java)

    - by Alex Cheng
    Hi all. Problem: I have the following JList which I add to the textPane, and show it upon the caret moving. However, after double clicking on the Jlist element, the text gets inserted, but the caret is not appearing on the JTextPane. This is the following code: listForSuggestion = new JList(str.toArray()); listForSuggestion.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); listForSuggestion.setSelectedIndex(0); listForSuggestion.setVisibleRowCount(visibleRowCount); listScrollPane = new JScrollPane(listForSuggestion); MouseListener mouseListener = new MouseAdapter() { @Override public void mouseClicked(MouseEvent mouseEvent) { JList theList = (JList) mouseEvent.getSource(); if (mouseEvent.getClickCount() == 2) { int index = theList.locationToIndex(mouseEvent.getPoint()); if (index >= 0) { Object o = theList.getModel().getElementAt(index); //System.out.println("Double-clicked on: " + o.toString()); //Set the double clicked text to appear on textPane String completion = o.toString(); int num= textPane.getCaretPosition(); textPane.select(num, num); textPane.replaceSelection(completion); textPane.setCaretPosition(num + completion.length()); int pos = textPane.getSelectionEnd(); textPane.select(pos, pos); textPane.replaceSelection(""); textPane.setCaretPosition(pos); textPane.moveCaretPosition(pos); } } theList.clearSelection(); Any idea on how to "de-focus" the selection on the Jlist, or make the caret appear on the JTextPane after the text insertion? I'll elaborate more if this is not clear enough. Please help, thanks!

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  • Java: How to make this Serializable?

    - by Hasslarn
    I dont know that much about Serializable, but i need this class to be. How to achieve it? package helpers; public class XY implements Comparable<XY> { public int x; public int y; public XY (int x, int y) { this.x = x; this.y = y; } public int compareTo( XY other ) { String compare1 = this.x + "-" + this.y; String compare2 = other.x + "-" + other.y; return compare1.compareTo( compare2 ); } public String toString() { return this.x + "-" + this.y; } } As of now i cant send it as an object with outputstream..I´ve tried just to implement Serializable but it doesnt do the trick!

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  • can the keyword 'this' be used in an abstract class in java

    - by Reddy
    I tried with below example, it is working fine. I expected it to pick sub-class's value since object won't be created for super class (as it is abstract). But it is picking up super class's field value only. Please help me understand what is the concepts behind this? abstract class SuperAbstract { private int a=2; public void funA() { System.out.println("In SuperAbstract: this.a "+a); } } class SubClass extends SuperAbstract { private int a=34; } I am calling new SubClass.funA(); I am expecting it to print 34, but it is printing 2.

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  • Read text file in java

    - by user326091
    Hi, I have a text file. I would like to retrieve the content from one line to another line. For example, the file may be 200K lines. I want to read the content from line 78 to line 2735. Since the file may be very large, I do not want to read the whole content into the memory. thanks Frank

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  • Deferred printing in Java

    - by Bober02
    I have a specific issue with general console printing and I was wondering whether anyone has a solution for it. I am trying to print a dataTable which would look like sth like this: Table ---------------------- Name |Surname | ---------------------- Mike |Mikhailowish| Rafaello|Mirena | and so on. In order to print the border of the bar I need to know what the maximum length of each column value is. I don't want to go through the whole database to find that out and then again to print it. I would rather like to do sth like: System.out.printLater(s); //herejust leave a pointer to a StringBuilder you will build ... s.append("--------"); ... System.out.printAllDeferred(); I understand the above is probably in 99.99999% chances impossible, but perhaps you guys have a clever way of achieving the above?

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  • can this keyword be used in an abstract class in java

    - by Reddy
    I tried with below example, it is working fine. I expected it to pick sub-class's value since object won't be created for super class (as it is abstract). But it is picking up super class's field value only. Please help me understand what is the concepts behind this? abstract class SuperAbstract { private int a=2; public void funA() { System.out.println("In SuperAbstract: this.a "+a); } } class SubClass extends SuperAbstract { private int a=34; } I am calling new SubClass.funA(); I am expecting it to print 34, but it is printing 2.

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  • Java Swing UI Changing Method

    - by vigilant
    I would like to use Swing to program a simple learning game. I am wondering what would be best way to switch between UI screens. For example, I would have a screen for the Main Menu, and then when the user presses a button on that screen, I would swap out the whole screen for a completely different one. Then, arbitrary screens can be swapped in at any moment, and all of their event handlers would be reactivated while the inactive screen's event handlers will be deactivated. What type of Swing component/control would I use for each of the 'screens'. Is this even doable?

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  • Java generics conversion

    - by LittleGreenMan
    I have build a generic datacontainer and now I want to manipulate data depending on their type. However, I get an incompatable types warning. What am I doing wrong? Type _Value; public void set(Type t) throws Exception { if (_Value instanceof Integer && t instanceof Integer) { _Value = (((Integer) t - _MinValue + getRange()) % getRange()) + _MinValue; } else if (_Value instanceof Boolean && t instanceof Boolean) { _Value = t; } else throw new Exception("Invalid type"); }

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  • How to append to an array that contains blank spaces - Java

    - by Cameron Townley
    I'm trying to append to a char[] array that contains blank spaces on the end. The char array for example contains the characters 'aaa'. When I append the first time the method functions properly and outputs 'aaabbb'. The initial capacity of the array is set to 80 or multiples of 80. The second time I try and append my output looks like"aaabbb bbb". Any psuedocode would be great.

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  • Bizzare Java invalid Assignment Operator Error

    - by Kay
    public class MaxHeap<T extends Comparable<T>> implements Heap<T>{ private T[] heap; private int lastIndex; private static final int defaultInitialCapacity = 25; public void add(T newItem) throws HeapException{ if (lastIndex < Max_Heap){ heap[lastIndex] = newItem; int place = lastIndex; int parent = (place – 1)/2; //ERROR HERE********** while ( (parent >=0) && (heap[place].compareTo(heap[parent])>0)){ T temp = heap[place]; heap[place] = heap[parent]; heap[parent] = temp; place = parent; parent = (place-1)/2; }else { throw new HeapException(“HeapException: Heap full”); } } } Eclipse complains that there is a: "Syntax error on token "Invalid Character", invalid AssignmentOperator" With the red line beneath the '(place-1)' There shouldn't be an error at all since it's just straight-forward arithmetic. Or is it not that simple?

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  • Can you help with regular expressions in Java?

    - by Matt
    I have a bunch of strings which may of may not have random symbols and numbers in them. Some examples are: contains(reserved[j])){ close(); i++){ letters[20]=word I want to find any character that is NOT a letter, and replace it with a white space, so the above examples look like: contains reserved j close i letters word What is the best way to do this?

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  • Java Disabled JLabel Reports Mouse Clicked

    - by ikurtz
    colLabels[i].addMouseListener(new MyAdapter()); private class MyAdapter extends MouseAdapter { @Override public void mouseClicked(MouseEvent event) { ColJLabel colJLabel = (ColJLabel)event.getComponent(); System.out.println(colJLabel.ColID); setColumnHeader(false); } } colLabels[i].setEnabled(flag); The situation is this: Mouse clicks are trapped correctly but when i have the JLabel (ColJLabel) control disabled it still reports mouse clicks. How can I make so that mouse clicks are only reported when the control is enabled? Thanks.

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  • Get n Number of words using regex in Java

    - by Aymon Fournier
    I have a section of a book, complete with punctuation, line breaks etc. and I want to be able to extract the first n words from the text, and divide that into 5 parts. Regex mystifies me. This is what I am trying. I creates an array of index size 0, with all the input text: public static String getNumberWords2(String s, int nWords){ String[] m = s.split("([a-zA-Z_0-9]+\b.*?)", (nWords / 5)); return "Part One: \n" + m[1] + "\n\n" + "Part Two: \n" + m[2] + "\n\n" + "Part Three: \n" + m[3] + "\n\n" + "Part Four: \n" + m[4] + "\n\n" + "Part Five: \n" + m[5]; } Thanks!

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  • What is a good "Error Checking" Pattern (Java)?

    - by Jack
    I'll explain what I mean by input error checking. Say you have a function doSomething(x). If the function completes successfully doSomething does something and returns nothing. However, if there are errors I'd like to be notified. That is what I mean by error checking. I'm looking for, in general, the best way to check for errors. I've thought of the following solutions, each with a potential problem. Flag error checking. If doSomething(x) completes successfully return null. Otherwise, it returns a boolean or an error string. Problem: Side effects. Throwing an exception. Throw an exception if doSomething(x) encounters an error. Problem: If you are performing error checking for parameters only, throwing an IllegalArgumentExceptionseems inappropriate. Validating input prior to function call. If the error checking is only meant for the parameters of the function, then you can call a validator function before calling the doSomething(x) function. Problem: What if a client of the class forgets to call the validator function before calling doSomething(x)? I often encounter this problem and any help or a point in the right direction would be much appreciated.

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