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  • Should i use lock.lock(): in this method?

    - by user962800
    I wrote this method whose purpose is to give notice of the fact that a thread is leaving a specific block of code A thread stands for a car which is leaving a bridge so other cars can traverse it . The bridge is accessible to a given number of cars (limited capacity) and it's one way only. public void getout(int diection){ // release the lock semaphore.release(); try{ lock.lock(); //access to shared data if(direction == Car.NORTH) nNordTraversing--; //decreasing traversing threads else nSudTraversing--; bridgeCond.signal(); }finally{ lock.unlock(); } } My question is: should I use lock.lock(); or it's just nonsense? thanks in advance

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  • calling a service layer method to my presentation layer

    - by Josepth Vodary
    Ok I feel really dumb asking this but I seem to be missing something really simple here. I have the following code in a class in my service layer - public Items getItems(String category, float amount, String color, String type) The code reads from a database and returns the results - I plan on placing it in a jframe. Nice and simple. But no matter how I call it from the jframe I get errors in eclipse that the code is wrong - either that their are illegal modifiers or such. So obviously I am calling it completely wrong, so my stupid question is how do you call that method into a jframe? For example - if I try to call it this way: public Items getItems(); I get told that getItems is an illegal parameter. If I call this.. Items getItems(); I am told its undefined

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  • Velocity Templates - New Line.

    - by LdSe
    Hello all, I've been working with Apache's Velocity engine and a custom template. The thing is, that I haven't been able to generate a String with the corresponding line breaks. I tried almost everything that I found, such as using $esc.n and $esc.newline (I'm already using escape tools on my project) but it seems that the version I'm currently using doesn't support it (1.4), checked if putting '\n', '\\n' and even '\\\n' would work, but same thing. Does anyone have any solution to this? Thanks a lot in advance! Regards.

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  • Scanner class is skipping lines

    - by user2403304
    I'm new to programing and I'm having a problem with my scanner class. This code is in a loop and when the loop comes around the second, third whatever time I have it set to it skips the first title input. I need help please why is it skipping my title scanner input in the beginning? System.out.println("Title:"); list[i].title=keyboard.nextLine(); System.out.println("Author:"); list[i].author=keyboard.nextLine(); System.out.println("Album:"); list[i].album=keyboard.nextLine(); System.out.println("Filename:"); list[i].filename=keyboard.nextLine();

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  • How do I check that an entity is unreferenced in JPA?

    - by Martin
    I have the following model @Entity class Element { @Id int id; @Version int version; @ManyToOne Type type; } @Entity class Type { @Id int id; @Version int version; @OneToMany(mappedBy="type") Collection<Element> elements; @Basic(optional=false) boolean disabled; } and would like to allow Type.disabled = true only if Type.elements is empty. Is there a way to do it atomically? I would like to prevent an insertion of an Element in a transaction while the corresponding Type is being disabled by an other transaction.

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  • log file not generated while accessing a jar having log4j support.

    - by naveen garimella
    I have a x.jar which is being used by some client y.jar. Both x.jar and y.jar are at the same package level. i have put the log4j.xml at the same package level. But the log file is never generated. Can i know why? I have tried few other options as well but no luck till now. i have added log4j-1.2.16.jar to ClassPath: variable in manifest files of both x.jar and y.jar. Put log4j.xml at the class level of y.jar which actually calls the x.jar classes. package structure is as follows: x.jar --manifest.mf has a entry ClassPath:log4j-1.2.16.jar y.jar --manifest.mf has a entry ClassPath:log4j-1.2.16.jar log4j-1.2.16.jar log4j.xml --has a RollingFileAppender. Can any one suggest whether i am missing anything?

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  • What is the common way to program action listeners?

    - by Roman
    I just started to learn how to use action listeners. To my understanding it works in the following way: There are some classes which contains "addActionListener" method by default (for example classes for buttons). Using this method we add an action listener to an object. For example: listenedObject.addActionListener(listeningObject). When an action with the "listenedObject" is performed, the "actionPerformed" method of the "listeningObject" will be called. So, it means that when we program a class for the listeningObject, we need to put there "actionPerformed" method. What is not clear to me, should we create a new class for every object that we want to listen. It does not seem to me as an elegant solution. On the other hand, if we have one action listener class for all (or at least many) object, than we have a problem since a instance of this class will not know which object is calling the "actionPerformed" method (and we need to know that since actions performed by the actionPerformed differs depending on who is called for this method). In my opinion, for every listened object we need to create are "personal" action listener and we can do it by setting a specific value to the corresponding field of the action listener. But I am not sure that it is a standard way to go? How do usually people do it?

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  • new Integer vs valueOf

    - by LB
    Hi, I was using Sonar to make my code cleaner, and it pointed that I'm using new Integer(1) instead of Integer.valueOf(1). Because it seems that valueOf does not instantiate a new object so is more memory-friendly. How can valueOf not instantiate a new object ? How does it work ? Is this true for all integers ? thanks.

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  • how can I enter character "<" in strings.xml?

    - by yrajabi
    I want to enter string " -< " in strings.xml file, the string has character < and I couldn't add it to xml file without error! I even tried to escaping by \ character: <string name="search_target_arrow"> -\< </string> or enclosing it between "" as below: <string name="search_target_arrow">" -< "</string> but none worked. Maybe I'm very amateur at this and the answer is not hard for you. so please tell me how you add such special chars in strings.xml?

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  • public (static) swap() method vs. redundant (non-static) private ones...

    - by Helper Method
    I'm revisiting data structures and algorithms to refresh my knowledge and from time to time I stumble across this problem: Often, several data structures do need to swap some elements on the underlying array. So I implement the swap() method in ADT1, ADT2 as a private non-static method. The good thing is, being a private method I don't need to check on the parameters, the bad thing is redundancy. But if I put the swap() method in a helper class as a public static method, I need to check the indices every time for validity, making the swap call very unefficient when many swaps are done. So what should I do? Neglect the performance degragation, or write small but redundant code?

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  • Manually manipulating ArrayList

    - by jsan
    I have an assignment where I have to create a deque, however I am not allowed to use any built-in classes or interfaces. I am implementing my deque using an array list. My problem is that when I have to, for instance, add to the beginning of the array list (beginning of the queue), i am not allowed to do this: public void addFirst(ArrayList<Integer> array) { array.add(0, int); } Is there a way to do this without using the add() function? Such as manually adding to the front and shifting the rest of the array to the right? Or maybe creating a new array list and copying...I'm not sure. Any help would be great; I have a bunch of functions to write, and getting the first one done will definitely put me in the right direction. Thanks

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  • How to remove strings of certain lengths

    - by Macosx Iam
    So I have this array, and I want to delete strings that are 2 or 4 characters in length (strings that contain 2 or 4 characters). I am doing this method, and it doesn't work, even though logically, it SHOULD work. public static void main(String[] args) { ArrayList<String> list = new ArrayList<String>(); list.add("This"); list.add("is"); list.add("a"); list.add("test"); for (int i=0; i<list.size(); i++) { if(list.get(i).length()==2 || list.get(i).length()==4) { list.remove(i); } } } I'd like to stick to this method of doing it. Can you please give me some suggestions as to how to correct this code? The output of this code when I run it is: [is, a] Even though I want the output to be [a] because "is" is 2 characters long.

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  • Join data from two Lists into one object

    - by Petr Mensik
    I ran into following situation and I am wondering about best solution. Let's say I have List<Object1> and List<Object2>, these lists are result of two separated queries. Both of them have the same size and there is relationship 1:1 between elements in the lists based on ID. I know that best solution would be fetching data in one DB query but that's possible right now. So my question is, what is the best way to join these lists into let's say List<Object3>?

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  • does anyone see any issues with this thread pattern?

    - by prmatta
    Here is a simple thread pattern that I use when writing a class that needs just one thread, and needs to a specific task. The usual requirements for such a class are that it should be startable, stopable and restartable. Does anyone see any issues with this pattern that I use? public class MyThread implements Runnable { private boolean _exit = false; private Thread _thread = null; public void start () { if (_thread == null) { _thread = new Thread(this, "MyThread"); _thread.start(); } } public void run () { while (_exit) { //do something } } public void stop () { _exit = true; if (_thread != null) { _thread.interrupt(); _thread = null; } } } I am looking for comments around if I am missing something, or if there is a better way to write this.

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  • Synchronize JTextFields Values by PropertyChangeListener

    - by gt_ebuddy
    I want to copy the value of a jTextField - TXTFLD1 to another jTextField -TXTFLD2 when the value at TXTFLD1 changes. I choose propertychangelistener because i cannot detect when the value at TXTFLD1 is changed, Because it is changed by some external code which i cannot modify now. The test code is as follows : public class TxtFldSync extends JFrame { private JButton BTN1 = null; private JTextField TXTFLD1 = null; private JTextField TXTFLD2 = null; public static void main(String[] args) { TxtFldSync thisClass = new TxtFldSync(); thisClass.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); thisClass.setVisible(true); } public TxtFldSync() { super(); this.setSize(300, 200); BTN1 = new JButton(); BTN1.setBounds(new Rectangle(178, 38, 67, 17)); TXTFLD1 = new JTextField(); TXTFLD1.setBounds(new Rectangle(32, 42, 83, 20)); TXTFLD2 = new JTextField(); TXTFLD2.setBounds(new Rectangle(30, 78, 83, 20)); //listeners TXTFLD1.addPropertyChangeListener("value", new PropertyChangeListener() { @Override public void propertyChange(PropertyChangeEvent arg0) { TXTFLD2.setText(TXTFLD1.getText()+"set by change listener"); //this doesnot work why ? } }); BTN1.addActionListener( new ActionListener() { @Override public void actionPerformed(ActionEvent arg0) { TXTFLD1.setText("Action Performed"); //i what to set same value to TXTFLD2 using property change listener } }); this.setContentPane(new Container()); this.getContentPane().add(BTN1); this.getContentPane().add(TXTFLD1); this.getContentPane().add(TXTFLD2); } } Why the property change listener is not working. What are the other alternatives solution for this problem?

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  • Refactoring a nested loop

    - by user3517441
    I have the following code which I use a lot of times in the class. for (int i = 0; i < someList.size(); i++) { for (int j = 0; j < someList.size(); j++) { if (i != j) { someList.get(i).sendMessageTo(someList.get(j))); //variable action } } } The purpose of the loop is to make each element in the List to send a message (or perform another action) to every element in the list except itself. Is there any way I can create a helper method so I don't have to repeat the loop code. I want to be able to state the variable action and call the helper method. Thanks.

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  • Can I have a set containing identical elements?

    - by Roman
    It is convenient for me to use a set. I like how I can "add" ("remove") an element to (from) the set. It is also convenient to check if a given element is in the set. The only problem, I found out that I cannot add a new element to a set if the set has already such an element. Is it possible to have "sets" which can contain several identical elements.

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  • Can I get the full query that a PreparedStatement is about to execute?

    - by ufk
    I'm working with PreparedStatement with MySQL server. example: String myQuery = "select id from user where name = ?"; PreparedStatement stmt = sqlConnection.prepareStatement(myQuery); stmt.setString(1, "test"); stmt.executeQUery(); ResultSet rs = stmt.getResultSet(); How can I receive the full SQL query that is about to be executed on the MySQL server? thanks!

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