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  • this and super in java

    - by abson
    this and super are keywords isn't it, then how can we use them for passing arguments to constructors the same way as with a method?? In short how is it that these can show such distinct behaviours??

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  • Java connecting to Http which method to use?

    - by jax
    I have been looking around at different ways to connect to URLs and there seem to be a few. My requirements are to do POST and GET queries on a URL and retrieve the result. I have seen URL class DefaultHttpClient class And there were some others in apache commons which method is best?

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  • Java - Does null variable require space in memory

    - by Yatendra Goel
    class CheckStore { private String displayText; private boolean state; private String meaningfulText; private URL url; public CheckStore(String text, boolean state) { this.displayText = text; this.state = state; } : : } As I am initializing only two variables (displayText and state) in the constructor, Will the rest two variables (meaningfulText and url which will have the value null) will require space in memory to store null value. Q1. I think they will require space. If they will, then how much memory does a null value takes in the memory (like int takes 4 bytes). Q2. How much space a string takes in memory. I guess it will depend on the length of the string. So how much space a string takes of how much length?

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  • Java ActionListener buttonPress() restriction

    - by Extinct23
    Is there a way to restrict this button to only being impressed once? The reason I ask is because for some reasons every time the button is pressed it disrupts the rest of my code. So in effort to save a massive amount of time debugging, it would be much easier to just somehow restrict the number of times it can be pressed. Thanks in advance. ActionListener pushButton = new buttonPress(); start.addActionListener(pushButton);

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  • Thread Code...anything wrong with this, must use java 1.4

    - by bmw0128
    I have a servlet automatically firing up when the app server starts, and in its init(), I'm making another thread: init(){ new FooThread() } in FooThread(), i want to periodically check the status of a DB value, then depending on the value, make a web service call. When these two tasks complete, I want the thread to sleep to wait a certain period then repeat. This cycle would just continue forever. FooThread: public class FooThread implements Runnable{ Thread t; FooThread(){ t = new Thread(this, "BBSThread"); logger.info("*** about to start " + t.getName()); t.start(); logger.info("*** started: " + t); } public void run() { try{ while(true){ //do the db check, then conditionally do the web services call logger.info("*** calling sleep() ***"); Thread.sleep(50000); logger.info("*** now awake ***"); } } catch (InterruptedException e) { System.out.println("*** FooThread interrupted"); } } }

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  • java.lang.classcastExcption

    - by Tara Singh
    Hi, I have an array list of objects in my application. private static ArrayList<Player> userList=new ArrayList<Player>(); In my application, I am converting this list to byte array and then sending it to other clients. At client When I am trying to cast it back to the ArrayList, its giving me casting error. I am doing this in client side after receiving this list as byte array: ArrayList<Player> pl = (ArrayList<Player>) toObject(receivedByteArray); where toObject is my function to convert the byte array to object; Any Suggestions please !!! Thanks.

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  • Exception and Inheritance in JAVA

    - by user1759950
    Suppose we have this problem public class Father{ public void method1(){...} } public class Child1 extends Father{ public void method1() throws Exception{ super.method1(); ... } } Child1 extends Father and override method1 but given implementation Child1.method1 now throws a exception, this wont compile as override method can't throw new exceptions. What is the best solution? Propagate the required exception to the Father.. to me this is against encapsulation, inheritance and general OOP ( the father potentially throw and exception that will never happen ) Use a RuntimeException instead? This solution wont propagate the Exception to the father but I read In Oracle docs and others sources states class of exceptions should be used when "Client code cannot do anything" this is not that case, this exception will b useful to recover blablabla ( why is wrong to use RuntimeException instead? ) Other.. thanks, Federico

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  • what databases can be used with java?

    - by aadersh patel
    I am doing an undergrad final project, and need to justify my choice of MySQL for the database element of my project. Truth is, it's the only one I can really use, and hence I went for it. What other database systems could I have used? Any advantages and disadvantages of these over MySQL?

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  • Reflection for Class of generic parameter in Java?

    - by hatboysam
    Imagine the following scenario: class MyClass extends OtherClass<String>{ String myName; //Whatever } class OtherClass<T> { T myfield; } And I am analyzing MyClass using reflection specifically (MyClass.class).getDeclaredFields(), in this case I will get the following fields (and Types, using getType() of the Field): myName --> String myField --> T I want to get the actual Type for T, which is known at runtime due to the explicit "String" in the extends notation, how do I go about getting the non-genetic type of myField?

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  • Can I add a java portlet to an existing java Web App?

    - by user323561
    Hi. I'm building a webapp that uses jboss-seam with jsf, facelets and rich faces, running on top of jboss AS 5.1. I would like to add a portlet area where I could add my own portlets, but from what I got (reading forums and documentation) I need to be running a portlet container/portal (something like liferay or gatein). But I don't want to be running a portal. I just want some kind of control where I can embed a portlet (something like an iFrame). Is this true or I got it wrong? If I'm wrong, how can I add an area to my webapp where I can add a portlet? Thanks Best regards.

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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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  • Java Matrix Transpose strangeness going on

    - by user1459976
    ok so im making my own Matrix class. and i have a transpose method that transposes a matrix. this is the block in the main method Matrix m1 = new Matrix(4,2); m1.fillMatrix(1,2,3,4,5,6,7,8); System.out.println("before " + m1.toString()); m1.transpose(); System.out.println("after " + m1.toString()); this is where it gets messed up, at m1.transpose(); in the transpose() method public Matrix transpose() { if(isMatrix2) { Matrix tempMatrix = new Matrix(row, col); // matrix2 contents are emptied once this line is executed for(int i=0; i < row; i++) { for(int j=0; j < col; j++) tempMatrix.matrix2[i][j] = matrix2[i][j]; } so for some reason, the tempMatrix.matrix2 has the same id as this.matrix2. so when the codes executes Matrix tempMatrix = new Matrix(row,col); then the contents of this.matrix2 is emptied. anyone know what might be going on here?

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  • Method-Object pairs in Java

    - by John Manak
    I'd like to create a list of method-object pairs. Each method is a function returning a boolean. Then: foreach(pair) { if method evaluates to true { do something with the object } } One way of modelling this that I can think of is to have a class Constraint with a method isValid() and for each constraint produce an anonymous class (overriding the isValid() method). I feel like there could be a nicer way. Can you think of any?

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  • best way to create UI java apps ?

    - by fwfwfw
    I've come across Netbeans but is there any tools out there that lets you build things event driven ? I'm looking for a feature like being able to drag and drop UI components, and add methods to buttons directly by double clicking it (kinda like visualbasic) and viewing the source.

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  • Relating text fields to check boxes in Java

    - by Finzz
    This program requires the user to login and request a database to access. The program then gets a connection object, searches through the database storing the column names into a vector for later use. The problem comes with implementing text fields to allow the user to search for specific values within the database. I can get the check boxes and text fields to appear using a gridlayout and add them to a panel. How do I relate the text fields to their appropriate check box? I've tried adding them to a vector, but then they can't also be added to the panel as well. I've searched for a way to name the text fields as the loop cycles through the column names, but it seems impossible to do without having them declared ahead of time. This can't be done either, as it's impossible to determine the attributes that the user will request. I just need to be able to know the names of the text fields so I can test to see if the user entered information and perform the necessary logic. Let me know if you have to see the rest of the code to give an answer, but hopefully you get the general idea of what I'm trying to accomplish. Picture of UI: try { ResultSet r2 = con.getMetaData().getColumns("", "", rb.getText(), ""); colNames1 = new Vector<String>(); columns1 = new Vector<JCheckBox>(); while (r2.next()) { colNames1.add(r2.getString(4)); JCheckBox cb = new JCheckBox(r2.getString(4)); JTextField tf = new JTextField(10); columns1.add(cb); p3.add(cb); p3.add(tf); } }

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  • Intercommunication between Java Chat Servers

    - by Pravingate
    I have a application in which I am using socket programming , having this(image) scenario. Where number of clients will try to connect Broadcast server. Now here I am managing load through LVS(Load balancer). so as a example shown in image, suppose 200 clients will wish to login for broadcast they will be distributed as 100 users on server 1 and another 100 users on server 2.clients will get connected to servers using TCP connection. Now I am maintaining user information on server side in arraylist which will be stored in heap memory,Now the problem is if client wish to broadcast to all logged in users, but that particular client is logged in server 1. and so client will not be able to broadcast another 100 users from server 2. Because both ther servers are unaware about each others state. please suggest to solve this scenario by whatever means you want.

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  • Java Object Array item to String Array

    - by user341264
    Say I have the following: Class myclass { public string stra ="", strb = "" myclass(String a, String b){stra=a;strb=b} } //then in the app I want to do: myclass myclassinst1 = new myclass("blah","xxxx"); myclass myclassinst2 = new myclass("blah2","yyyy"); myclass myclassinst3 = new myclass("blah3","zzzz"); list <myclass> mylist = new ArrayList<myclass>(); mylist.add(myclassinst1 ); mylist.add(myclassinst2 ); mylist.add(myclassinst3 ); //How would I then convert that to a String[] Array of all the stra elements without using a loop. //eg: String[] strarr_a = mylist.toarray(myclass.stra); String[] strarr_b = mylist.toarray(myclass.strb); //instead of having to do String[] strarr_a = new String[mylist.size()]; String[] strarr_b = new String[mylist.size()]; for (int i=0;i<mylist.size();i++) { strarr_a[i] = mylist.get(i).stra; strarr_b[i] = mylist.get(i).strb; }

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  • odd behavior with java collections of parameterized Class objects

    - by Paul
    Ran into some questionable behavior using lists of parameterized Class objects: ArrayList<Class<String>> classList = new ArrayList<Class<String>>(); classList.add(Integer.class); //compile error Class intClass = Integer.class; classList.add(intClass); //legal apparently, as long as intClass is not parameterized Found the same behavior for LinkedList, haven't tried other collections. Is it like this for a reason? Or have I stumbled on something?

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  • Negative look ahead java

    - by venu
    I need an expression to capture a string like this "A"[A string that is NOT atleast 5 and atmost 6 digits]"B", In other words capture anything that is NOT the following A[0-9][0-9][0-9][0-9][0-9]B A[0-9][0-9][0-9][0-9][0-9][0-9]B I have tried the negative look ahead regex = "a((?![0-9]{5,6}).)*d" ; But it fails to capture all scenarios. Please help venu

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  • java beginner- in which folder should I place a "database.properties" file

    - by Arvind
    I read some tutorials on how to read data from a database.properties file- which basically stored key-value pairs. What i want to know is, in which folder should I place this file? Is it in the root (ie "src") or within a package... And how do I access this file, if it is placed in "src"- my code will be within a package (and the package's directory will be under src)- so how do I access the properties file, which is in "src", from a class within a package?

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