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  • Java: Comparing a class with another within that class using a my own .equals

    - by user1670252
    I am making a method .equals replacing the equals method used. It accepts a object. I want it to check if that object equals the class that runs the .equals class. I know I want to compare all the private methods I have to that object. Is there a way to do this without making another private class to get the private variables from the object? How do I do this to compare equality not identity? I am stuck on this. Do i have to use == to compare? Also looking online i see others use recursion. If this is the way i have to do it can you show and explain it to me? so an example i have public boolean equals(Object o) { this is in a class we will call bobtheBuilder (first thing to pop in my head) I want to check if the object o is equal to the class he has private object array and a private int. I assume I want to check if the array and int of this class equal the array and int of the object.

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  • Avoiding duplicate objects in Java deserialization

    - by YGL
    I have two lists (list1 and list2) containing references to some objects, where some of the list entries may point to the same object. Then, for various reasons, I am serializing these lists to two separate files. Finally, when I deserialize the lists, I would like to ensure that I am not re-creating more objects than needed. In other words, it should still be possible for some entry of List1 to point to the same object as some entry in List2. MyObject obj = new MyObject(); List<MyObject> list1 = new ArrayList<MyObject>(); List<MyObject> list2 = new ArrayList<MyObject>(); list1.add(obj); list2.add(obj); // serialize to file1.ser ObjectOutputStream oos = new ObjectOutputStream(...); oos.writeObject(list1); oos.close(); // serialize to file2.ser oos = new ObjectOutputStream(...); oos.writeObject(list2); oos.close(); I think that sections 3.4 and A.2 of the spec say that deserialization strictly results in the creation of new objects, but I'm not sure. If so, some possible solutions might involve: Implementing equals() and hashCode() and checking references manually. Creating a "container class" to hold everything and then serializing the container class. Is there an easy way to ensure that objects are not duplicated upon deserialization? Thanks.

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  • Java, Massive message processing with queue manager (trading)

    - by Ronny
    Hello, I would like to design a simple application (without j2ee and jms) that can process massive amount of messages (like in trading systems) I have created a service that can receive messages and place them in a queue to so that the system won't stuck when overloaded. Then I created a service (QueueService) that wraps the queue and has a pop method that pops out a message from the queue and if there is no messages returns null, this method is marked as "synchronized" for the next step. I have created a class that knows how process the message (MessageHandler) and another class that can "listen" for messages in a new thread (MessageListener). The thread has a "while(true)" and all the time tries to pop a message. If a message was returned, the thread calls the MessageHandler class and when it's done, he will ask for another message. Now, I have configured the application to open 10 MessageListener to allow multi message processing. I have now 10 threads that all time are in a loop. Is that a good design?? Can anyone reference me to some books or sites how to handle such scenario?? Thanks, Ronny

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  • Internal Java code best practice for dealing with invalid REST API parameters

    - by user326389
    My colleague wrote the following stackoverflow question: other stack overflow question on this topic The question seems to have been misinterpreted and I want to find out the answer, so I'm starting this new question... hopefully a little more clear. Basically, we have a REST API. Users of our API call our methods with parameters. But sometimes users call them with the wrong parameters!! Maybe a mistake in their code, maybe they're just trying to play with us, maybe they're trying to see how we respond, who knows! We respond with HTTP status error codes and maybe a detailed description of the invalid parameter in the XML response. All is well. But internally we deal with these invalid parameters by throwing exceptions. For example, if someone looks up a Person object by giving us their profile id, but the profile id doesn't exist... we throw a PersonInvalidException when looking them up. Then we catch this exception in our API controller and send back an HTTP 400 status error code. Our question is... is this the best practice, throwing exceptions internally for this kind of user error? These exceptions never get propogated back to the user, this is a REST API. They only make our code cleaner. Otherwise we could have a validation method in each of our API controllers to make sure the parameters all make sense, but that seems inefficient. We have to look up things in our database potentially twice. Or we could return nulls and check for them, but that sucks... What are your thoughts?

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  • Java generics question with wildcards

    - by Sean
    Just came across a place where I'd like to use generics and I'm not sure how to make it work the way I want. I have a method in my data layer that does a query and returns a list of objects. Here's the signature. public List getList(Class cls, Map query) This is what I'd like the calling code to look like. List<Whatever> list = getList(WhateverImpl.class, query); I'd like to make it so that I don't have to cast this to a List coming out, which leads me to this. public <T> List<T> getList(Class<T> cls, Map query) But now I have the problem that what I get out is always the concrete List<WhateverImpl> passed in whereas I'd like it to be the Whatever interface. I tried to use the super keyword but couldn't figure it out. Any generics gurus out there know how this can be done?

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  • PLEASE HELP JAVA/SQL question

    - by fred-ghosn
    Hello everyone, well I'm new here and I really need some help.. I want to create a table and this table's name will be inserted from a textfield. However when I run the query it's giving me an error, any help on this one? Ill paste the code here: public boolean CreateTable() { TableNumber=jTextField4.getText(); try { String password = null; String s = "CREATE TABLE '"+TableNumber+'" (Item char(50),Price char(50))"; ConnectionForOrders(); stmt = conn.createStatement(); stmt.executeUpdate(s); boolean f=false; ConnectionForOrdersclose();

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  • Please clarify a few points concerning Java Servlets

    - by EugeneP
    suppose, I use Tomcat as a web container. Is it true that once all the servlets found in a web-app/WEBAPPNAME are init(IALIZED) then every change of a Servlet's property will be seen to every session. So session 1 changes a property userName of a Servlet1 from "user1" to "user2" session 1 is closed. session 2 starts. It will see "user2" as the only value of Servlet1.userName property?? Any change of a Servlet's field will be seen to all subsequent sessions? Are servlets singletons, aren't they?

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  • Java: Convenient way to refactor the application.

    - by Harshal
    Hi, Everyone We have an agile enterprise application built on JSP and Servlet without any design strategy. This application was built in early 2002 considering 1000 users. After 2002, we received lots of requests from the marketing partners. Currently, the application has lots of spaghetti code with lots of Ifs and elses. One class has more than 20,000 lines of code with a huge body of functions without abstraction. Now, we need to support billions of records, what we need to do immediately and gradually? We have to refactor the application? Which framework, we need to use? How the usage of the framework will be helpful to the end users? How to convince the leaders to do the refactoring? How to gain the faster response time as compare to the current system?

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  • Getter/Setter (composition, Java, HW)

    - by Crystal
    I have one class called Person that basically looks like: public class Person { String firstName; String lastName; String telephone; String email; public Person() { firstName = ""; lastName = ""; telephone = ""; email = ""; } public Person(String firstName, String lastName, String telephone, String email) { this.firstName = firstName; this.lastName = lastName; this.telephone = telephone; this.email = email; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } .... Using that class, I setup an abstract class called Loan that looks like: public abstract class Loan { public void setClient(Person client) { this.client = client; } public Person getClient() { return client; } public void setLoanId(int nextId) { loanId = nextId; nextId++; } public int getLoanId() { return loanId; } public void setInterestRate(double interestRate) { this.interestRate = interestRate; } public double getInterestRate() { return interestRate; } public void setLoanLength(int loanLength) { this.loanLength = loanLength; } public int getLoanLength() { return loanLength; } public void setLoanAmount(double loanAmount) { this.loanAmount = loanAmount; } public double getLoanAmount(double loanAmount) { return loanAmount; } private Person client; private int loanId; private double interestRate; private int loanLength; private double loanAmount; private static int nextId = 1; } I have to extend the Loan class with CarLoan and it looks like: public class CarLoan extends Loan { public CarLoan(Person client, double vehiclePrice, double downPayment, double salesTax, double interestRate, CAR_LOAN_TERMS length) { super.setClient(client); super.setInterestRate(interestRate); this.client = client; this.vehiclePrice = vehiclePrice; this.downPayment = downPayment; this.salesTax = salesTax; this.length = length; } public void setVehiclePrice(double vehiclePrice) { this.vehiclePrice = vehiclePrice; } public double getVehiclePrice() { return vehiclePrice; } public void setDownPayment(double downPayment) { this.downPayment = downPayment; } public double getDownPayment() { return downPayment; } public void setSalesTax(double salesTax) { this.salesTax = salesTax; } public double getSalesTax() { return salesTax; } public String toString() { return getClass().getName() + "[vehiclePrice = " + vehiclePrice + '\n' + "downPayment = " + downPayment + '\n' + "salesTax = " + salesTax + "]"; } public enum CAR_LOAN_TERMS {TWO_YEAR, THREE_YEAR, SIX_YEAR}; private double vehiclePrice; private double downPayment; private double salesTax; Few questions. (a) Is what I did in the Loan class to setClient correct given what I have in the Person class? (e.g.this.client = client) (b) Can I call super twice in a method? I have to set two attributes from the Loan class from the constructor in the CarLoan class and I thought that would be a way to do it. (c) Do you have to set attributes for enumeration types differently in a constructor or getter/setter methods? I get an error for (this.length = length) in my CarLoan class and I was unsure of how enumeration values should be set. Thanks!

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  • Java Swing - Adding a row # column (row header) to a JTable

    - by llm
    I have data from a database loaded into a JTable through a custom table model. I want to have a column (should be the first column) which simply shows the display row number (i.e. it is not tied to any data (or sorting) but is simply the row number on the screen starting at 1). These "row headers" should be grayed out like the row headers. Any idea how to do this? Thanks

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  • Java file searching problem

    - by Infinity
    Hello guys! I need to search a file for a word and return the whole line and the line number with this word, then edit the line and write back to the file. Maybe the line number isn't necesary to edit a line in a file. I `was reading after seraching with regexp and opening the filechannel of the file, but I can't get the line number. Maybe there are other better ways to do this. Can you help me how to start this?

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  • creating Sites using java

    - by rajalakshmi
    Hi i developed one application used to create google sites by referring the developer guide in which i don't know what are the three parameters in this is particular line SitesService client = new SitesService("yourCo-yourAppName-v1"). This is my problem. help me

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  • Generate a collection of changed lines between two revisions of a file using Java

    - by mchr
    I am writing an eclipse plugin which needs to be able to determine which lines of a file have changed compared to a different version of the same file. Is there an existing class or library which I can use for this task? The closest I have found is org.eclipse.compare.internal.merge.DocumentMerger. This can be used to find the information I need but is in an internal package so is not suitable for me to use. I could copy/paste the source of this class and adapt it to my requirements. However, I am hoping there is an existing library to handle textual comparisons.

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  • Java : Singleton class instances in a Web based Application

    - by Preethi Jain
    I have this Singleton class inside a Web Application . public class MyDAO { private static MyDAO instance; private MyDAO() { } public static MyDAO getInstance() { if (instance == null) { instance = new MyDAO(); } return instance; } I will access it this way public void get_Data() { MyDAO dao = MyDAO.getInstance(); } How many Objects of MyDAO class will be created if there are 3 Users accessing the Application ?? Will there be one instance of MyDAO per User ??

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  • Java Timer not working

    - by Jacob
    I have an Image named worldImageToUse and I have a Timer that is supposed to toggle worldImageToUse between two images every 1 second. But it does not seem to work. Help Please? public void startWorldImageFlash() { worldImageFlashTimer = new Timer(); TimerTask task = new TimerTask() { @Override public void run() { if(worldImageToUse == worldImage) setWorldImageBW(); if(worldImageToUse == worldImageBW) setWorldImageColor(); } }; worldImageFlashTimer.scheduleAtFixedRate(task, 0, 1000); } public void stopWorldImageFlash() { worldImageFlashTimer.cancel(); setWorldImageColor(); }

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  • Removing whitespace in Java string?

    - by waitinforatrain
    Hi guys, I'm writing a parser for some LISP files. I'm trying to get rid of leading whitespace in a string. The string contents are along the lines of: :FUNCTION (LAMBDA (DELTA PLASMA-IN-0) (IF (OR (>= #61=(+ (* 1 DELTA) PLASMA-IN-0) 100) (<= #61# 0)) PLASMA-IN-0 #61#)) The tabs are all printed as 4 spaces in the file, so I want to get rid of these leading tabs. I tried to do this: string.replaceAll("\\s{4}", " ") - but it had no effect at all on the string. Does anyone know what I'm doing wrong? Is it because it is a multi-line string? Thanks

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  • Android / Java rare and seemingly impossible exception causing force close

    - by Guzba
    Hello all, I have an interesting problem being reported to me from an android application I have published. I have a two-dimensional array that I am iterating through using two for loops like so: for (int i = 0; i < arr.length; ++i) { for (int j = 0; j < arr[i].length; ++j) { if (arr[i][j] != 0) // does stuff } } The problem is, somehow arr[i][j] != 0 is throwing an ArrayIndexOutOfBoundsException. But very rarely. I have thousands of people use the app on a daily basis and get maybe twenty force close reports. Is this something I can't avoid, maybe a problem with the phones memory, etc. or is there something I can do that I haven't thought of yet? Thanks.

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  • Distinguish between a single click and a double click in Java

    - by user552279
    Hi, I search the forum and see this codes: public void mouseClicked(MouseEvent e) { if (e.getClickCount() == 2) { System.out.println(" and it's a double click!"); wasDoubleClick = true; } else { Integer timerinterval = (Integer) Toolkit.getDefaultToolkit().getDesktopProperty( "awt.multiClickInterval"); timer = new Timer(timerinterval.intValue(), new ActionListener() { public void actionPerformed(ActionEvent evt) { if (wasDoubleClick) { wasDoubleClick = false; // reset flag } else { System.out.println(" and it's a simple click!"); } } }); timer.setRepeats(false); timer.start(); } } but the code runs incorrectly(Sometime it prints out " and it's a single click!" 2 times . It should print out " and it's a double click!"). Can anybody show me why? or can you give me some better ways to do this? Thank you!

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  • Why are these lines being skipped? (java)

    - by David
    Here's the relevant bit of the source code: class Dice { String name ; int x ; int[] sum ; ... public Dice (String name) { this.name = name ; this.x = 0 ; this.sum = new int[7] ; } ... public static void main (String[] arg) { Dice a1 = new Dice ("a1") ; printValues (a1) ; } public static void printDice (Dice Dice) { System.out.println (Dice.name) ; System.out.println ("value: "+Dice.x) ; printValues (Dice) ; } public static void printValues (Dice Dice) { for (int i = 0; i<Dice.sum.length; i++) System.out.println ("#of "+i+"'s: "+Dice.sum[i]) ; } } Here is the output: #of 0's: 0 #of 1's: 0 #of 2's: 0 #of 3's: 0 #of 4's: 0 #of 5's: 0 #of 6's: 0 Why didn't these two lines execute inside printDice: System.out.println (Dice.name) ; System.out.println ("value: "+Dice.x) ; if they had then i would expect to see "a1" and "Value: 0" printed at the top of the rows of #of's

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  • Java: serial thread confinement question

    - by denis
    Assume you have a Collection(ConcurrentLinkedQueue) of Runnables with mutable state. Thread A iterates over the Collection and hands the Runnables to an ExecutorService. The run() method changes the Runnables state. The Runnable has no internal synchronization. The above is a repetitive action and the worker threads need to see the changes made by previous iterations. So a Runnable gets processed by one worker thread after another, but is never accessed by more than one thread at a time - a case of serial thread confinement(i hope ;)). The question: Will it work just with the internal synchronization of the ConcurrentLinkedQueue/ExecutorSerivce? To be more precise: If Thread A hands Runnable R to worker thread B and B changes the state of R, and then A hands R to worker thread C..does C see the modifications done by B?

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  • Java Logger only to file, no screen output!

    - by Tom Taylor
    Hello there SO'ers, I got a quite simple problem but cant find a solution for it. I have a logger with a file handler added, but it still spams to hell out of my console. How could I get the logger to solely route all output to a file, with NO console outputs? Thanks a lot, cru

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