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  • How does a Java Arraylist contains() method evalute objects?

    - by mvid
    Say i create one object and add it to my ArrayList. If I then create another object with exactly the same constructor input, will the contain() method evaluate the two objects to be the same? Assume the constructor doesn't do anything funny with the input, and the variables stored in both objects are identical. ArrayList<Thing> basket = new ArrayList<Thing>(); Thing thing = new Thing(100); basket.add(thing); Thing another = new Thing(100); basket.contains(another); // true or false?

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  • Java InputReader. Detect if file being read is binary?

    - by Trizicus
    I had posted a question in regards to this code. I found that JTextArea does not support the binary type data that is loaded. So my new question is how can I go about detecting the 'bad' file and canceling the file I/O and telling the user that they need to select a new file? class Open extends SwingWorker<Void, String> { File file; JTextArea jta; Open(File file, JTextArea jta) { this.file = file; this.jta = jta; } @Override protected Void doInBackground() throws Exception { BufferedReader br = null; try { br = new BufferedReader(new FileReader(file)); String line = br.readLine(); while(line != null) { publish(line); line = br.readLine(); } } finally { try { br.close(); } catch (IOException e) { } } return null; } @Override protected void process(List<String> chunks) { for(String s : chunks) jta.append(s + "\n"); } }

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  • Am I doing getters/setters the right way in Java?

    - by Sergio Tapia
    public class Persona { int Codigo; String Nombre; public Persona(int Codigo, String Nombre){ this.Codigo = Codigo; this.Nombre = Nombre; } public void setCodigo(int Codigo){ this.Codigo = Codigo; } public int getCodigo(){ return this.Codigo; } public void setNombre(String Nombre){ this.Nombre = Nombre; } public String getNombre(){ return this.Nombre; } } Or is there a much shorter (realiable) way to do it?

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  • Java: how to tell if a line in a text file was supposed to be blank?

    - by defn
    I'm working on a project in which I have to read in a Grammar file (breaking it up into my data structure), with the goal of being able to generate a random "DearJohnLetter". My problem is that when reading in the .txt file, I don't know how find out whether the file was supposed to be a completely blank line or not, which is detrimental to the program. Here is an example of part of the file, How do i tell if the next line was supposed to be a blank line? (btw I'm just using a buffered reader) Thanks! <start> I have to break up with you because <reason> . But let's still <disclaimer> . <reason> <dubious-excuse> <dubious-excuse> , and also because <reason> <dubious-excuse> my <person> doesn't like you I'm in love with <another> I haven't told you this before but <harsh> I didn't have the heart to tell you this when we were going out, but <harsh> you never <romantic-with-me> with me any more you don't <romantic> any more my <someone> said you were bad news

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  • How to create extensible dynamic array in Java without using pre-made classes?

    - by AndrejaKo
    Yeah, it's a homework question, so givemetehkodezplsthx! :) Anyway, here's what I need to do: I need to have a class which will have among its attributes array of objects of another class. The proper way to do this in my opinion would be to use something like LinkedList, Vector or similar. Unfortunately, last time I did that, I got fire and brimstone from my professor, because according to his belief I was using advanced stuff without understanding basics. Now next obvious solution would be to create array with fixed number of elements and add checks to get and set which will see if the array is full. If it is full, they'd create new bigger array, copy older array's data to the new array and return the new array to the caller. If it's mostly empty, they'd create new smaller array and move data from old array to new. To me this looks a bit stupid. For my homework, there probably won't be more that 3 elements in an array, but I'd like to make a scalable solution without manually calculating statistics about how often is array filled, what is the average number of new elements added, then using results of calculation to calculate number of elements in new array and so on. By the way, there is no need to remove elements from the middle of the array. Any tips?

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  • Problems importing WAR files in Eclipse?

    - by CitadelCSAlum
    I was unfortunately forced to result to uploading a WAR file as my backup for a web application I am working on. Luckily I have the most recent WAR file available. I am using Eclipse IDE and am using the Web Tools plugin for all the J2EE work that I am doing with the Dynamic Web Application Project. When I imported my WAR file, and ran it on a local server, everything works fine. The problem I a ran into is that in the Java Resources/src folder that all my packages and .java files were now only consists of all the same packages, but they are empty. I checked to see if I could find the files and I found the .class files in an "Imported files" folder that is not accessible in the Eclipse Project Explorer. I believe that I need to do some type of build or something so that my .java files are available for me, but unfortunately this is one area where I lack. One thing I would also like to know is, one way or the other, am I able to obtain the .java source code files if I have access to the .class files? Also, I would like to configure this environment as it was before where my Java Resources:src folder contaiend the packages and .java files.

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  • Java: Sharing a connection pool accross other J2SE Apps...?

    - by Zombies
    So I have a connection pool setup. Which is great and all since I have an application that really needs it. However what I would like to know is if it is possible to share this connection pool with other J2SE apps? Would this even be worth it, as opposed to creating a connection pool based on each apps needs? If it would be prudent, how can I accomplish this?

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  • How to authenticate my own provider( only for testing purposes)

    - by user308806
    Dear all Now, I wrote a new provider (ESMJCE provider), and I also write a simple application to test it, but I have some exceptions like that java.lang.SecurityException: JCE cannot authenticate the provider ESMJCE at javax.crypto.Cipher.getInstance(DashoA13*..) at javax.crypto.Cipher.getInstance(DashoA13*..) at testprovider.main(testprovider.java:27) Caused by: java.util.jar.JarException: Cannot parse file:/C:/Program%20Files/Java/jre1.6.0_02/lib/ext/abc.jar at javax.crypto.SunJCE_c.a(DashoA13*..) at javax.crypto.SunJCE_b.b(DashoA13*..) at javax.crypto.SunJCE_b.a(DashoA13*..) ... 3 more And here is my source code import java.security.Provider; import java.security.Security; import javax.crypto.Cipher; import esm.jce.provider.ESMProvider; public class testprovider { / @param args / public static void main(String[] args) { // TODO Auto-generated method stub ESMProvider esmprovider = new esm.jce.provider.ESMProvider(); Security.insertProviderAt(esmprovider,2); Provider[] temp = Security.getProviders(); for (int i= 0; i<temp.length; i++){ System.out.println("Providers: " temp[i].getName()); } try{ Cipher cipher = Cipher.getInstance("DES", "ESMJCE"); System.out.println("Cipher: " cipher); int blockSize= cipher.getBlockSize(); System.out.println("blockSize= " + blockSize); }catch (Exception e){ e.printStackTrace(); } } } Please help me solve this issue Thanks

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  • Java Swing: How to make the JComboxBox drop down list taller?

    - by NoozNooz42
    How to make the "dropdown" (or "popup", I don't know how it's called) of a JComboBox taller on the screen? By default, when I open my JComboBox I see, say, 7 out of 29 items, then I need to scroll. What should I do so that I can see, say, 15 out of these 32 items? (or if the dropdown is, say, 150 pixels tall, how can I make it 300 pixels tall?) I've read the Sun tutorial on JComboBox and the JavaDoc but I must have overlooked the method(s) to call.

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  • Java multi-threading - what is the best way to monitor the activity of a number of threads?

    - by MalcomTucker
    I have a number of threads that are performing a long runing task. These threads themselves have child threads that do further subdivisions of work. What is the best way for me to track the following: How many total threads my process has created What the state of each thread currently is What part of my process each thread has currently got to I want to do it in as efficient a way as possible and once threads finish, I don't want any references to them hanging around becasuse I need to be freeing up memory as early as possible. Any advice?

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  • Java encryption : with method can get me a shorter message ?

    - by Frank
    I don't know too much about encryption, I just want to ask, which method can get me the shortest result message ? For instance, the message looks like this : "This is the secret input message", I wonder if the encrypted message can be shorter then the above 32 characters long ? Maybe something like "dfkfjkvf12". Frank

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  • Read from one large file and write to many (tens, hundreds, or thousands) files in Java?

    - by Rudiger
    I have a large-ish file (4-5 GB compressed) of small messages that I wish to parse into approximately 6,000 files by message type. Messages are small; anywhere from 5 to 50 bytes depending on the type. Each message starts with a fixed-size type field (a 6-byte key). If I read a message of type '000001', I want to write append its payload to 000001.dat, etc. The input file contains a mixture of messages; I want N homogeneous output files, where each output file contains only the messages of a given type. What's an efficient a fast way of writing these messages to so many individual files? I'd like to use as much memory and processing power to get it done as fast as possible. I can write compressed or uncompressed files to the disk. I'm thinking of using a hashmap with a message type key and an outputstream value, but I'm sure there's a better way to do it. Thanks!

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  • Why does using Collections.emptySet() with generics work in assignment but not as a method parameter

    - by Karl von L
    So, I have a class with a constructor like this: public FilterList(Set<Integer> labels) { ... } and I want to construct a new FilterList object with an empty set. Following Joshua Bloch's advice in his book Effective Java, I don't want to create a new object for the empty set; I'll just use Collections.emptySet() instead: FilterList emptyList = new FilterList(Collections.emptySet()); This gives me an error, complaining that java.util.Set<java.lang.Object> is not a java.util.Set<java.lang.Integer>. OK, how about this: FilterList emptyList = new FilterList((Set<Integer>)Collections.emptySet()); This also gives me an error! Ok, how about this: Set<Integer> empty = Collections.emptySet(); FilterList emptyList = new FilterList(empty); Hey, it works! But why? After all, Java doesn't have type inference, which is why you get an unchecked conversion warning if you do Set<Integer> foo = new TreeSet() instead of Set<Integer> foo = new TreeSet<Integer>(). But Set<Integer> empty = Collections.emptySet(); works without even a warning. Why is that?

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