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  • java casting confusion

    - by Stardust
    Could anyone please tell me why the following casting is resulting in compile time error: Long l = (Long)Math.pow(5,2); But why not the following: long l = (long)Math.pow(5,2);

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  • Cloning java ArrayList and preventing it from modifications

    - by user222164
    I have a data structure like a database Rowset, which has got Rows and Rows have Columns. I need to initialize a Columns with null values, current code is to loop thru each column for a row and initialize values to NULL. Which is very inefficient if you have 100s or rows and 10s of column. So instead I am keeping a initialized ArrayList of columns are RowSet level, and then doing a clone of this Arraylist for individual rows, as I believe clone() is faster than looping thru each element. row.columnsValues = rowsset.NullArrayList.clone() Problem with this is NullArrayList can be accidentally modified after being cloned, thus sacrificing the integrity of ArrayList at RowSet level, to prevent I am doing 3 things 1) Delcaring ArrayList as final 2) Any elements I insert are final or null 3) Methods thurough this arrayList are passed to other arrays are declared a final. Sounds like a plan, do you see any holes ?

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  • How to wrap Java String.format()?

    - by BlinK_
    Hey everyone, I would like to wrap the String.format() method with in my own Logger class. I can't figure a way how to pass arguments from my method to String.format(). public class Logger { public static void format(String format, Object... args) { print(String.format(format, args)); // <-- this gives an error obviously. } public static void print(String s) { System.out.println(s); } }

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  • Java Collections Sort not accepting comparator constructor with arg

    - by harmzl
    I'm getting a compiler error for this line: Collections.sort(terms, new QuerySorter_TFmaxIDF(myInteger)); My customized Comparator is pretty basic; here's the signature and constructor: public class QuerySorter_TFmaxIDF implements Comparator<Term>{ private int numberOfDocs; QuerySorter_TFmaxIDF(int n){ super(); numberOfDocs = n; } } Is there an error because I'm passing an argument into the Comparator? I need to pass an argument...

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  • How to serialize Java primitives using Jersey REST

    - by Olvagor
    In my application I use Jersey REST to serialize complex objects. This works quite fine. But there are a few method which simply return an int or boolean. Jersey can't handle primitive types (to my knowledge), probably because they're no annotated and Jersey has no default annotation for them. I worked around that by creating complex types like a RestBoolean or RestInteger, which simply hold an int or boolean value and have the appropriate annotations. Isn't there an easier way than writing these container objects?

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  • What is the best way to transmit Java objects over a network

    - by tomdee
    I am trying to transmit objects of a particular class from one server to another. The options I'm looking at are: Serialize the data as JSON and send it over the wire using HTTP, and de-serialize at the other end. Serialize the data into some binary form and transmit using TCP sockets. What are the best practices in this area? What are the gotchas? Ideally I would like the interface to be versioned, so the sender and receiver can be upgraded independently. I'm considering the JSON approach as I already have code that will serialize/deserialize the objects into JSON.

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  • Static variables in Java for a test oObject creator

    - by stevebot
    Hey, I have something like the following TestObjectCreator{ private static Person person; private static Company company; static { person = new Person() person.setName("Joe"); company = new Company(); company.setName("Apple"); } public Person createTestPerson(){ return person; } public Person createTestCompany(){ return company; } } By applying static{} what am I gaining? I assume the objects are singletons as a result. However, if I did the following: Person person = TestObjectCreator.createTestPerson(); person.setName("Jill"); Person person2 = TestObjectCreator.createTestPerson(); would person2 be named Jill or Joe?

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  • Write wave files to memory in Java

    - by Cliff
    I'm trying to figure out why my servlet code creates wave files with improper headers. I use: AudioSystem.write( new AudioInputStream( new ByteArrayInputStream(memoryBytes), new AudioFormat(22000, 16, 1, true,false), memoryBytes.length ), AudioFileFormat.Type.WAVE, servletOutputStream ); taking a byte array from memory containing raw PCM samples and a servlet output stream that gets returned to the client. In the result I get a normal wave file but with zeros in the chunk size fields. Is the API broken? I would think that the size could be filled in using the size passed in the audio input stream. But now, after typing this out I'm thinking its not making this info available to the outer write() method on AudioSystem. It seems like the AudioSystem.write call needs a size parameter unless it is able to pull the size from the stream... which wouldn't work with an arbitrary sized stream. Does anyone know how to make this example work?

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  • java serialization and final fields

    - by mdma
    I have an class defining an immutable value type that I now need to serialize. The immutability comes from the final fields which are set in the constructor. I've tried serializing, and it works (surprisingly?) - but I've no idea how. Here's an example of the class public class MyValueType implements Serializable { private final int value; private transient int derivedValue; public MyValueType(int value) { this.value = value; this.derivedValue = derivedValue(value); } // getters etc... } Given that the class doesn't have a no arg constructor, how can it be instantiated and the final field set? (An aside - I noticed this class particularly because IDEA wasn't generating a "no serialVersionUID" inspection warning for this class, yet successfully generated warnings for other classes that I've just made serializable.)

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  • Adding look and feel into java application

    - by Samurai
    I am working with NetBeans 6.5 IDE and i have downloaded a look and feel jar file. I added that to NetBeans by palette manager but i don't know how to use it to my application using code. Anybody please tell me that how to add look and feel into my application? Thanks..

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  • Mixed alignment with Java Swing's GroupLayout

    - by zigdon
    I'm trying to build a GUI window in my application. What I'm trying to do is have a window, with a few buttons at the top, and a large text area. Something like this: +--------------------------------------------------+ | [button1] [button2] [button3] | | +----------------------------------------------+ | | | text area | | | | | | | | | | | | | | | +----------------------------------------------+ | +--------------------------------------------------+ I'm almost there, using GroupLayout: layout.setHorizontalGroup( layout.createParallelGroup() .addGroup(layout.createSequentialGroup() .addComponent(button1) .addComponent(button2)) .addComponent(closeWindow)) .addComponent(textarea1) ); layout.setVerticalGroup( layout.createSequentialGroup() .addGroup(layout.createParallelGroup() .addComponent(button1) .addComponent(button2) .addComponent(button3)) .addComponent(textarea) ); The problem is that this ends up with button3 aligned to the left, with the other two. I can't seem to figure out how I can specify the alignment on just that one button. I can do GroupLayout.Alignment.TRAILING on the entire button bar, but that hits all 3 buttons, which is also not quite right. So what's the correct approach? Since the alignment only applies for Parallel Groups, I don't think having a HorizontalGroup with two Sequential Groups in it will help? What am I missing?

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  • Implementing Java Priority Queue

    - by Kay
    public class PriorityQueue<T> { private PriorityNode<T> head, tail; private int numItems; public PriorityQueue(){ numItems = 0; head=null; tail=null; } public void add(int priority, T value){ PriorityNode<T> newNode = new PriorityNode<T>(priority,value); if(numItems == 0){ head = newNode; tail = newNode; } else{ head.setNext(newNode); head = newNode; } } } Where PriorityNode is defined as: public class PriorityNode<T> implements Comparable<T> { private T value; private PriorityNode<T> next; private int priority; public PriorityNode(int priority,T newValue){ value = newValue; next = null; priority = 0; } public PriorityNode(T newValue){ value = newValue; next = null; priority = 0; } public void setPriority(int priority){ this.priority = priority; } public int getPriority(){ return this.priority; } public T getValue(){ return value; } public PriorityNode<T> getNext(){ return next; } public void setNext(PriorityNode<T> nextNode){ this.next = nextNode; } public void setValue(T newValue){ value = newValue; } public int compareTo(int pri) { // TODO Auto-generated method stub if(this.priority<pri){ return -1; } else if(this.priority == pri){ return 0; } else{ return 1; } } } I'm having a lot of difficulty using the Comparator here and implementing a priority queue - please point me in the right direction.

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  • Java - getConstructor() ?

    - by msr
    Hello, I wrote the question as a comment in the code, I think its easier to understand this way. public class Xpto{ protected AbstractClass x; public void foo(){ // AbstractClass y = new ????? Car or Person ????? /* here I need a new object of this.x's type (which could be Car or Person) I know that with x.getClass() I get the x's Class (which will be Car or Person), however Im wondering how can I get and USE it's contructor */ // ... more operations (which depend on y's type) } } public abstract class AbstractClass { } public class Car extends AbstractClass{ } public class Person extends AbstractClass{ }

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  • Java : HTTP POST Request

    - by SpunkerBaba
    I have to do a http post request to a web-service for authenticating the user with username and password. The Web-service guy gave me following information to construct HTTP Post request. POST /login/dologin HTTP/1.1 Host: webservice.companyname.com Content-Type: application/x-www-form-urlencoded Content-Length: 48 id=username&num=password&remember=on&output=xml The XML Response that i will be getting is <?xml version="1.0" encoding="ISO-8859-1"?> <login> <message><![CDATA[]]></message> <status><![CDATA[true]]></status> <Rlo><![CDATA[Username]]></Rlo> <Rsc><![CDATA[9L99PK1KGKSkfMbcsxvkF0S0UoldJ0SU]]></Rsc> <Rm><![CDATA[b59031b85bb127661105765722cd3531==AO1YjN5QDM5ITM]]></Rm> <Rl><![CDATA[[email protected]]]></Rl> <uid><![CDATA[3539145]]></uid> <Rmu><![CDATA[f8e8917f7964d4cc7c4c4226f060e3ea]]></Rmu> </login> This is what i am doing HttpPost postRequest = new HttpPost(urlString); How do i construct the rest of the parameters?

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  • Object Literals In Java?

    - by jjacquay712
    I am learning GWT for web development and came across a piece of code I can't really understand. helloBtn.addClickHandler(new ClickHandler() { public void onClick(ClickEvent event) { Window.alert("Hello!"); } }); If someone could explain to me what it is doing that would be great. Thanks, John

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  • Simple way to repeat a String in java

    - by e5
    I'm looking for a simple commons method or operator that allows me to repeat some String n times. I know I could write this using a for loop, but I wish to avoid for loops whenever necessary and a simple direct method should exist somewhere. String str = "abc"; String repeated = str.repeat(3); repeated.equals("abcabcabc"); Related to: repeat string javascript Create NSString by repeating another string a given number of times Edited I try to avoid for loops when they are not completely necessary because: They add to the number of lines of code even if they are tucked away in another function. Someone reading my code has to figure out what I am doing in that for loop. Even if it is commented and has meaningful variables names, they still have to make sure it is not doing anything "clever". Programmers love to put clever things in for loops, even if I write it to "only do what it is intended to do", that does not preclude someone coming along and adding some additional clever "fix". They are very often easy to get wrong. For loops that involving indexes tend to generate off by one bugs. For loops often reuse the same variables, increasing the chance of really hard to find scoping bugs. For loops increase the number of places a bug hunter has to look.

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  • Java: Print and access List <String[]>

    - by battousai622
    Im reading in a file and storing it in t1. How do i access the elements in t1? When i try to print it i get addresses instead of values. Also whats the dif between string and string[]? CSVReader reader = new CSVReader(new FileReader("src/new_acquisitions.csv")); List <String[]> t1 = reader.readAll(); int i = 0 while(i < t1.size()) { System.out.println(t1.get(i)); i++; } output: [Ljava.lang.String;@9304b1 [Ljava.lang.String;@190d11 [Ljava.lang.String;@a90653 [Ljava.lang.String;@de6ced

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  • java source code doubt

    - by abson
    this compiles class ex1 { public int show() { try { int a=10/10; return 10;} catch(ArithmeticException e) { System.out.println(e); } finally { System.out.println("Finally");} System.out.println("hello"); return 20; } } on the other hand this doesn't class ex15 { public int show() { try { int a=10/0; return 10;} catch(ArithmeticException e) { System.out.println(e); } finally { System.out.println("Finally"); return 40;} System.out.println("hello"); return 20; } } why is it so?

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  • Java: why can't iterate over an iterator?

    - by noamtm
    I read http://stackoverflow.com/questions/839178/why-is-javas-iterator-not-an-iterable and http://stackoverflow.com/questions/27240/why-arent-enumerations-iterable, but I still don't understand why this: void foo(Iterator<X> it) { for (X x : it) { bar(x); baz(x); } } was not made possible. In other words, unless I'm missing something, the above could have been nice and valid syntactic sugar for: void foo(Iterator<X> it) { for (X x; it.hasNext();) { x = it.next(); bar(x); baz(x); } }

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