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  • Java: how to have global values inside a class?

    - by HH
    I want less methods. I want a common global TestClass from which I could use any of its value inside the class. import java.util.*; import java.io.*; public class TestClass { TestClass(String hello){ String hallo = hello; String halloSecond = "Saluto!"; } public static void main(String[] args) { TestClass test = new TestClass("Tjena!"); System.out.println("I want "Tjena!": " + test.hallo); TestClass testSecond = new TestClass("1"); System.out.println("I want Saluto!:" + test.halloSecond); System.out.println("I want Saluto!:" + testSecond.halloSecond); // How can I get glob.vars like the "Saluto!"? } }

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  • [java] how to use XML sent by html form?

    - by user32167
    i have html form with textarea in which i paste some XML, for example: <network ip_addr="10.0.0.0/8" save_ip="true"> <subnet interf_used="200" name="lan1" /> <subnet interf_used="254" name="lan2" /> </network> When user submit form, that data is send to Java server, so in headers i get something like that: GET /?we=%3Cnetwork+ip_addr%3D%2210.0.0.0%2F8%22+save_ip%3D%22true%22%3E%0D%0A%3Csubnet+interf_used%3D%22200%22+name%3D%22lan1%22+%2F%3E%0D%0A%3Csubnet+interf_used%3D%22254%22+name%3D%22lan2%22+%2F%3E%0D%0A%3C%2Fnetwork%3E HTTP/1.1 how can i use that in my Java applications? I need to make some calculations on that data and re-send new generated XML.

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  • Java equivalent for database schema changes like South for Django?

    - by gerdemb
    I've been working on a Django project using South to track and manage database schema changes. I'm starting a new Java project using Google Web Toolkit and wonder if there is an equivalent tool. For those who don't know, here's what South does: Automatically recognize changes to my Python database models (add/delete columns, tables etc.) Automatically create SQL statements to apply those changes to my database Track the applied schema migrations and apply them in order Allow data migrations using Python code. For example, splitting a name field into a first-name and last-name field using the Python split() function I haven't decided on my Java ORM yet, but Hibernate looks like the most popular. For me, the ability to easily make database schema changes will be an important factor.

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  • Why's a simple change to rt.jar causing the Java Runtime Environment to crash silently?

    - by Tom
    This is what I'm doing: extract contents of my JRE's rt.jar extract src.zip of my JDK (same version) Now, if I copy Runtime.java from the extracted src folder and compile it using javac.exe without any modifications and then put it in the extracted rt folder to finally put everything back in a jar file using jar.exe, everything works as expected. The JRE runs fine. However, if I make the slightest change to Runtime.java and compile it and put it in rt.jar, the JRE crashes whenever I attempt to start it. This is an example of a slight change that causes the silent crash: /** Don't let anyone else instantiate this class */ private Runtime() { System.out.println("This is a test."); } Instead of: /** Don't let anyone else instantiate this class */ private Runtime() {} Could anyone tell me why this is causing my JRE to crash? Thanks in advance.

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  • What is the use of Method Overloading in Java when it is achieved by changing the sequence of parameters in the argument list?

    - by MediumOne
    I was reading a Java training manual and it said that Method Overloading in Java can be achieved by having a different argument list. It also said that the argument list could differ in (i). Number of parameters (ii). Datatype of parameters (iii). Sequence of parameters My concern is about (iii). What is the use of trying to overload a method just by changing the sequence of parameters? I am unable to think of any benefits by this way.

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  • Multiple indexes for a Java Collection - most basic solution?

    - by chris_l
    Hi, I'm looking for the most basic solution to create multiple indexes on a Java Collection. Required functionality: When a Value is removed, all index entries associated with that value must be removed. Index lookup must be faster than linear search (at least as fast as a TreeMap). Side conditions: It should ideally work with JavaSE (6.0) alone - no extra libraries, if possible. If necessary, then only small (not something like Lucene), common and well tested libraries. No database! Of course, I could write a class that manages multiple Maps myself. But I'd like to know, if it can be done without - while still getting a simple usage similar to using a single indexed java.util.Map. Thanks, Chris

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  • How do I send data from Java to Flash locally?

    - by terence
    I have a website with a Java applet and a Flash application. I want the Java applet to send data to the Flash application locally. What's the best way to do this? The data I want to send are potentially large images (possibly up to 1MB in size). This means sending a base64 string to javascript and then to Flash would probably be too cumbersome. I don't want to have to contact external servers or anything; all of it should be possible locally and offline. Is there some easy way to just send this sort of data around? If I saved the file locally first, Flash wouldn't be able to access that, would it?

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  • Is it faster to use a complicated boolean to limit a ResultSet at the MySQL end or at the Java end?

    - by javanix
    Lets say I have a really big table filled with lots of data (say, enough not to fit comfortably in memory), and I want to analyze a subset of the rows. Is it generally faster to do: SELECT (column1, column2, ... , columnN) FROM table WHERE (some complicated boolean clause); and then use the ResultSet, or is it faster to do: SELECT (column1, column2, ... , columnN) FROM table; and then iterate over the ResultSet, accepting different rows based on a java version of your boolean condition? I think it comes down to whether the Java iterator/boolean evaluator is faster than the MySQL boolean evaluator.

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  • How do I prevent JAXB from generating Java from imported schema?

    - by Mark
    I've got two Java projects, both generate Java classes based on a schema definition, I'm using xjc to create the classes. My second project depends on a class from the first project, and in particular, one of the classes I'd like to generate in my second project needs to use one of the types from the first project. To accomplish this dependency at the schema level, I'm using a simple xsd:import to map the namespace to a particular schema. JAXB works just fine with this condition, except it also generates the first project's types in the second project. So after running have something like this: Project A +-- com.foo.bar +-- TypeA Project B +-- com.foo.asdf +-- TypeB +-- com.foo.bar +-- TypeA The second "TypeA" is undesirable, and I'd like to never generate it in the first place. How do I instruct JAXB not to generate the classes for "TypeA" that it finds as a result of the import statement?

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  • Books/resources on authentication and authorization in layered applications

    - by Tommy Jakobsen
    I've been trying to find resources and guidelines for implementing authentication and authorization in multiple layered architectures (C#), but haven't found any "best practices" or patterns to use. And I figured, that there must be some patterns for this, as it is a pretty important area? The application that we're developing, is layered traditionally, having data layer (Entity Framework 4) repositories domain layer service layer (can be WCF, with data transfer objects) multiple clients consuming the WCF service (ASP.NET [MVC], Silverlight, WPF) and clients accessing a service layer directly (no WCF) Are there books/articles/blogs that dig deeply into this area? Primarily about authorization such as handling multiple roles and attributes attached to users). It doesn’t have to be specific for the .NET Framework, but it would be preferred.

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  • How do you make your Java application memory efficient?

    - by Boune
    How do you optimize the heap size usage of an application that has a lot (millions) of long-lived objects? (big cache, loading lots of records from a db) Use the right data type Avoid java.lang.String to represent other data types Avoid duplicated objects Use enums if the values are known in advance Use object pools String.intern() (good idea?) Load/keep only the objects you need I am looking for general programming or Java specific answers. No funky compiler switch. Edit: Optimize the memory representation of a POJO that can appear millions of times in the heap. Use cases Load a huge csv file in memory (converted into POJOs) Use hibernate to retrieve million of records from a database Resume of answers: Use flyweight pattern Copy on write Instead of loading 10M objects with 3 properties, is it more efficient to have 3 arrays (or other data structure) of size 10M? (Could be a pain to manipulate data but if you are really short on memory...)

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  • How do I make a background thread in Java that allows the main application to exit completely? This

    - by Bob
    I have a Java application that creates a new thread to do some work. I can launch the new thread with no problems. When the "main" program terminates, I want the thread I created to keep running - which it does... But the problem is, when I run the main application from Eclipse or from Ant under Windows, control doesn't return unless the background process is killed. If I fork the main java process in ant, I want control to return to ant once the main thread is done with its work... But as it is, ant continues to wait until both the main process and the created thread are both terminated. How do I launch the thread in the background such that control will return to ant when the "main" application is finished? (By the way, when I run the same application under Linux, I am able to do this with no problems).

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  • inconsistency between Sun JRE javac and Eclipse java compiler?

    - by Jason S
    This confuses me. The following compiles fine under Eclipse. package com.example.gotchas; public class GenericHelper1 { static <T> T fail() throws UnsupportedOperationException { throw new UnsupportedOperationException(); } /** * just calls fail() * @return something maybe */ public boolean argh() { return fail(); } public static void main(String[] args) { // TODO Auto-generated method stub } } But if I try to do a clean build with ant, or at the command line with javac, I get this: src\com\example\gotchas\GenericHelper1.java:14: type parameters of <T>T cannot be determined; no unique maximal instance exists for type variable T with upper bounds boolean,java.lang.Object public boolean argh() { return fail(); } ^ 1 error what gives, and how do I fix it?

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  • Is Java serialization a tool to shrink the memory footprint?

    - by Pentius
    Hey folks, does serialization in Java always have to shrink the memory that is used to hold an object structure? Or is it likely that serialization will have higher costs? In other words: Is serialization a tool to shrink the memory footprint of object structures in Java? Edit I'm totally aware of what serialization was intended for, but thanks anyway :-) But you know, tools can be misused. My question is, whether it is a good tool to decrease the memory usage. So what reasons can you imagine, why memory usage should increase/decrease? What will happen in most cases?

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  • How to leave out some statements while executing java code?

    - by iamrohitbanga
    In C++ if we do not want some statements to compile into code that ships like assert function calls, we control their compilation through #ifndef preprocessor directives. How do we do this in Java? I have some System.out.println() statements for debugging which I would like to remove for the final code. one way is to make them execute conditionally under the affect of a boolean variable. Is there a better way of doing this? As I have a java swing application I can turn off the System.out.println statements without affecting the output. What is the method of doing this?

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  • Can functions like sin() be redefined, in Fortran, C or Java?

    - by EOL
    Can a mathematical function like sin() be redefined, in Fortran, C or Java code, while preserving the default behavior of other mathematical functions like cos()? Or can another function named sin() but that accepts different argument types be defined in addition to the built-in sin()? I am interested in general features of these languages (I am thinking of applications like the implementation of non-usual number algebras). I tried to define a sin() function in a Fortran 95 program, but the intrinsic sin() function was called instead… Is there a way around this? what about C and Java?

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  • How to make my Java Swing application a Client-Server application?

    - by Jonas
    I have made a Java Swing application. Now I would like to make it a Client-Server application. All clients should be notified when data on the server is changed, so I'm not looking for a Web Service. The Client-Server application will be run on a single LAN, it's a business application. The Server will contain a database, JavaDB. What technology and library is easiest to start with? Should I implement it from scratch using Sockets, or should I use Java RMI, or maybe JMS? Or are there other alternatives that are easier to start with? And is there any server library that I should use? Is Jetty an alternative?

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  • What is the best way to organize Java code since you can't pass by reference?

    - by Adam
    I'm learning how to code in Java after after coming from C. In C I always separated everything into individual functions to make the code easier to follow and edit. I was trying to do this in java but now since I realized that you can't use pointers, I am a bit confused as to what the best way to do this is. So for example I want to have a method that creates four alerts for me. So I pass it an alert builder that can then create the alerts. I can return them in an array, but in my code I already have the alerts individually named, and I would like to keep it that way so I wouldn't need to refer to them as alert[1], alert[2]... etc. So that means I would have to rename them, which would add additional code which would probably be longer than the code in the actual method! Am I thinking about this the right way? Is there anything I can do?

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  • How to use menu bars with different patterns?

    - by vahini
    I'm using Visual studio 2005, ASP.NET and C#. I want to use menu bars which have an active look to them when their respective target page is the one currently showing. Imagine a user clicks a menu item, navigation to the target page occurs and the menu item they selected is now differing, in say, color to that of the other items in the menu as a means to indicate this is the currently active location. How might one achieve this?

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