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  • Java - Could not find the main class?

    - by asmo
    I'm having a hard-time with a Java error. I'm getting this when double-clicking on my compiled project Jar file in order to run it: Could not find the main class: testPackage.testFrame. Program will exit. However, my main class is cleary defined in the project properties. Furthermore, everything works fine when I run the project directly from NetBeans. I'm using the ip2c.jar third-party library to determine countries from IP addresses. If I comment the class that is using the ip2c.jar file, I don't get the error. How can a third-party library be preventing the JVM from finding my main class?

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  • executing a class in remote jvm

    - by redzedi
    Hi All, I have a small test class that i want to run on a particular jvm that's already up and running (basically it's an web application running on Tomcat) . The reason i want to do this is i want to execute a small test class (with the main method and all) within that jvm so that i get the same environment (loaded and initialized classes) for my test class. Is it possible to indicate that ,say through a jvm parameter, that it should not initialize a new vm to execute my class but instead go and execute on the remote vm and show me the result here, on my console. So the local jvm acts as a kind of thin proxy ? I am not aware in case there are some tools that should make this possible ... also heard somewhere that java 6 jvm comes with an option like this , is that true ?? Please help me. Thanks,

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  • Enumeration classes in Java

    - by Crystal
    I have one class that declares an enumeration type as: public enum HOME_LOAN_TERMS {FIFTEEN_YEAR, THIRTY_YEAR}; Is this type usable in another class? I'm basically trying to complete a homework assignment where we have two types of loans, and one loanManager class. When I try to use the HOME_LOAN_TERMS.THIRTY_YEAR in my loanManager class that does not extend or implement the loan class, I get an error saying it 'cannot find symbol HOME_LOAN_TERMS.' So I did not know if my loanManager class needed to implement the two different loan classes. Thanks.

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  • Java: Make a method abstract for each extending class

    - by Martijn Courteaux
    Hi, Is there any keyword or design pattern for doing this? public abstract class Root { public abstract void foo(); } public abstract class SubClass extends Root { public void foo() { // Do something } } public class SubberClass extends SubClass { // Here is it not necessary to override foo() // So is there a way to make this necessary? // A way to obligate the developer make again the override } Thanks

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  • can a .class file be added to the urlpath of a URLClassLoader

    - by java_geek
    I have a custom class loader which extends from a URLClassLoader. I added a .class file to the urlpath using addURL(); but when i do a class.forname() using this loader i get a ClassNotFoundException. However, if i create a jar and add the jar to the urlpath, i do not get any exception. What can be added to the urlpath of a URLClassLoader usign addURL()

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  • Java Inheritance - Getting a Parameter from Parent Class

    - by Aaron
    I'm trying to take one parameter from the parent class of Car and add it to my array (carsParked), how can i do this? Parent Class public class Car { protected String regNo; //Car registration number protected String owner; //Name of the owner protected String carColor; /** Creates a Car object * @param rNo - registration number * @param own - name of the owner **/ public Car (String rNo, String own, String carColour) { regNo = rNo; owner = own; carColor = carColour; } /** @return The car registration number **/ public String getRegNo() { return regNo; } /** @return A String representation of the car details **/ public String getAsString() { return "Car: " + regNo + "\nColor: " + carColor; } public String getColor() { return carColor; } } Child Class public class Carpark extends Car { private String location; // Location of the Car Park private int capacity; // Capacity of the Car Park - how many cars it can hold private int carsIn; // Number of cars currently in the Car Park private String[] carsParked; /** Constructor for Carparks * @param loc - the Location of the Carpark * @param cap - the Capacity of the Carpark */ public Carpark (String locations, int room) { location = locations; capacity = room; } /** Records entry of a car into the car park */ public void driveIn() { carsIn = carsIn + 1; } /** Records the departure of a car from the car park */ public void driveOut() { carsIn = carsIn - 1; } /** Returns a String representation of information about the carpark */ public String getAsString() { return location + "\nCapacity: " + capacity + " Currently parked: " + carsIn + "\n*************************\n"; } }

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  • Java - Calling all methods of a class

    - by Thomas Eschemann
    I'm currently working on an application that has to render several Freemarker templates. So far I have a Generator class that handles the rendering. The class looks more or less like this: public class Generator { public static void generate(…) { renderTemplate1(); renderTemplate2(); renderTemplate3(); } private static void render(…) { // renders the template } private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; … } This works, but it doesn't really feel right. What I would like to do is create a class that holds all the renderTemplate...() methods and then call them dynamically from my Generator class. This would make it cleaner and easier to extend. I was thinking about using something like reflection, but it doesn't really feel like a good solution either. Any idea on how to implement this properly ?

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  • Longer execution through Java shell than console?

    - by czuk
    I have a script in Python which do some computations. When I run this script in console it takes about 7 minutes to complete but when I run it thought Java shell it takes three times longer. I use following code to execute the script in Java: this.p = Runtime.getRuntime().exec("script.py --batch", envp); this.input = new BufferedReader(new InputStreamReader(p.getInputStream())); this.output = new BufferedWriter(new OutputStreamWriter(p.getOutputStream())); this.error = new BufferedReader(new InputStreamReader(p.getErrorStream())); Do you have any suggestion why the Python script runs three time longer in Java than in a console? update The computation goes as follow: Java sends data to the Python. Python reads the data. Python generates a decision tree --- this is a long operation. Python sends a confirmation that the tree is ready. Java receives the confirmation. Later there is a series of communications between Java and Python but it takes only several second.

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  • What is the most simple way to execute java class every 30 seconds

    - by Gandalf StormCrow
    I've been reading about java/spring/hibernate and worked trough a "dummy" examples so I told my friend to recommend something a bit harder for me, and now I'm stuck.. here is the simplest class I could think of package spring.com.practice; public class Pitcher { private String shout; public String getShout() { return shout; } public void setShout(String shout) { this.shout = shout; } public void voice() { System.out.println(getShout()); } } What is the most simple way to print out something by calling metod voice() from spring beans, and do it repeadatly every 30 seconds lets say, here is what I've got so far : <bean id="simpleTrigger" class="org.springframework.scheduling.quartz.SimpleTriggerBean"> <property name="jobDetail" ref="jobSchedulerDetail" /> <property name="startDelay" value="0" /> <property name="repeatInterval" value="30" /> </bean> <bean class="org.springframework.scheduling.quartz.SchedulerFactoryBean"> <property name="schedulerName" value="pitcherScheduler" /> <property name="triggers"> <list> <ref bean="simpleTrigger" /> </list> </property> </bean> <bean id="pitcher" class="spring.com.practice.Pitcher"> <property name="shout" value="I started executing..."></property> </bean> And yes I'm trying to run this on Jboss 5, I'm building a project with maven.

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  • To "null" or not to "null" my class's attributes

    - by Helper Method
    When I write a class in Java, I like to initialize the attributes which are set to a default value directly and attributes which are set by the caller in the constructor, something like this: public class Stack<E> { private List<E> list; private size = 0; public Stack(int initialCapacity) { list = new ArrayList<E>(initialCapacity); } // remainder omitted } Now suppose I have a Tree class: public class Tree<E> { private Node<E> root = null; // no constructor needed, remainder omitted } Shall I set the root attribute to null, to mark that it is set to null by default, or omit the null value?

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  • Null Pointer Exception in my BroadcastReceiver class

    - by user1760007
    I want to search a db and toast a specific column on the startup of the phone. The app keeps crashing and getting an exception even though I feel as the code is correct. @Override public void onReceive(Context ctx, Intent intent) { Log.d("omg", "1"); DBAdapter do = new DBAdapter(ctx); Log.d("omg", "2"); Cursor cursor = do.fetchAllItems(); Log.d("omg", "3"); if (cursor.moveToFirst()) { Log.d("omg", "4"); do { Log.d("omg", "5"); String title = cursor.getString(cursor.getColumnIndex("item")); Log.d("omg", "6"); // i = cursor.getInt(cursor.getColumnIndex("id")); Toast.makeText(ctx, title, Toast.LENGTH_LONG).show(); } while (cursor.moveToNext()); } cursor.close(); } The frustrating part is that I don't see any of my "omg" logs show up in logcat. I only see when my application crashes. I get three lines of errors in logcat. 10-19 12:31:11.656: E/AndroidRuntime(1471): java.lang.RuntimeException: Unable to start receiver com.test.toaster.MyReciever: java.lang.NullPointerException 10-19 12:31:11.656: E/AndroidRuntime(1471): at com.test.toaster.DBAdapter.fetchAllItems(DBAdapter.java:96) 10-19 12:31:11.656: E/AndroidRuntime(1471): at com.test.toaster.MyReciever.onReceive(MyReciever.java:26) For anyone interested, here is my DBAdapter fetchAllItems code: public Cursor fetchAllItems() { return mDb.query(DATABASE_TABLE, new String[] { KEY_ITEM, KEY_PRIORITY, KEY_ROWID }, null, null, null, null, null); }

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  • Binding of JText fields value to Info Class

    - by Faizan Ahmed
    Is there any way to automatic binding of Swing JTextFields to Info Class. e.g private JTextField receiptId; private JTextField Id; public class Info { private string receiptId; private String id; // Getters and Setters } Is there any way when I entered values from Swing page then automatically values bind with my Info class? After that I can pass my Info object to other classes instead of sending all Text Fields.

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  • Java constructor using generic types

    - by Beer Me
    I'm having a hard time wrapping my head around Java generic types. Here's a simple piece of code that in my mind should work, but I'm obviously doing something wrong. Eclipse reports this error in BreweryList.java: The method breweryMethod() is undefined for the type <T> The idea is to fill a Vector with instances of objects that are a subclass of the Brewery class, so the invocation would be something like: BreweryList breweryList = new BreweryList(BrewerySubClass.class, list); BreweryList.java package com.beerme.test; import java.util.Vector; public class BreweryList<T extends Brewery> extends Vector<T> { public BreweryList(Class<T> c, Object[] j) { super(); for (int i = 0; i < j.length; i++) { T item = c.newInstance(); // breweryMethod() is an instance method // of Brewery, of which <T> is a subclass (right?) c.breweryMethod(); // "The method breweryMethod() is undefined // for the type <T>" } } } Brewery.java package com.beerme.test; public class Brewery { public Brewery() { super(); } protected void breweryMethod() { } } BrewerySubClass.java package com.beerme.test; public class BrewerySubClass extends Brewery { public BrewerySubClass() { super(); } public void brewerySubClassMethod() { } } I'm sure this is a complete-generics-noob question, but I'm stuck. Thanks for any tips!

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  • Batch Create Java Class Stubs

    - by user344639
    Given a list of potential class names: 1. Alaska . . . 50. Wyoming Is there a tool that will create empty java class files for each with supplied parameters? I'm thinking of something like the "New...Class" dialog in Eclipse, only on steriods. :-) Thanks in advance, Kyle

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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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  • Creating parameterized type object using annonymous class

    - by Andrei Fierbinteanu
    This might be a stupid question, but I just saw a question asking how to create a Type variable for a generic type. The consensus seemed to be that you should have a dummy method returning that type, and then use reflection to get it (in this case he wanted Map<String, String>). Something like this : public Map<String, String> dummy() { throw new Error(); } Type mapStringString = Class.forName("ThisClass").getMethod("dummy").getGenericReturnType(); My question is, not having used reflection that much, couldn't you just do something like: Type mapStringString = new ParameterizedType() { public Type getRawType() { return Map.class; } public Type getOwnerType() { return null; } public Type[] getActualTypeArguments() { return new Type[] { String.class, String.class }; } }; Would this work? If not, why not? And what are some of the dangers/problems if it does (besides being able to return some Type like Integer<String> which is obviously not possible.

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  • Is app stability unusually hard with Java?

    - by wrp
    Java's extensive libraries and tool support are appealing, but I've never tried developing with it because most Java applications I've used have been extremely buggy. This has me puzzled, because I hear that Java is the dominant platform for enterprise development. Maybe it's fine for server-side stuff but not desktop applications. I'm not talking about things like the long compile/startup times or the random latencies due to garbage collection. This is about things just going wrong. Some of the most common problems I see are: corrupted icons corrupted fonts, in menus usually and editing areas sometimes inaccurate framing of GUI elements dialogs sometimes popping up blank Maybe the problems are mostly with Swing. I've rarely used a Java application long enough to find deeper issues. I can think of a few possible explanations for what I've experienced: It's possible to write stable apps with Java, just harder. Java apps are always buggy and enterprise users just put up with it. Server-side apps are fine because just Swing is buggy. I'm living under a curse and need the services of a good witchdoctor.

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  • How does array class work in Java?

    - by oks16
    In Java, array is a class and extends Object. I am curious to know about this special array class. I don't find the class definition anywhere. Doing a getClass().getName() gives strange result. String[] array = new String[]{"one","two"}; System.out.println(array.getClass().getName()); // prints [Ljava.lang.String; I want to understand how array works under the hood. Is the array class definition hardcoded in the JVM? Any resources, books, links on this will be helpful. Thank you.

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  • Java constructor using generic types

    - by user37903
    I'm having a hard time wrapping my head around Java generic types. Here's a simple piece of code that in my mind should work, but I'm obviously doing something wrong. Eclipse reports this error in BreweryList.java: The method initBreweryFromObject() is undefined for the type <T> The idea is to fill a Vector with instances of objects that are a subclass of the Brewery class, so the invocation would be something like: BreweryList breweryList = new BreweryList(BrewerySubClass.class, list); BreweryList.java package com.beerme.test; import java.util.Vector; public class BreweryList<T extends Brewery> extends Vector<T> { public BreweryList(Class<T> c, Object[] j) { super(); for (int i = 0; i < j.length; i++) { T item = c.newInstance(); // initBreweryFromObject() is an instance method // of Brewery, of which <T> is a subclass (right?) c.initBreweryFromObject(); // "The method initBreweryFromObject() is undefined // for the type <T>" } } } Brewery.java package com.beerme.test; public class Brewery { public Brewery() { super(); } protected void breweryMethod() { } } BrewerySubClass.java package com.beerme.test; public class BrewerySubClass extends Brewery { public BrewerySubClass() { super(); } public void androidMethod() { } } I'm sure this is a complete-generics-noob question, but I'm stuck. Thanks for any tips!

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  • Covariant return types in Java enums

    - by Kelvin Chung
    As mentioned in another question on this site, something like this is not legal: public enum MyEnum { FOO { public Integer doSomething() { return (Integer) super.doSomething(); } }, BAR { public String doSomething() { return (String) super.doSomething(); } }; public Object doSomething(); } This is due to covariant return types apparently not working on enum constants (again breaking the illusion that enum constants are singleton subclasses of the enum type...) So, how about we add a bit of generics: is this legal? public enum MyEnum2 { FOO { public Class<Integer> doSomething() { return Integer.class; } }, BAR { public Class<String> doSomething() { return String.class; } }; public Class<?> doSomething(); } Here, all three return Class objects, yet the individual constants are "more specific" than the enum type as a whole...

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  • Reference variable to an object instantiated/initialized in another class in Java

    - by Alex
    The reason I'm asking is because I'm getting NullPointerException. I now this is very easy but I'm pretty new programming and find this a bit confusing. So say I have initialized an object in a class and want to access that same object from another class. Like now for instance I'm working on a small Chess game, in my model Game class I have an instance of Board, an object. Board, in turn, has an array of Squares. Square[][]. Game has board, board has Square[][]. Now if I want to access the Square[][] through the object board (in Game) of type Board. Do I just declare a variable with the same name and type or do I have to initialize it again? Board board OR Board board = new Board(); Note, I have already initialized board in the class Game so if I do it again, won't they be two totally different Board objects?

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  • how to get a constant in java with class

    - by vincent
    basically I need to get a constant for a class however I have no instance of the object but only its class. In PHP I would do constant(XYZ); Is there a similar way of retrieving a constant in JAVA? I need it to facilitate a dynamic getMethod call Class parameterType = Class.forName(class_name); object.setProperty(field name, field value, parameterType); the set property method would then get the correct method and set the specified property, however I cant get a method which has int as parameter type without using Interger.TYPE

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