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  • Casting and dynamic vs static type in Java

    - by XpdX
    I'm learning about static vs dynamic types, and I am to the point of understanding it for the most part, but this case still eludes me. If class B extends A, and I have: A x = new B(); Is the following allowed?: B y = x; Or is explicit casting required?: B y = (B)x; Thanks!

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  • Java Static Methods

    - by KP65
    Hello, I am wondering when to use static methods? Say If i have a class with a few getters and setters, a method or two, and i want those methods only to be invokable on an instance object of the class. Does this mean i should use a static method? e.g Obj x = new Obj(); x.someMethod or Obj.someMethod (is this the static way?) I'm rather confused!

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  • Java: Get Mainform object from JInternalFrame

    - by rodion
    Can I do this without reference to the object in the constructor? In other words, any class inherited from FrmTaoChild when creating must to add the button on the toolbar of the main window public class FrmTaoMain extends JFrame { JToolBar tbTask = new JToolBar(); public FrmTaoMain(String Caption) { super(Caption); ... FrmTaoChild FrmChild = new FrmTaoChild(tbTask,"test"); } } public class FrmTaoChild extends JInternalFrame { public FrmTaoChild(JToolBar tbTask, String Caption) { super (Caption); JButton btnTask = new JButton(Caption); tbTask.add(btnTask); } }

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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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  • How to add an image dynamically at runtime in java

    - by Brandon
    I've been trying to load up an image dynamically in runtime for the longest time and have taken a look at other posts on this site and have yet to find exactly the thing that will work. I am trying to load an image while my GUI is running (making it in runtime) and have tried various things. Right now, I have found the easiest way to create an image is to use a JLabel and add an ImageIcon to it. This has worked, but when I go to load it after the GUI is running, it fails saying there is a "NullPointerException". Here is the code I have so far: p = Runtime.getRuntime().exec("python C:\\FaceVACS\\roc.py " + "C:/FaceVACS/OutputCMC_" + target + ".txt " + "C:/FaceVACS/ROC_" + target + ".png"); Icon graph = new ImageIcon("C:\\FaceVACS\\OutputCMC_" + target + ".png"); roc_image.setIcon(graph); panel.add(roc_image); panel.revalidate(); gui.frame.pack(); I tried panel.validate(), panel.revalidate(), and I've also tried gui.getRootPane(), but I can't seem to find anything that will work. Any ideas would be helpful! Thanks

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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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  • Problem with Gregorian Calendar hour of day in java

    - by Leanne C
    hi, I'm using a Gregorian Calendar to set a specific date and time to an application using the set function of the Gregorian Calendar. When i use the getTime() method, it gives me the right output however when i try to access the Hour_Of_Day and Minute it gives a wrong number. Calendar time = new GregorianCalendar(); time.set(2010, Calendar.JANUARY, 1, 7, 20,0); hour = time.HOUR_OF_DAY; minute = time.MINUTE; The hour gives an output of 11 and the minute gives an a value of 12. Any suggestions on how to fix this? Thanks

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  • Java Future and infinite computation

    - by Chris
    I'm trying to optimize an (infinite) computation algorithm. I have an infinte Sum to calculate ( Summ_{n- infinity} (....) ) My idea was to create several threads using the Future < construct, then combine the intermediate results together. My problem hoewer is that I need a certain precision. So I need to constantly calculate the current result while other threads keep calculating. My question is: Is there some sort of result queue where each finished thread can put its results in, while a main thread can receive those results and then either lets the computation continues or terminate the whole ExecutorService? Any Help would really be appreciated! Thanks!

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  • Java - Class type from inside static initialization block

    - by DutrowLLC
    Is it possible to get the class type from inside the static initialization block? This is a simplified version of what I currently have:: class Person extends SuperClass { String firstName; static{ // This function is on the "SuperClass": // I'd for this function to be able to get "Person.class" without me // having to explicitly type it in but "this.class" does not work in // a static context. doSomeReflectionStuff(Person.class); // IN "SuperClass" } } This is closer to what I am doing, which is to initialize a data structure that holds information about the object and its annotations, etc... Perhaps I am using the wrong pattern? public abstract SuperClass{ static void doSomeReflectionStuff( Class<?> classType, List<FieldData> fieldDataList ){ Field[] fields = classType.getDeclaredFields(); for( Field field : fields ){ // Initialize fieldDataList } } } public abstract class Person { @SomeAnnotation String firstName; // Holds information on each of the fields, I used a Map<String, FieldData> // in my actual implementation to map strings to the field information, but that // seemed a little wordy for this example static List<FieldData> fieldDataList = new List<FieldData>(); static{ // Again, it seems dangerous to have to type in the "Person.class" // (or Address.class, PhoneNumber.class, etc...) every time. // Ideally, I'd liken to eliminate all this code from the Sub class // since now I have to copy and paste it into each Sub class. doSomeReflectionStuff(Person.class, fieldDataList); } }

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  • To instantiate BiMap Of google-collections in Java

    - by Masi
    How can you instantiate a Bimap of Google-collections? I know the thread. A sample of my code import com.google.common.collect.BiMap; public class UserSettings { private Map<String, Integer> wordToWordID; UserSettings() { this.wordToWordID = new BiMap<String. Integer>(); I get cannot instantiate the type BiMap<String, Integer>.

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  • How to make prevent public key inside jar to be saved using Java code

    - by Abhijith V R
    After signing a jar , we can retrieve the public keys from jar using Certificate[] cert = jarentry.getCertificates(); Once certificate is extracted we can save this to a new keystore as trusted cert. Once this is done , then second user can sign any jar using this certificate , isn't ? I want to distribute content as jars , contents will contain properties files for a application init. I want to make sure that an user is not capable to rebuilding the property files using the certificate he extracted from jarentry. In the code which reads the jar contents i am checking that jar is signed with my certificate only and also checking that jar is not tampered with . But the issue came to my mind that if i am able to extract the cerificate from jar then why don;t a third guy ? Can any one help me in this............

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  • Adding Listeners at runtime? - Java MVC

    - by Halo
    My model in my MVC pattern, generates components at runtime and gives them to the View to be displayed on the screen through update() method (you know, model is the observable and the view is the observer). But I also need to add listeners to these components, and the controller has the listener methods (because they say the MVC pattern is like this) and it's not involved in this update process. So I can't add the listeners at runtime, but only in the controller's constructor at startup. I've got an idea, that is making the controller the observer and then giving the data to the view, as well as adding the listeners. Do you think this would be OK?

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  • Java: why does extending need an empty constructor?

    - by HH
    I have classes SearchToUser and getFilesToWord. GetFilesToWord must inherit SearchToUser fields. Extending works if an empty construction in SearchToUser-class, otherwise: cannot find symbol symbol : constructor SearchToUser() location: class SearchToUser public class GetFilesToWord extends SearchToUser{ ^ 1 error make: *** [all] Error 1 I cannot understand why the empty constructor is required for extending.

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  • Java resource closing

    - by Bob
    Hi, I'm writing an app that connect to a website and read one line from it. I do it like this: try{ URLConnection connection = new URL("www.example.com").openConnection(); BufferedReader rd = new BufferedReader(new InputStreamReader(connection.getInputStream())); String response = rd.readLine(); rd.close(); }catch (Exception e) { //exception handling } Is it good? I mean, I close the BufferedReader in the last line, but I do not close the InputStreamReader. Should I create a standalone InputStreamReader from the connection.getInputStream, and a BufferedReader from the standalone InputStreamReader, than close all the two readers? I think it will be better to place the closing methods in the finally block like this: InputStreamReader isr = null; BufferedReader br = null; try{ URLConnection connection = new URL("www.example.com").openConnection(); isr = new InputStreamReader(connection.getInputStream()); br = new BufferedReader(isr); String response = br.readLine(); }catch (Exception e) { //exception handling }finally{ br.close(); isr.close(); } But it is ugly, because the closing methods can throw exception, so I have to handle or throw it. Which solution is better? Or what would be the best solution?

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  • J2EE fast track (Learning Enterprise Java real fast)

    - by IndexController
    Hello, We just started a new project in J2EE in our office and i am required to participate effectively. I mostly work on web applications and I use PHP/MySql but I also know J2SE and have written couple of standalone applications. I need help and advise on how i can learn J2ee very fast so that i can blend into the project without difficulties. I need help with book & tutorial recommendations and also links to resources. Thank you for your time.

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  • java regular expression

    - by changed
    Hi I have to create a regular expression for some path conversion. Example for path are //name:value /name:value // name:value /name:value /name:value /name:value//name:value thing is how to check for // or / at the start or middle of the string and how can i specify that name can contain any of this a-zA-Z and _ Path also contains white spaces. thanks-

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  • What's "@Override" there for in java?

    - by symfony
    public class Animal { public void eat() { System.out.println("I eat like a generic Animal."); } } public class Wolf extends Animal { @Override public void eat() { System.out.println("I eat like a wolf!"); } } Does @Override actually have some functionality or it's just kinda comment?

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  • Java - Custom PropertyEditorSupport to display units

    - by I82Much
    All, I'm trying to make the properties of my node have Units associated with the measure. ( I am using the JScience.org implementation of JSR 275) So for instance, public class Robot extends AbstractNode { // in kg float vehicleMass; @Override public Sheet createSheet() { Sheet s = Sheet.createDefault(); Sheet.Set set = s.createPropertiesSet(); try { PropertySupport.Reflection vehicleMassField = new PropertySupport.Reflection(this, float.class, "vehicleMass"); vehicleMassField.setValue("units", SI.KILOGRAMS); vehicleMassField.setName("vehicleMass"); set.put(vehicleMassField); PropertyEditorManager.registerEditor(float.class, UnitInPlaceEditor.class); } catch (NoSuchMethodException ex) { Exceptions.printStackTrace(ex); } s.put(set); return s; } } I want my UnitInPlaceEditor to append the units to the end of the string representation of the number, and when the field is clicked (enters edit mode) for the units to disappear and just the number becomes selected for editing. I can make the units appear, but I cannot get the units to disappear when the field enters editing mode. public class UnitsInplaceEditor extends PropertyEditorSupport implements ExPropertyEditor { private PropertyEnv pe; @Override public String getAsText() { // Append the unit by retrieving the stored value } @Override public void setAsText(String s) { // strip off the unit, parse out the number } public void attachEnv(PropertyEnv pe) { this.pe = pe; } } Here's a screenshot of the display - I like it like this.. but here's the value being edited; note the unit stays there. Basically I want one value (string) to be displayed in the field when the field is NOT being edited, and a different to be displayed when user starts editing the field. Barring that, I'd like to put a constant jlabel for the units (uneditable) to the right of the text field. Anyone know how to do this?

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  • Creating java class with annotated fields in runtime

    - by Sarmun
    The problem is that I need to create in runtime a class like this: public class Foo { @Bar int value0; @Bar int value1; @Bar int value2; .... } with number of fields being decided at runtime. I was looking at Javassist, and there you can create a new class, and add fields to it, but I haven't found a way to annotate those fields.

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