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  • What's wrong with my logic (Java syntax)

    - by soda
    I'm trying to make a simple program that picks a random number and takes input from the user. The program should tell the user if the guess was hot (-/+ 5 units) or cold, but I never reach the else condition. Here's the section of code: public static void giveHint (int guess) { int min = guess - 5; int max = guess + 5; if ((guess > min) && (guess < max)) { System.out.println("Hot.."); } else { System.out.println("Cold.."); } }

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  • Selecting based on __key__ (a unique identifier) in google appengine [Java]

    - by Stavros
    I have public class QuantityType { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key key; @Persistent private String type; } I am trying to setup a query to get the right QuantityType by it's key gql = "select * from QuantityType where __key__='aght52oobW1hIHTWVzc2FnZRiyAQw'"; But its not working because BadFilterError: BadFilterError: invalid filter: key filter value must be a Key; received aght52oobW1hIHTWVzc2FnZRiyAQw (a str). I have also tried to use gql = "select * from QuantityType where __key__=='" + KeyFactory.stringToKey(qTypeKey)+"'"; but it's now working.. How can I get a specific object from my datastore by it's key?

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  • Java downcasting dilemma

    - by Shades88
    please have a look at this code here. class Vehicle { public void printSound() { System.out.print("vehicle"); } } class Car extends Vehicle { public void printSound() { System.out.print("car"); } } class Bike extends Vehicle{ public void printSound() { System.out.print("bike"); } } public class Test { public static void main(String[] args) { Vehicle v = new Car(); Bike b = (Bike)v; v.printSound(); b.printSound(); Object myObj = new String[]{"one", "two", "three"}; for (String s : (String[])myObj) System.out.print(s + "."); } } Executing this code will give ClassCastException saying inheritance.Car cannot be cast to inheritance.Bike. Now look at the line Object myObj = new String[]{"one", "two", "three"};. This line is same as Vehicle v = new Car(); right? In both lines we are assigning sub class object to super class reference variable. But downcasting String[]myObj is allowed but (Bike)v is not. Please help me understand what is going on around here.

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  • Java interface design

    - by Nayn
    Hi, I had an interface initially as below. public interface testMe { public Set<String> doSomething(); } public class A implements testMe { public Set<String> doSomething() { return // Set<String> } } I had similar classes implementing testMe. Now I have to add one more class which returns Set<Some Object> public class X implements testMe() { public Set<Some OBject> doSomething() { } } How could i add this mehtod in the interface without breaking existing classes? Thanks Nayn

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  • Help with method logic in Java, hw

    - by Crystal
    I have a Loan class that in its printPayment method, it prints the amortization table of a loan for a hw assignment. We are also to implement a print first payment method, and a print last payment method. Since my calculation is done in the printPayment method, I didn't know how I could get the value in the first or last iteration of the loop and print that amount out. One way I can think of is to write a new method that might return that value, but I wasn't sure if there was a better way. Here is my code: public abstract class Loan { public void setClient(Person client) { this.client = client; } public Person getClient() { return client; } public void setLoanId() { loanId = nextId; nextId++; } public int getLoanId() { return loanId; } public void setInterestRate(double interestRate) { this.interestRate = interestRate; } public double getInterestRate() { return interestRate; } public void setLoanLength(int loanLength) { this.loanLength = loanLength; } public int getLoanLength() { return loanLength; } public void setLoanAmount(double loanAmount) { this.loanAmount = loanAmount; } public double getLoanAmount() { return loanAmount; } public void printPayments() { double monthlyInterest; double monthlyPrincipalPaid; double newPrincipal; int paymentNumber = 1; double monthlyInterestRate = interestRate / 1200; double monthlyPayment = loanAmount * (monthlyInterestRate) / (1 - Math.pow((1 + monthlyInterestRate),( -1 * loanLength))); System.out.println("Payment Number | Interest | Principal | Loan Balance"); // amortization table while (loanAmount >= 0) { monthlyInterest = loanAmount * monthlyInterestRate; monthlyPrincipalPaid = monthlyPayment - monthlyInterest; newPrincipal = loanAmount - monthlyPrincipalPaid; loanAmount = newPrincipal; System.out.printf("%d, %.2f, %.2f, %.2f", paymentNumber++, monthlyInterest, monthlyPrincipalPaid, loanAmount); } } /* //method to print first payment public double getFirstPayment() { } method to print last payment public double getLastPayment() { }*/ private Person client; private int loanId; private double interestRate; private int loanLength; private double loanAmount; private static int nextId = 1; } Thanks!

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  • Java method get the inheriting type

    - by DrDro
    I have several classes that extend C and I would need a method that accepts any argument of type C. But in this method I would like to know if I'm dealing with A or B. * public A extends C public B extends C public void goForIt(C c)() If I cast how can I retrieve the type in a clean way (I just read using getClass or instanceof is often not the best way). PS: Fell free to edit an explicit title. *Sorry but I can't type closing braces

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  • Java Micro Edition (J2ME) - Update Record using recordstore enumeration

    - by Garbit
    Hi there, I have a record store of items which have (name, quantity, owner, status) Now when the user triggers an event i want to set the status of all items in my recordstore with "purchased" re = shoppingListStore.enumerateRecords(null, null, false); while (re.hasNextElement()) { // read current values of item byte [] itemRecord = re.nextRecord(); // deserialise byte array newItemObject.fromByteArray(itemRecord); // set item status to purchased newItemObject.setItemStatus("Purchased"); // create new bytearray and call newitemobject . tobytearray method to return a byte array of the object (using UTF8 encoded strings~) byte[] itemData = newItemObject.toByteArray(); // add new byte array to shoppinglist store shoppingListStore.setRecord(re.nextRecordId(), itemData, 0, itemData.length); } However I am overwriting the next record (using the nextRecordId), i've tried using nextRecordId - 1 but obviously this is out of bounds on the first one Hope you can help, Many thanks, andy

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  • Java Hibernate id auto increment

    - by vinise
    Hy I'v a little problem with hibernate on netbeans. I've a table with an Auto increment id : CREATE TABLE "DVD" ( "DVD_ID" INT not null primary key GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1), "TITLE" VARCHAR(150), "COM" LONG VARCHAR, "COVER" VARCHAR(150) ); But this auto increment is not properly detected with Reverse Engineering. I get a map file with this : <id name="dvdId" type="int"> <column name="DVD_ID" /> <generator class="assigned" /> </id> i've looked on google and on this site ... foud some stuf but i'm still stuck.. i've tried to add insert="false" update="false" on the map file but i get back : Caused by: org.xml.sax.SAXParseException: Attribute "insert" must be declared for element type "id". Anny help will be pleased Vincent

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  • Blackberry (Java) - Can't get KeyListener to work

    - by paullb
    I am trying to get the KeyListener working for Blackberry, but none of the Dialogs pop up indicating that a key has been pressed (see code below, each action has a dialog popup in them). Any ideas on what i might be doing wrong? public class CityInfo extends UiApplication implements KeyListener { static CityInfo application; public static void main(String[] args) { //create a new instance of the application //and start the application on the event thread application.enterEventDispatcher(); } public CityInfo() { //display a new screen application = new CityInfo(); pushScreen(new WorkflowDisplayScreen()); this.addKeyListener(this); } public boolean keyChar(char arg0, int arg1, int arg2) { // TODO Auto-generated method stub Dialog.alert("key pressed : " + arg0); return true; } public boolean keyDown(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyDown : " + keycode); return false; } public boolean keyRepeat(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyRepeat : " + keycode); return false; } public boolean keyStatus(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyStatus : " + keycode); return false; } public boolean keyUp(int keycode, int time) { Dialog.alert("keyUp : " + keycode); // TODO Auto-generated method stub return false; } } I also tried implementing keyChar on the MainScreen class but that did not yield any results either.

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  • How to close a java swing application from the code

    - by hstoerr
    What is the proper way to terminate a Swing application from the code, and what are the pitfalls? I'd tried to close my application automatically after a timer fires. But just calling dispose() on the JFrame didn't do the trick - the window vanished but the application did not terminate. However when closing the window with the close button, the application does terminate. What should I do?

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  • Java Simple ActionListener Questions

    - by Allen
    I have a main class in a program that launches another class that handles all the GUI stuff. In the GUI, i have a button that i need to attach an ActionListener to. The only problem is, the code to be executed needs to reside within the main class. How can i get the ActionPerformed() method to execute in the main class when a button is clicked elsewhere?

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  • Java - how to tell class of an object?

    - by lkm
    Given a method that accepts as a parameter a certain supertype. Is there any way, within that method, to determine the actual class of the object that was passed to it? I.e. if a subtype of the allowable parameter was actually passed, is there a way to find out which type it is? If this isn't possible can someone explain why not (from a language design perspective)? Thanks Update: just to make sure I was clear void doSomething(MyType myType) { //determine if myType is MyType OR one of its subclasses } Since the method signature specifies the parameter as being MyType, then how can one tell if the object is actually a subtype of MyType (and which one).

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  • Java JMenuItem Accelator Snow Leopard

    - by Jeremy McGee
    about = new JMenuItem("About"); about.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_A((Toolkit.getDefaultToolkit().getMenuShortcutMask())))); JMenu help = new JMenu("Help"); help.add(about); I was wondering why my aaccelerators were not working. I am running this in snow leopard with JavaSe-1.6 VM. They do work if I pull the menu down then try the key sequence. Thanks

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  • Using java class HttpsURLConnection

    - by KB22
    Hi all, I have a small piece of code which basically impements a HTTP-Client, i.e. it POSTS request and works with re RESPONSE. As long as HTTP is concenerned everthing work well. For some reason I now have to support HTTPS too. So here is briefly what I do in order to get a connection opened: URL url = new URL(serverAddress); HttpsURLConnection httpsConn = (HttpsURLConnection) url.openConnection(); This fails, stating: sun.net.www.protocol.https.HttpsURLConnectionImpl cannot be cast to com.sun.net.ssl.HttpsURLConnection I guess this is kinda trivial, but I just don't get what I'm doing wrong in this one... Googled it, and the code just looks right - not? any ideas are appreciated! thanks, K

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  • Java: how to use Google's HashBiMap?

    - by HH
    Keys are a file and a word. The file gives all words inside the file. The word gives all files having the word. I am unsure of the domain and co-domain parts. I want K to be of the type <String> and V to be of type <HashSet<FileObject>>. public HashBiMap<K<String>,V<HashSet<FileObject>>> wordToFiles = new HashBiMap<K<String>,V<HashSet<FileObject>>>(); public HashBiMap<K<String>,V<HashSet<FileObject>>> fileToWords = new HashBiMap<K<String>,V<HashSet<FileObject>>>(); Google's HashBiMap.

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  • I have a problem with the following Java code

    - by Sanjeev
    public class b { public static void main(String[] args) { byte b = 1; long l = 127; // b = b + l; // 1 if I try this then it does not compile b += l; // 2 if I try this then it does compile System.out.println(b); } } I am using this code but I have problem: I don't understand why b=b+l; is not compiling but if I write b+=l; then it compiles and runs. Please explain why this happens.

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  • Strange problem with simple multithreading program in Java

    - by Elizabeth
    Hello, I am just starting play with multithreading programming. I would like to my program show alternately character '-' and '+' but it doesn't. My task is to use synchronized keyword. As far I have: class FunnyStringGenerator{ private char c; public FunnyStringGenerator(){ c = '-'; } public synchronized char next(){ if(c == '-'){ c = '+'; } else{ c = '-'; } return c; } } class ThreadToGenerateStr implements Runnable{ FunnyStringGenerator gen; public ThreadToGenerateStr(FunnyStringGenerator fsg){ gen = fsg; } @Override public void run() { for(int i = 0; i < 10; i++){ System.out.print(gen.next()); } } } public class Main{ public static void main(String[] args) throws IOException { FunnyStringGenerator FSG = new FunnyStringGenerator(); ExecutorService exec = Executors.newCachedThreadPool(); for(int i = 0; i < 20; i++){ exec.execute(new ThreadToGenerateStr(FSG)); } } } EDIT: I also testing Thread.sleep in run method instead for loop.

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  • Java simple data format british time

    - by DD
    Hi, I am using simple date format to allow users to specify which time zone they are sending data in: DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss,z"); This works fine: e.g. df.parse("2009-05-16 11:07:41,GMT"); However, if someone is always sending time in London time (i.e. taking into account daylight savings), what would be the approriate time zone String to add? e.g. this doesnt work: df.parse("2009-05-16 11:07:41,Europe/London"); Thanks.

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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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  • help with reflections and annotations in java

    - by Yonatan
    Hello Internet ! I'm having trouble with doubling up on my code for no reason other than my own lack of ability to do it more efficiently... `for (Method curr: all){ if (curr.isAnnotationPresent(anno)){ if (anno == Pre.class){ for (String str : curr.getAnnotation(Pre.class).value()){ if (str.equals(method.getName()) && curr.getReturnType() == boolean.class && curr.getParameterTypes().length == 0){ toRun.add(curr); } } } if (anno == Post.class) { for (String str : curr.getAnnotation(Post.class).value()){ if (str.equals(method.getName()) && curr.getReturnType() == boolean.class && curr.getParameterTypes().length == 0){ toRun.add(curr); } } } } }` anno is a parameter - Class, and Pre and Post are my annotations, both have a value() which is an array of strings. Of course, this is all due to the fact that i let Eclipse auto fill code that i don't understand yet.

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  • Java heap size - will this work?

    - by UnCon
    Hi, I try this with NetBeans desktop application template - increasing heapsize (to 512 MiB) of executed .jar file. (I believe that NetBeans uses Singleton app by default - SingleFrameView) Will it work? public static void main(String[] args) { if (args == null) { args = new String[1]; args[0] = "Xmx512m"; } else { String[] tempArgs = new String[args.length+1]; for (int i=0; i<args.length; i++) { tempArgs[i] = args[i]; } tempArgs[tempArgs.length-1] = "Xmx512m"; args = tempArgs; } launch(MyApp.class, args); } }

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