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  • Cutting down repeating code in c# Class

    - by Tom Gullen
    This is a wrapper for an API I'm working on, am I doing it sort of right? I'm not particularly fond of all the repeating code in the constructor, if someone can show me if I can reduce that it would be very helpful! public class WebWizForumVersion { // Properties of returned data public string Software { get; private set; } public string Version { get; private set; } public string APIVersion { get; private set; } public string Copyright { get; private set; } public string BoardName { get; private set; } public string URL { get; private set; } public string Email { get; private set; } public string Database { get; private set; } public string InstallationID { get; private set; } public bool NewsPad { get; private set; } public string NewsPadURL { get; private set; } public WebWizForumVersion(XmlReader Data) { try { Data.ReadToFollowing("Software"); this.Software = Data.ReadElementContentAsString(); Data.ReadToFollowing("Version"); this.Version = Data.ReadElementContentAsString(); Data.ReadToFollowing("ApiVersion"); this.APIVersion = Data.ReadElementContentAsString(); Data.ReadToFollowing("Copyright"); this.Copyright = Data.ReadElementContentAsString(); Data.ReadToFollowing("BoardName"); this.BoardName = Data.ReadElementContentAsString(); Data.ReadToFollowing("URL"); this.URL = Data.ReadElementContentAsString(); Data.ReadToFollowing("Email"); this.Email = Data.ReadElementContentAsString(); Data.ReadToFollowing("Database"); this.Database = Data.ReadElementContentAsString(); Data.ReadToFollowing("InstallID"); this.InstallationID = Data.ReadElementContentAsString(); Data.ReadToFollowing("NewsPad"); this.NewsPad = bool.Parse(Data.ReadElementContentAsString()); Data.ReadToFollowing("NewsPadURL"); this.NewsPadURL = Data.ReadElementContentAsString(); } catch (Exception e) { } } }

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  • java: useful example of a shutdown hook?

    - by Jason S
    I'm trying to make sure my Java application takes reasonable steps to be robust, and part of that involves shutting down gracefully. I am reading about shutdown hooks and I don't actually get how to make use of them in practice. Is there a practical example out there? Let's say I had a really simple application like this one below, which writes numbers to a file, 10 to a line, in batches of 100, and I want to make sure a given batch finishes if the program is interrupted. I get how to register a shutdown hook but I have no idea how to integrate that into my application. Any suggestions? package com.example.test.concurrency; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.PrintWriter; public class GracefulShutdownTest1 { final private int N; final private File f; public GracefulShutdownTest1(File f, int N) { this.f=f; this.N = N; } public void run() { PrintWriter pw = null; try { FileOutputStream fos = new FileOutputStream(this.f); pw = new PrintWriter(fos); for (int i = 0; i < N; ++i) writeBatch(pw, i); } catch (FileNotFoundException e) { e.printStackTrace(); } finally { pw.close(); } } private void writeBatch(PrintWriter pw, int i) { for (int j = 0; j < 100; ++j) { int k = i*100+j; pw.write(Integer.toString(k)); if ((j+1)%10 == 0) pw.write('\n'); else pw.write(' '); } } static public void main(String[] args) { if (args.length < 2) { System.out.println("args = [file] [N] " +"where file = output filename, N=batch count"); } else { new GracefulShutdownTest1( new File(args[0]), Integer.parseInt(args[1]) ).run(); } } }

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  • Error with my Android Application httpGet

    - by Coombes
    Basically I'm getting a strange issue with my Android application, it's supposed to grab a JSON Array and print out some values, the class looks like this: ShowComedianActivity.class package com.example.connecttest; public class ShowComedianActivity extends Activity{ TextView name; TextView add; TextView email; TextView tel; String id; // Progress Dialog private ProgressDialog pDialog; //JSON Parser class JSONParser jsonParser = new JSONParser(); // Single Comedian url private static final String url_comedian_details = "http://86.9.71.17/connect/get_comedian_details.php"; // JSON Node names private static final String TAG_SUCCESS = "success"; private static final String TAG_COMEDIAN = "comedian"; private static final String TAG_ID = "id"; private static final String TAG_NAME = "name"; private static final String TAG_ADDRESS = "address"; private static final String TAG_EMAIL = "email"; private static final String TAG_TEL = "tel"; public void onCreate(Bundle savedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.show_comedian); // Getting Comedian Details from intent Intent i = getIntent(); // Getting id from intent id = i.getStringExtra(TAG_ID); new GetComedianDetails().execute(); } class GetComedianDetails extends AsyncTask<String, String, String>{ protected void onPreExecute(){ super.onPreExecute(); pDialog = new ProgressDialog(ShowComedianActivity.this); pDialog.setMessage("Fetching Comedian details. Please wait..."); pDialog.setIndeterminate(false); pDialog.setCancelable(true); pDialog.show(); } @Override protected String doInBackground(String... params) { runOnUiThread(new Runnable(){ public void run(){ int success; try{ //Building parameters List<NameValuePair> params = new ArrayList<NameValuePair>(); params.add(new BasicNameValuePair("id",id)); // Getting comedian details via HTTP request // Uses a GET request JSONObject json = jsonParser.makeHttpRequest(url_comedian_details, "GET", params); // Check Log for json response Log.d("Single Comedian details", json.toString()); //JSON Success tag success = json.getInt(TAG_SUCCESS); if(success == 1){ // Succesfully received product details JSONArray comedianObj = json.getJSONArray(TAG_COMEDIAN); //JSON Array // get first comedian object from JSON Array JSONObject comedian = comedianObj.getJSONObject(0); // comedian with id found name = (TextView) findViewById(R.id.name); add = (TextView) findViewById(R.id.add); email = (TextView) findViewById(R.id.email); tel = (TextView) findViewById(R.id.tel); // Set text to details name.setText(comedian.getString(TAG_NAME)); add.setText(comedian.getString(TAG_ADDRESS)); email.setText(comedian.getString(TAG_EMAIL)); tel.setText(comedian.getString(TAG_TEL)); } } catch (JSONException e){ e.printStackTrace(); } } }); return null; } } } And my JSON Parser class looks like: package com.example.connecttest; public class JSONParser { static InputStream is = null; static JSONObject jObj = null; static String json = ""; // constructor public JSONParser() { } // function get json from url // by making HTTP POST or GET method public JSONObject makeHttpRequest(String url, String method, List<NameValuePair> params) { // Making HTTP request try { // check for request method if(method == "POST"){ // request method is POST // defaultHttpClient DefaultHttpClient httpClient = new DefaultHttpClient(); HttpPost httpPost = new HttpPost(url); httpPost.setEntity(new UrlEncodedFormEntity(params)); HttpResponse httpResponse = httpClient.execute(httpPost); HttpEntity httpEntity = httpResponse.getEntity(); is = httpEntity.getContent(); }else if(method == "GET"){ // request method is GET DefaultHttpClient httpClient = new DefaultHttpClient(); String paramString = URLEncodedUtils.format(params, "utf-8"); url += "?" + paramString; HttpGet httpGet = new HttpGet(url); HttpResponse httpResponse = httpClient.execute(httpGet); HttpEntity httpEntity = httpResponse.getEntity(); is = httpEntity.getContent(); } } catch (UnsupportedEncodingException e) { e.printStackTrace(); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } try { BufferedReader reader = new BufferedReader(new InputStreamReader( is, "iso-8859-1"), 8); StringBuilder sb = new StringBuilder(); String line = null; while ((line = reader.readLine()) != null) { sb.append(line + "\n"); } is.close(); json = sb.toString(); } catch (Exception e) { Log.e("Buffer Error", "Error converting result " + e.toString()); } // try parse the string to a JSON object try { jObj = new JSONObject(json); } catch (JSONException e) { Log.e("JSON Parser", "Error parsing data " + e.toString()); } // return JSON String return jObj; } } Now when I run a debug it's querying the correct address with ?id=1 on the end of the URL, and when I navigate to that url I get the following JSON Array: {"success":1,"comedian":[{"id":"1","name":"Michael Coombes","address":"5 Trevethenick Road","email":"[email protected]","tel":"xxxxxxxxxxxx"}]} However my app just crashes, the log-cat report looks like this: 03-22 02:05:02.140: E/Trace(3776): error opening trace file: No such file or directory (2) 03-22 02:05:04.590: E/AndroidRuntime(3776): FATAL EXCEPTION: main 03-22 02:05:04.590: E/AndroidRuntime(3776): android.os.NetworkOnMainThreadException 03-22 02:05:04.590: E/AndroidRuntime(3776): at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1117) 03-22 02:05:04.590: E/AndroidRuntime(3776): at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:84) 03-22 02:05:04.590: E/AndroidRuntime(3776): at libcore.io.IoBridge.connectErrno(IoBridge.java:127) 03-22 02:05:04.590: E/AndroidRuntime(3776): at libcore.io.IoBridge.connect(IoBridge.java:112) 03-22 02:05:04.590: E/AndroidRuntime(3776): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192) 03-22 02:05:04.590: E/AndroidRuntime(3776): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:459) 03-22 02:05:04.590: E/AndroidRuntime(3776): at java.net.Socket.connect(Socket.java:842) 03-22 02:05:04.590: E/AndroidRuntime(3776): at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:119) 03-22 02:05:04.590: E/AndroidRuntime(3776): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:144) 03-22 02:05:04.590: E/AndroidRuntime(3776): at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164) 03-22 02:05:04.590: E/AndroidRuntime(3776): at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119) 03-22 02:05:04.590: E/AndroidRuntime(3776): at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360) 03-22 02:05:04.590: E/AndroidRuntime(3776): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555) 03-22 02:05:04.590: E/AndroidRuntime(3776): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487) 03-22 02:05:04.590: E/AndroidRuntime(3776): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465) 03-22 02:05:04.590: E/AndroidRuntime(3776): at com.example.connecttest.JSONParser.makeHttpRequest(JSONParser.java:62) 03-22 02:05:04.590: E/AndroidRuntime(3776): at com.example.connecttest.ShowComedianActivity$GetComedianDetails$1.run(ShowComedianActivity.java:89) 03-22 02:05:04.590: E/AndroidRuntime(3776): at android.os.Handler.handleCallback(Handler.java:615) 03-22 02:05:04.590: E/AndroidRuntime(3776): at android.os.Handler.dispatchMessage(Handler.java:92) 03-22 02:05:04.590: E/AndroidRuntime(3776): at android.os.Looper.loop(Looper.java:137) 03-22 02:05:04.590: E/AndroidRuntime(3776): at android.app.ActivityThread.main(ActivityThread.java:4745) 03-22 02:05:04.590: E/AndroidRuntime(3776): at java.lang.reflect.Method.invokeNative(Native Method) 03-22 02:05:04.590: E/AndroidRuntime(3776): at java.lang.reflect.Method.invoke(Method.java:511) 03-22 02:05:04.590: E/AndroidRuntime(3776): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 03-22 02:05:04.590: E/AndroidRuntime(3776): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 03-22 02:05:04.590: E/AndroidRuntime(3776): at dalvik.system.NativeStart.main(Native Method) From this I'm guessing the error is in the jsonParser.makeHttpRequest however I can't for the life of me figure out what's going wrong and was hoping someone brighter than I could illuminate me.

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  • How to achieve interaction between GUI class with logic class

    - by volting
    Im new to GUI programming, and haven't done much OOP. Im working on a basic calculator app to help me learn GUI design and to brush up on OOP. I understand that anything GUI related should be kept seperate from the logic, but Im unsure how to implement interaction between logic an GUI classes when needed i.e. basically passing variables back and forth... Im using TKinter and when I pass a tkinter variable to my logic it only seems to hold the string PY_VAR0. def on_equal_btn_click(self): self.entryVariable.set(self.entryVariable.get() + "=") calculator = Calc(self.entryVariable) self.entryVariable.set(calculator.calculate()) Im sure that im probably doing something fundamentally wrong and probabaly really stupid, I spent a considerable amount of time experimenting (and searching for answers online) but Im getting no where. Any help would be appreciated. Thanks, V The Full Program (well just enough to show the structure..) import Tkinter class Gui(Tkinter.Tk): def __init__(self,parent): Tkinter.Tk.__init__(self,parent) self.parent = parent self.initialize() def initialize(self): self.grid() self.create_widgets() """ grid config """ #self.grid_columnconfigure(0,weight=1,pad=0) self.resizable(False, False) def create_widgets(self): """row 0 of grid""" """Create Text Entry Box""" self.entryVariable = Tkinter.StringVar() self.entry = Tkinter.Entry(self,width=30,textvariable=self.entryVariable) self.entry.grid(column=0,row=0, columnspan = 3 ) self.entry.bind("<Return>", self.on_press_enter) """create equal button""" equal_btn = Tkinter.Button(self,text="=",width=4,command=self.on_equal_btn_click) equal_btn.grid(column=3, row=0) """row 1 of grid""" """create number 1 button""" number1_btn = Tkinter.Button(self,text="1",width=8,command=self.on_number1_btn_click) number1_btn.grid(column=0, row=1) . . . def on_equal_btn_click(self): self.entryVariable.set(self.entryVariable.get() + "=") calculator = Calc(self.entryVariable) self.entryVariable.set(calculator.calculate()) class Calc(): def __init__(self, equation): self.equation = equation def calculate(self): #TODO: parse string and calculate... return self.equation if __name__ == "__main__": app = Gui(None) app.title('Calculator') app.mainloop()

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  • Cast base class object to derived class

    - by Popgalop
    Lets say I have two classes, animal and dog like this. class Animal { }; class Dog : public Animal { }; And I have an animal object named animal, that is actually an instance of dog, how would I cast it back to dog? This may seem like an odd question, but I need it because I am writing a programming language interpreter, and on the stack everything is stored as a BaseObject, and all the other datatypes extend BaseObject. How would I cast the base object from the stack, to a specific data type? I have tried something like this Dog dog = static_cast<Dog>(animal); But it gives me an error 1>------ Build started: Project: StackTests, Configuration: Debug Win32 ------ 1> StackTests.cpp 1>c:\users\owner\documents\visual studio 2012\projects\stacktests\stacktests\stacktests.cpp(173): error C2440: 'static_cast' : cannot convert from 'Animal' to 'Dog' 1> No constructor could take the source type, or constructor overload resolution was ambiguous 1>c:\users\owner\documents\visual studio 2012\projects\stacktests\stacktests\stacktests.cpp(173): error C2512: 'Dog' : no appropriate default constructor available ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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  • Override ToString() in your Classes

    - by psheriff
    One of the reasons I love teaching is because of the questions that I get from attendees. I was giving a presentation at DevConnections and was showing a collection of Product objects. When I hovered over the variable that contained the collection, it looked like Figure 2. As you can see in the collection, I have actual product names of my videos from www.pdsa.com/videos being displayed. To get your data to appear in the data tips you must override the ToString() method in your class. To illustrate this, take the following simple Product class shown below: public class Product{  public string ProductName { get; set; }  public int ProductId { get; set; }} This class does not have an override of the ToString() method so if you create a collection of Product objects you will end up with data tips that look like Figure 1. Below is the code I used to create a collection of Product objects. I have shortened the code in this blog, but you can get the full source code for this sample by following the instructions at the bottom of this blog entry. List<Product> coll = new List<Product>();Product prod; prod = new Product()  { ProductName = "From Zero to HTML 5 in 60 Minutes",     ProductId = 1 };coll.Add(prod);prod = new Product()   { ProductName = "Architecting Applications …",     ProductId = 2 };coll.Add(prod);prod = new Product()  { ProductName = "Introduction to Windows Phone Development",    ProductId = 3 };coll.Add(prod);prod = new Product()   { ProductName = "Architecting a Business  …",     ProductId = 4 };coll.Add(prod);......   Figure 1: Class without overriding ToString() Now, go back to the Product class and add an override of the ToString() method as shown in the code listed below: public class Product{  public string ProductName { get; set; }  public int ProductId { get; set; }   public override string ToString()  {    return ProductName;  }} In this simple sample, I am just returning the ProductName property. However, you can create a whole string of information if you wish to display more data in your data tips. Just concatenate any properties you want from your class and return that string. When you now run the application and hover over the collection object you will now see something that looks like Figure 2. Figure 2: Overriding ToString() in your Class Another place the ToString() override comes in handy is if you forget to use a DisplayMemberPath in your ListBox or ComboBox. The ToString() method is called automatically when a class is bound to a list control. Summary You should always override the ToString() method in your classes as this will help you when debugging your application. Seeing relevant data immediately in the data tip without having to drill down one more layer and maybe scroll through a complete list of properties should help speed up your development process. NOTE: You can download the sample code for this article by visiting my website at http://www.pdsa.com/downloads. Select “Tips & Tricks”, then select “Override ToString” from the drop down list.  

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  • Better way to generate enemies of different sub-classes

    - by KDiTraglia
    So lets pretend I have an enemy class that has some generic implementation and inheriting from it I have all the specific enemies of my game. There are points in my code that I need to check whether an enemy is a specific type, but in Java I have found no easier way than this monstrosity... //Must be a better way to do this if ( enemy.class.isAssignableFrom(Ninja.class) ) { ... } My partner on the project saw these and changed them to use an enum system instead public class Ninja extends Enemy { //EnemyType is an enum containing all our enemy types public EnemyType = EnemyTypes.NINJA; } if (enemy.EnemyType = EnemyTypes.NINJA) { ... } I also have found no way to generate enemies on varying probabilities besides this for (EnemyTypes types : enemyTypes) { if ( (randomNext = (randomNext - types.getFrequency())) < 0 ) { enemy = createEnemy(types.getEnemyType()); break; } } private static Enemy createEnemy(EnemyType type) { switch (type) { case NINJA: return new Ninja(new Vector2D(rand.nextInt(getScreenWidth()), 0), determineSpeed()); case GORILLA: return new Gorilla(new Vector2D(rand.nextInt(getScreenWidth()), 0), determineSpeed()); case TREX: return new TRex(new Vector2D(rand.nextInt(getScreenWidth()), 0), determineSpeed()); //etc } return null } I know java is a little weak at dynamic object creation, but is there a better way to implement this in a way such like this for (EnemyTypes types : enemyTypes) { if ( (randomNext = (randomNext - types.getFrequency())) < 0 ) { //Change enemyTypes to hold the classes of the enemies I can spawn enemy = types.getEnemyType().class.newInstance() break; } } Is the above possible? How would I declare enemyTypes to hold the classes if so? Everything I have tried so far as generated compile errors and general frustration, but I figured I might ask here before I completely give up to the huge mass that is the createEveryEnemy() method. All the enemies do inherit from the Enemy class (which is what the enemy variable is declared as). Also is there a better way to check which type a particular enemy that is shorter than enemy.class.isAssignableFrom(Ninja.class)? I'd like to ditch the enums entirely if possible, since they seem repetitive when the class name itself holds that information.

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  • In MVC , DAO should be called from Controller or Model

    - by tito
    I have seen various arguments against the DAO being called from the Controller class directly and also the DAO from the Model class.Infact I personally feel that if we are following the MVC pattern , the controller should not coupled with the DAO , but the Model class should invoke the DAO from within and controller should invoke the model class.Why because , we can decouple the model class apart from a webapplication and expose the functionalities for various ways like for a REST service to use our model class. If we write the DAO invocation in the controller , it would not be possible for a REST service to reuse the functionality right ? I have summarized both the approaches below. Approach #1 public class CustomerController extends HttpServlet { proctected void doPost(....) { Customer customer = new Customer("xxxxx","23",1); new CustomerDAO().save(customer); } } Approach #2 public class CustomerController extends HttpServlet { proctected void doPost(....) { Customer customer = new Customer("xxxxx","23",1); customer.save(customer); } } public class Customer { ........... private void save(Customer customer){ new CustomerDAO().save(customer); } } Note- Here is what a definition of Model is : Model: The model manages the behavior and data of the application domain, responds to requests for information about its state (usually from the view), and responds to instructions to change state (usually from the controller). In event-driven systems, the model notifies observers (usually views) when the information changes so that they can react. I would need an expert opinion on this because I find many using #1 or #2 , So which one is it ?

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  • Object desing problem for simple school application

    - by Aragornx
    I want to create simple school application that provides grades,notes,presence,etc. for students,teachers and parents. I'm trying to design objects for this problem and I'm little bit confused - because I'm not very experienced in class designing. Some of my present objects are : class PersonalData() { private String name; private String surename; private Calendar dateOfBirth; [...] } class Person { private PersonalData personalData; } class User extends Person { private String login; private char[] password; } class Student extends Person { private ArrayList<Counselor> counselors = new ArrayList<>(); } class Counselor extends Person { private ArrayList<Student> children = new ArrayList<>(); } class Teacher extends Person { private ArrayList<ChoolClass> schoolClasses = new ArrayList<>(); private ArrayList<Subject> subjects = new ArrayList<>(); } This is of course a general idea. But I'm sure it's not the best way. For example I want that one person could be a Teacher and also a Parent(Counselor) and present approach makes me to have two Person objects. I want that user after successful logging in get all roles that it has (Student or Teacher or (Teacher & Parent) ). I think I should make and use some interfaces but I'm not sure how to do this right. Maybe like this: interface Role { } interface TeacherRole implements Role { void addGrade( Student student, Grade grade, [...] ); } class Teacher implements TeacherRole { private Person person; [...] } class User extends Person{ ArrayList<Role> roles = new ArrayList<>(); } Please if anyone could help me to make this right or maybe just point me to some literature/article that covers practical objects design.

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  • java: Read text file and store the info in an array using scanner class

    - by Amateur
    Hi, I have a text file include Student Grades like Kim $ 40 $ 45 Jack $ 35 $ 40 I'm trying to read this data from the text file and store the information into an array list using Scanner Class could any one guied me to write the code correctly ? Here is what I have so far public class ReadStudentsGrade { public static void main(String[] args) throws IOException { ArrayList stuRec = new ArrayList(); File file = new File("c:\\StudentGrade.txt"); try { Scanner scanner = new Scanner(file).useDelimiter("$"); while (scanner.hasNextLine()) { String stuName = scanner.nextLine(); int midTirmGrade = scanner.nextInt(); int finalGrade = scanner.nextInt(); System.out.println(stuName + " " + midTirmGrade + " " + finalGrade); } } catch (FileNotFoundException e) { e.printStackTrace(); } }

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  • Java: immutable Stack?

    - by HH
    I chose to use Stacks and Tables before knowing Collections has immutable empty things only for Set, Map and List. Because the size of table does not change after its init: Integer[] table = new Intger[0] I can use the zero-witdh table as an empty table. But I cannot use final or empty Stack to get immutable Stack: No immutability to Stack with Final import java.io.*; import java.util.*; public class TestStack{ public static void main(String[] args) { final Stack<Integer> test = new Stack<Integer>(); Stack<Integer> test2 = new Stack<Integer>(); test.push(37707); test2.push(80437707); //WHY is there not an error to remove an elment // from FINAL stack? System.out.println(test.pop()); System.out.println(test2.pop()); } } Java Api 5 for list interface shows that Stack is an implementing class for list and arraylist, here. The java.coccurrent pkg does not have any immutable Stack data structure. From Stack to some immutable data structure How to get immutable Stack data structure? Can I box it with list? Should I switch my current implementatios from stacks to Lists to get immutable? Which immutable data structure is Very fast with about similar exec time as Stack?

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  • Location of Java dump heap file?

    - by Jim Ferrans
    Well this is embarrassing ... I'm starting to play with the Eclipse Memory Analyzer to look for Java memory leaks on a Windows box. Step 1 is to obtain a heap dump file. To do this< I start my Java (javaw.exe) process from within Eclipse and connect to it with jconsole. Then on the jconsole MBeans tab I click the dumpHeap button. The first time I did this, I saw a pop-up saying it had created the heap dump file, but not giving its name or location. Now whenever I do a dumpHeap again while connected to a different javaw.exe process, jconsole says: Problem invoking dumpHeap : java.io.IOException: File exists and of course doesn't give its name or path. Where could it be? I've searched my C: drive (using cygwin command line tools) for files containing "hprof" or "java_pid" or "heapdump" and didn't find anything plausible. I've even used the Windows search to look for all files in my Eclipse workspace that have changed in the last day. I'm using the Sun Java 1.6 JVM, and don't have -XX:HeapDumpPath set.

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  • Java RMI method synchronization

    - by James Moore
    Hello, I have a class that is stored on the 'server' and multiple clients can call this method. This method returns a class. Now when clients call accessor methods within this class for example a set accessor method. I want the object on the server to be updated and synchronized across all the other clients. How do I use: public synchronized setStatus(String s) { this.status = s; } within java to achieve this. Thanks

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  • Java - Trying to log into website with invalid ssl certificate using httpclient

    - by PCBEEF
    I'm trying to log into site with invalid ssl certificate and I have the following code. I bypass the the invalid cert by using my all certificate and then bypass the invalid Hostname by using hostnameverifier. However, the hostnameverifier does not seem to work and I still get the error message javax.net.ssl.SSLException: hostname in certificate didn't match: The code is: public static void main(String[] args) { TrustManager[] trustAllCerts = new TrustManager[] { new X509TrustManager() { public java.security.cert.X509Certificate[] getAcceptedIssuers() { return null; } public void checkClientTrusted( java.security.cert.X509Certificate[] certs, String authType) { } public void checkServerTrusted( java.security.cert.X509Certificate[] certs, String authType) { } } }; HostnameVerifier hv = new HostnameVerifier() { public boolean verify(String urlHostName, SSLSession session) { System.out.println("Warning: URL Host: "+urlHostName+" vs. "+session.getPeerHost()); return true; } }; try { SSLContext sc = SSLContext.getInstance("SSL"); sc.init(null, trustAllCerts, new java.security.SecureRandom()); HttpsURLConnection.setDefaultSSLSocketFactory(sc.getSocketFactory()); HttpsURLConnection.setDefaultHostnameVerifier(hv); } catch (Exception e) { } try { DefaultHttpClient httpclient = new DefaultHttpClient(); HttpContext localContext = new BasicHttpContext(); List<NameValuePair> formparams = new ArrayList<NameValuePair>(); formparams.add(new BasicNameValuePair("username", "user")); formparams.add(new BasicNameValuePair("password", "pword")); UrlEncodedFormEntity entity; entity = new UrlEncodedFormEntity(formparams, "UTF-8"); HttpPost httppost = new HttpPost("https://www.mysite.com/"); httppost.setEntity(entity); HttpResponse response = httpclient.execute(httppost, localContext); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }

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  • Linker errors using LuaJava on OSX 10.5

    - by Daniel
    Hi, I'm having a bunch of problems getting this library to work on my OSX installation. In particular, I'd like to use it with a Java 1.6 VM but after I compile it up I get the following: java -cp "luajava-1.1.jar" org.keplerproject.luajava.Console Exception in thread "main" java.lang.UnsatisfiedLinkError: /Users/dharabor/src/luajava- 1.1/libluajava-1.1.jnilib: at java.lang.ClassLoader$NativeLibrary.load(Native Method) at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1822) at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1739) at java.lang.Runtime.loadLibrary0(Runtime.java:823) at java.lang.System.loadLibrary(System.java:1030) at org.keplerproject.luajava.LuaState.<clinit>(LuaState.java:92) at org.keplerproject.luajava.LuaStateFactory.newLuaState(LuaStateFactory.java:59) at org.keplerproject.luajava.Console.main(Console.java:49) I'm running OSX 10.5.8 with Lua 5.1.4 I've also changed my OSX default VM to 1.6.0 as so: /System/Library/Frameworks/JavaVM.framework/Home -> Versions/1.6.0/Home/ /System/Library/Frameworks/JavaVM.framework/Versions/Current -> 1.6.0/ /System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK -> 1.6.0/ What am I doing wrong? I notice when I use Java 1.5 everything works great. Except I don't want 1.5, I want 1.6.

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  • Constructor overloading in Java - best practice

    - by errr
    There are a few topics similar to this, but I couldn't find one with a sufficient answer. I would like to know what is the best practice for constructor overloading in Java. I already have my own thoughts on the subject, but I'd like to hear more advice. I'm referring to both constructor overloading in a simple class and constructor overloading while inheriting an already overloaded class (meaning the base class has overloaded constructors). Thanks :)

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  • Java Singleton Pattern

    - by Spencer
    I'm used the Singleton Design Pattern public class Singleton { private static final Singleton INSTANCE = new Singleton(); // Private constructor prevents instantiation from other classes private Singleton() {} public static Singleton getInstance() { return INSTANCE; } } My question is how do I create an object of class Singleton in another class? I've tried: Singleton singleton = new Singleton(); // error - constructor is private Singleton singleton = Singleton.getInstance(); // error - non-static method cannot be referenced from a static context What is the correct code? Thanks, Spencer

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  • Getting error while invoking java weblogic.WLST from C drive

    - by user3718817
    I am getting an error message when I try to invoke java weblogic.WLST monitor.py weblogic weblogic1 t3://localhost:7001 from below mentioned path. C:\Users\satish>java weblogic.WLST monitor.py weblogic weblogic1 t3://127.0.0.1:7001 error Error: Could not find or load main class weblogic.WLST But when I invoke the same command from weblogic home I am not getting any issues. Requesting you to help regarding this. Please find the below class path: C:\Oracle\Middleware\wlserver_10.3\server\bin>setWLSEnv.cmd Error: Could not find or load main class weblogic.WLST Note: I already set class path. Kindly advise where I am getting wrong. Or is there any way that I can invoke my Python script from anywhere?

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  • Books and resources for Java Performance tuning - when working with databases, huge lists

    - by Arvind
    Hi All, I am relatively new to working on huge applications in Java. I am working on a Java web service which is pretty heavily used by various clients. The service basically queries the database (hibernate) and then works with a lot of Lists (there are adapters to convert list returned from DB to the interface which the service publishes) and I am seeing lot of issues with the service like high CPU usage or high heap space. While I can troubleshoot the performance issues using a profiler, I want to actually learn about what all I need to take care when I actually write code. Like what kind of List to use or things like using StringBuilder instead of String, etc... Is there any book or blogs which I can refer which will help me while I write new services? Also my application is multithreaded - each service call from a client is a new thread, and I want to know some best practices around that area as well. I did search the web but I found many tips which are not relevant in the latest Java 6 releases, so wanted to know what kind of resources would help a developer starting out now on Java for heavily used applications. Arvind

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  • Why is the user.dir system property working in Java?

    - by Geo
    Almost every article I read told me that you can't have chdir in Java. The accepted answer to this question says you can't do it in Java. However, here's some of the stuff I tried : geo@codebox:~$ java -version java version "1.6.0_14" Java(TM) SE Runtime Environment (build 1.6.0_14-b08) Java HotSpot(TM) Client VM (build 14.0-b16, mixed mode, sharing) Here's a test class I'm using : import java.io.*; public class Ch { public static void main(String[] args) { System.out.println(new File(".").getAbsolutePath()); System.setProperty("user.dir","/media"); System.out.println(new File(".").getAbsolutePath()); } } geo@codebox:~$ pwd /home/geo geo@codebox:~$ java Ch /home/geo/. /media/. Please explain why this worked. Can I use this from now on and expect it to work the same way on all platforms?

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  • ByteBuffer recycling class

    - by Chris Dennett
    Hi everyone, I'm wonder how I'd code up a ByteBuffer recycling class that can get me a ByteBuffer which is at least as big as the specified length, and which can lock up ByteBuffer objects in use to prevent their use while they are being used by my code. This would prevent re-construction of DirectByteBuffers and such over and over, instead using existing ones. Is there an existing Java library which can do this very effectively? I know Javolution can work with object recycling, but does that extend to the ByteBuffer class in this context with the requirements set out? Cheers, Chris

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  • Java equivalent to VS solution file

    - by Chris
    I'm a C# guy trying to learn Java. I understand the syntax and the basic architecture of the Java platform, and have no problem doing smaller projects myself, but I'd really like to be able to download some open source projects to learn from the work of others. However, I'm running into a stumbling block that I can't seem to find any information on. When I download an open source .NET project, I can open the .sln file with visual studio and everything just loads. Sure, there's occasionally a missing reference or something, but there's really very little configuration required to get things going. I'm not sensing the same ease of use with Java. I'm using eclipse at the moment, and it feels like for every project I have to create a brand new Eclipse project using "create from existing source", and almost nothing compiles properly without significant reconfiguration. In the case of web projects, it's even worse, because Eclipse doesn't appear to support creating a web project from existing source. I have to create a standard Java project from source, then then apparently modify the project file to include the bindings for the web toolkit stuff to work properly. Assuming I want to be able to contribute to a project later on, I shouldn't have to be making such drastic changes to the file structure to get my IDE to a workable state. What am I missing?

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  • Java getMethod with superclass parameters in method

    - by Jonathon
    Given: class A { public void m(List l) { ... } } Let's say I want to invoke method m with reflection, passing an ArrayList as the parameter to m: List myList = new ArrayList(); A a = new A(); Method method = A.class.getMethod("m", new Class[] { myList.getClass() }); method.invoke(a, Object[] { myList }); The getMethod on line 3 will throw NoSuchMethodException because the runtime type of myList is ArrayList, not List. Is there a good generic way around this that doesn't require knowledge of class A's parameter types?

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  • Java FileLock for Reading and Writing

    - by bobtheowl2
    I have a process that will be called rather frequently from cron to read a file that has certain move related commands in it. My process needs to read and write to this data file - and keep it locked to prevent other processes from touching it during this time. A completely separate process can be executed by a user to (potential) write/append to this same data file. I want these two processes to play nice and only access the file one at a time. The nio FileLock seemed to be what I needed (short of writing my own semaphore type files), but I'm having trouble locking it for reading. I can lock and write just fine, but when attempting to create lock when reading I get a NonWritableChannelException. Is it even possible to lock a file for reading? Seems like a RandomAccessFile is closer to what I need, but I don't see how to implement that. Here is the code that fails: FileInputStream fin = new FileInputStream(f); FileLock fl = fin.getChannel().tryLock(); if(fl != null) { System.out.println("Locked File"); BufferedReader in = new BufferedReader(new InputStreamReader(fin)); System.out.println(in.readLine()); ... The exception is thrown on the FileLock line. java.nio.channels.NonWritableChannelException at sun.nio.ch.FileChannelImpl.tryLock(Unknown Source) at java.nio.channels.FileChannel.tryLock(Unknown Source) at Mover.run(Mover.java:74) at java.lang.Thread.run(Unknown Source) Looking at the JavaDocs, it says Unchecked exception thrown when an attempt is made to write to a channel that was not originally opened for writing. But I don't necessarily need to write to it. When I try creating a FileOutpuStream, etc. for writing purposes it is happy until I try to open a FileInputStream on the same file.

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  • Making Spring Data JPA work with DataNucleus (GAE) (Spring Boot)

    - by xybrek
    There are several hints that Spring Data works with Google App Engine like: http://tommysiu.blogspot.com/2014/01/spring-data-on-gae-part-1.html http://blog.eisele.net/2009/07/spring-300m3-on-google-appengine-with.html Much of the examples are not "Spring Boot" so I've been trying to retrofit things with it. However, I've been stuck with this error for days and days: [INFO] Caused by: java.lang.NullPointerException [INFO] at org.datanucleus.api.jpa.metamodel.SingularAttributeImpl.isVersion(SingularAttributeImpl.java:79) [INFO] at org.springframework.data.jpa.repository.support.JpaMetamodelEntityInformation.findVersionAttribute(JpaMetamodelEntityInformation.java:102) [INFO] at org.springframework.data.jpa.repository.support.JpaMetamodelEntityInformation.<init>(JpaMetamodelEntityInformation.java:79) [INFO] at org.springframework.data.jpa.repository.support.JpaEntityInformationSupport.getMetadata(JpaEntityInformationSupport.java:65) [INFO] at org.springframework.data.jpa.repository.support.JpaRepositoryFactory.getEntityInformation(JpaRepositoryFactory.java:149) [INFO] at org.springframework.data.jpa.repository.support.JpaRepositoryFactory.getTargetRepository(JpaRepositoryFactory.java:88) [INFO] at org.springframework.data.jpa.repository.support.JpaRepositoryFactory.getTargetRepository(JpaRepositoryFactory.java:68) [INFO] at org.springframework.data.repository.core.support.RepositoryFactorySupport.getRepository(RepositoryFactorySupport.java:158) [INFO] at org.springframework.data.repository.core.support.RepositoryFactoryBeanSupport.initAndReturn(RepositoryFactoryBeanSupport.java:224) [INFO] at org.springframework.data.repository.core.support.RepositoryFactoryBeanSupport.afterPropertiesSet(RepositoryFactoryBeanSupport.java:210) [INFO] at org.springframework.data.jpa.repository.support.JpaRepositoryFactoryBean.afterPropertiesSet(JpaRepositoryFactoryBean.java:92) [INFO] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$6.run(AbstractAutowireCapableBeanFactory.java:1602) [INFO] at java.security.AccessController.doPrivileged(Native Method) [INFO] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1599) [INFO] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1549) [INFO] ... 40 more Where, I'm trying to use Spring Data JPA with DataNucleus/AppEngine: @Configuration @ComponentScan @EnableJpaRepositories @EnableTransactionManagement class JpaApplicationConfig { private static final Logger logger = Logger .getLogger(JpaApplicationConfig.class.getName()); @Bean public EntityManagerFactory entityManagerFactory() { logger.info("Loading Entity Manager..."); return Persistence .createEntityManagerFactory("transactions-optional"); } @Bean public PlatformTransactionManager transactionManager() { logger.info("Loading Transaction Manager..."); final JpaTransactionManager txManager = new JpaTransactionManager(); txManager.setEntityManagerFactory(entityManagerFactory()); return txManager; } } I've tested Persistence.createEntityManagerFactory("transactions-optional"); to see if the app can persist using this EMF, well, it does, so I am sure that this EMF works fine. The problem is the "wiring" up with the Spring Data JPA, can anybody help?

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