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  • java serialization and final fields

    - by mdma
    I have an class defining an immutable value type that I now need to serialize. The immutability comes from the final fields which are set in the constructor. I've tried serializing, and it works (surprisingly?) - but I've no idea how. Here's an example of the class public class MyValueType implements Serializable { private final int value; private transient int derivedValue; public MyValueType(int value) { this.value = value; this.derivedValue = derivedValue(value); } // getters etc... } Given that the class doesn't have a no arg constructor, how can it be instantiated and the final field set? (An aside - I noticed this class particularly because IDEA wasn't generating a "no serialVersionUID" inspection warning for this class, yet successfully generated warnings for other classes that I've just made serializable.)

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  • How to serialize Java primitives using Jersey REST

    - by Olvagor
    In my application I use Jersey REST to serialize complex objects. This works quite fine. But there are a few method which simply return an int or boolean. Jersey can't handle primitive types (to my knowledge), probably because they're no annotated and Jersey has no default annotation for them. I worked around that by creating complex types like a RestBoolean or RestInteger, which simply hold an int or boolean value and have the appropriate annotations. Isn't there an easier way than writing these container objects?

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  • Java webapp: where/how to automatically set each picture's width/height

    - by NoozNooz42
    For several reasons, a lot of "webmaster guides" (like Google and Yahoo!'s webmaster guides/guidelines) repeats several times that it is better to always put the width and height attribute of the img tag. One of the most obvious reason is that the elements in the page won't seem to be "jumping around" to a new location after every picture is loaded (always setting the correct width/height sure gets rid of this behavior). And there are other reasons to follow these guidelines / best practices. So: if we consider that these are indeed good practices if there are a lot of pictures and they are changing often if pictures aren't changing between two .war re-deploy (that is: there's no user-contributed picture) if we don't want to manually edit all these width/height attributes How do we automatically/programmatically serve HTML pages where every img tag have their width/height attribute correctly set as the best practice recommend?

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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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  • java casting confusion

    - by Stardust
    Could anyone please tell me why the following casting is resulting in compile time error: Long l = (Long)Math.pow(5,2); But why not the following: long l = (long)Math.pow(5,2);

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  • Object Literals In Java?

    - by jjacquay712
    I am learning GWT for web development and came across a piece of code I can't really understand. helloBtn.addClickHandler(new ClickHandler() { public void onClick(ClickEvent event) { Window.alert("Hello!"); } }); If someone could explain to me what it is doing that would be great. Thanks, John

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  • [java] Trying to use ResourceBundle to fetch messages from external file

    - by bumperbox
    Essentially I would like to have a messages.properties files external to the jar files in my application. So that users can add languages and edit the files easily if my translations are wrong at the moment i use ResourceBundle.getBundle("package.MessageBundle"); But i would like to do something like this ResourceBundle.getBundle("lang/MessageBundle"); Where lang is a folder under my application installation directory. is this a good idea (if not, why not)? can someone point me in the right direction, or some sample code that does this thanks Alex

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  • Implementing Java Priority Queue

    - by Kay
    public class PriorityQueue<T> { private PriorityNode<T> head, tail; private int numItems; public PriorityQueue(){ numItems = 0; head=null; tail=null; } public void add(int priority, T value){ PriorityNode<T> newNode = new PriorityNode<T>(priority,value); if(numItems == 0){ head = newNode; tail = newNode; } else{ head.setNext(newNode); head = newNode; } } } Where PriorityNode is defined as: public class PriorityNode<T> implements Comparable<T> { private T value; private PriorityNode<T> next; private int priority; public PriorityNode(int priority,T newValue){ value = newValue; next = null; priority = 0; } public PriorityNode(T newValue){ value = newValue; next = null; priority = 0; } public void setPriority(int priority){ this.priority = priority; } public int getPriority(){ return this.priority; } public T getValue(){ return value; } public PriorityNode<T> getNext(){ return next; } public void setNext(PriorityNode<T> nextNode){ this.next = nextNode; } public void setValue(T newValue){ value = newValue; } public int compareTo(int pri) { // TODO Auto-generated method stub if(this.priority<pri){ return -1; } else if(this.priority == pri){ return 0; } else{ return 1; } } } I'm having a lot of difficulty using the Comparator here and implementing a priority queue - please point me in the right direction.

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  • Java: why can't iterate over an iterator?

    - by noamtm
    I read http://stackoverflow.com/questions/839178/why-is-javas-iterator-not-an-iterable and http://stackoverflow.com/questions/27240/why-arent-enumerations-iterable, but I still don't understand why this: void foo(Iterator<X> it) { for (X x : it) { bar(x); baz(x); } } was not made possible. In other words, unless I'm missing something, the above could have been nice and valid syntactic sugar for: void foo(Iterator<X> it) { for (X x; it.hasNext();) { x = it.next(); bar(x); baz(x); } }

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  • How to wrap Java String.format()?

    - by BlinK_
    Hey everyone, I would like to wrap the String.format() method with in my own Logger class. I can't figure a way how to pass arguments from my method to String.format(). public class Logger { public static void format(String format, Object... args) { print(String.format(format, args)); // <-- this gives an error obviously. } public static void print(String s) { System.out.println(s); } }

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  • org.apache.http.conn.HttpHostConnectException:Connection to http://172.20.38.143 refused

    - by Passion
    I have developed client server Application .I am accessing mysql with php running on my machine and client running on my cell which is connected to machine.WI-FI is also switched ON. Internet Permission are also added in Manifest file but then also the i encounter error 172.20.38.143 is IP OF MY MACHINE 06-01 13:20:10.391: W/System.err(11157): org.apache.http.conn.HttpHostConnectException: Connection to http://172.20.38.143 refused 06-01 13:20:10.401: W/System.err(11157): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:183) 06-01 13:20:10.401: W/System.err(11157): at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164) 06-01 13:20:10.401: W/System.err(11157): at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119) 06-01 13:20:10.401: W/System.err(11157): at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360) 06-01 13:20:10.401: W/System.err(11157): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:674) 06-01 13:20:10.401: W/System.err(11157): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:511) 06-01 13:20:10.401: W/System.err(11157): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:489) 06-01 13:20:10.401: W/System.err(11157): at nineandroid.net.example.library.JSONParser.getJSONFromUrl(JSONParser.java:42) 06-01 13:20:10.401: W/System.err(11157): at nineandroid.net.example.library.UserFunctions.registerUser(UserFunctions.java:59) 06-01 13:20:10.401: W/System.err(11157): at nineandroid.net.example.RegisterActivity$1.onClick(RegisterActivity.java:52) 06-01 13:20:10.411: W/System.err(11157): at android.view.View.performClick(View.java:3567) 06-01 13:20:10.411: W/System.err(11157): at android.view.View$PerformClick.run(View.java:14224) 06-01 13:20:10.411: W/System.err(11157): at android.os.Handler.handleCallback(Handler.java:605) 06-01 13:20:10.411: W/System.err(11157): at android.os.Handler.dispatchMessage(Handler.java:92) 06-01 13:20:10.411: W/System.err(11157): at android.os.Looper.loop(Looper.java:137) 06-01 13:20:10.411: W/System.err(11157): at android.app.ActivityThread.main(ActivityThread.java:4517) 06-01 13:20:10.411: W/System.err(11157): at java.lang.reflect.Method.invokeNative(Native Method) 06-01 13:20:10.411: W/System.err(11157): at java.lang.reflect.Method.invoke(Method.java:511) 06-01 13:20:10.411: W/System.err(11157): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993) 06-01 13:20:10.421: W/System.err(11157): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760) 06-01 13:20:10.421: W/System.err(11157): at dalvik.system.NativeStart.main(Native Method) 06-01 13:20:10.421: W/System.err(11157): Caused by: java.net.ConnectException: failed to connect to /172.20.38.143 (port 80): connect failed: ENETUNREACH (Network is unreachable) 06-01 13:20:10.431: W/System.err(11157): at libcore.io.IoBridge.connect(IoBridge.java:114) 06-01 13:20:10.431: W/System.err(11157): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192) 06-01 13:20:10.431: W/System.err(11157): at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:459) 06-01 13:20:10.431: W/System.err(11157): at java.net.Socket.connect(Socket.java:848) 06-01 13:20:10.431: W/System.err(11157): at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:119) 06-01 13:20:10.431: W/System.err(11157): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:144) 06-01 13:20:10.431: W/System.err(11157): ... 20 more 06-01 13:20:10.431: W/System.err(11157): Caused by: libcore.io.ErrnoException: connect failed: ENETUNREACH (Network is unreachable) 06-01 13:20:10.441: W/System.err(11157): at libcore.io.Posix.connect(Native Method) 06-01 13:20:10.441: W/System.err(11157): at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:85) 06-01 13:20:10.441: W/System.err(11157): at libcore.io.IoBridge.connectErrno(IoBridge.java:127) 06-01 13:20:10.441: W/System.err(11157): at libcore.io.IoBridge.connect(IoBridge.java:112) 06-01 13:20:10.441: W/System.err(11157): ... 25 more 06-01 13:20:10.441: E/Buffer Error(11157): Error converting result java.lang.NullPointerException 06-01 13:20:10.451: E/JSON Parser(11157): Error parsing data org.json.JSONException: End of input at character 0 of 06-01 13:20:10.451: D/AndroidRuntime(11157): Shutting down VM 06-01 13:20:10.451: W/dalvikvm(11157): threadid=1: thread exiting with uncaught exception (group=0x40c0aa68) 06-01 13:20:10.451: E/AndroidRuntime(11157): FATAL EXCEPTION: main 06-01 13:20:10.451: E/AndroidRuntime(11157): java.lang.NullPointerException 06-01 13:20:10.451: E/AndroidRuntime(11157): at nineandroid.net.example.RegisterActivity$1.onClick(RegisterActivity.java:56) 06-01 13:20:10.451: E/AndroidRuntime(11157): at android.view.View.performClick(View.java:3567) 06-01 13:20:10.451: E/AndroidRuntime(11157): at android.view.View$PerformClick.run(View.java:14224) 06-01 13:20:10.451: E/AndroidRuntime(11157): at android.os.Handler.handleCallback(Handler.java:605) 06-01 13:20:10.451: E/AndroidRuntime(11157): at android.os.Handler.dispatchMessage(Handler.java:92) 06-01 13:20:10.451: E/AndroidRuntime(11157): at android.os.Looper.loop(Looper.java:137) 06-01 13:20:10.451: E/AndroidRuntime(11157): at android.app.ActivityThread.main(ActivityThread.java:4517) 06-01 13:20:10.451: E/AndroidRuntime(11157): at java.lang.reflect.Method.invokeNative(Native Method) 06-01 13:20:10.451: E/AndroidRuntime(11157): at java.lang.reflect.Method.invoke(Method.java:511) 06-01 13:20:10.451: E/AndroidRuntime(11157): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993) 06-01 13:20:10.451: E/AndroidRuntime(11157): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760) 06-01 13:20:10.451: E/AndroidRuntime(11157): at dalvik.system.NativeStart.main(Native Method) UserFunctions.java to call jsonParser public class UserFunctions { private JSONParser jsonParser; private static String loginURL = "http://172.20.38.143/ah_login_api/"; private static String registerURL = "http://172.20.38.143/ah_login_api/"; private static String login_tag = "login"; private static String register_tag = "register"; // constructor public UserFunctions(){ jsonParser = new JSONParser(); } /** * function make Login Request * @param email * @param password * */ public JSONObject loginUser(String email, String password){ // Building Parameters List<NameValuePair> params = new ArrayList<NameValuePair>(); params.add(new BasicNameValuePair("tag", login_tag)); params.add(new BasicNameValuePair("email", email)); params.add(new BasicNameValuePair("password", password)); JSONObject json = jsonParser.getJSONFromUrl(loginURL, params); // return json // Log.e("JSON", json.toString()); return json; } /** * function make Login Request * @param name * @param email * @param password * */ public JSONObject registerUser(String name, String email, String password){ // Building Parameters List<NameValuePair> params = new ArrayList<NameValuePair>(); params.add(new BasicNameValuePair("tag", register_tag)); params.add(new BasicNameValuePair("name", name)); params.add(new BasicNameValuePair("email", email)); params.add(new BasicNameValuePair("password", password)); // getting JSON Object JSONObject json = jsonParser.getJSONFromUrl(registerURL, params); // return json return json; } /** * Function get Login status * */ public boolean isUserLoggedIn(Context context){ DatabaseHandler db = new DatabaseHandler(context); int count = db.getRowCount(); if(count > 0){ // user logged in return true; } return false; } /** * Function to logout user * Reset Database * */ public boolean logoutUser(Context context){ DatabaseHandler db = new DatabaseHandler(context); db.resetTables(); return true; } } jsonParser.java public class JSONParser { static InputStream is = null; static JSONObject jObj = null; static String json = ""; // constructor public JSONParser() { } public JSONObject getJSONFromUrl(String url, List<NameValuePair> params) { // Making HTTP request try { // 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(); } 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(); Log.e("JSON", json); } 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; } } RegisterActivity.java public class RegisterActivity extends Activity { Button btnRegister; Button btnLinkToLogin; EditText inputFullName; EditText inputEmail; EditText inputPassword; TextView registerErrorMsg; // JSON Response node names private static String KEY_SUCCESS = "success"; private static String KEY_UID = "uid"; private static String KEY_NAME = "name"; private static String KEY_EMAIL = "email"; private static String KEY_CREATED_AT = "created_at"; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.register); // Importing all assets like buttons, text fields inputFullName = (EditText) findViewById(R.id.registerName); inputEmail = (EditText) findViewById(R.id.registerEmail); inputPassword = (EditText) findViewById(R.id.registerPassword); btnRegister = (Button) findViewById(R.id.btnRegister); btnLinkToLogin = (Button) findViewById(R.id.btnLinkToLoginScreen); registerErrorMsg = (TextView) findViewById(R.id.register_error); // Register Button Click event btnRegister.setOnClickListener(new View.OnClickListener() { public void onClick(View view) { String name = inputFullName.getText().toString(); String email = inputEmail.getText().toString(); String password = inputPassword.getText().toString(); UserFunctions userFunction = new UserFunctions(); JSONObject json = userFunction.registerUser(name, email, password); // check for login response try { if (json.getString(KEY_SUCCESS) != null) { registerErrorMsg.setText(""); String res = json.getString(KEY_SUCCESS); if(Integer.parseInt(res) == 1){ // user successfully registred // Store user details in SQLite Database DatabaseHandler db = new DatabaseHandler(getApplicationContext()); JSONObject json_user = json.getJSONObject("user"); // Clear all previous data in database userFunction.logoutUser(getApplicationContext()); db.addUser(json_user.getString(KEY_NAME), json_user.getString(KEY_EMAIL), json.getString(KEY_UID), json_user.getString(KEY_CREATED_AT)); // Launch Dashboard Screen Intent dashboard = new Intent(getApplicationContext(), DashboardActivity.class); // Close all views before launching Dashboard dashboard.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); startActivity(dashboard); // Close Registration Screen finish(); }else{ // Error in registration registerErrorMsg.setText("Error occured in registration"); } } } catch (JSONException e) { e.printStackTrace(); } } }); // Link to Login Screen btnLinkToLogin.setOnClickListener(new View.OnClickListener() { public void onClick(View view) { Intent i = new Intent(getApplicationContext(), LoginActivity.class); startActivity(i); // Close Registration View finish(); } }); } }

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  • Simple way to repeat a String in java

    - by e5
    I'm looking for a simple commons method or operator that allows me to repeat some String n times. I know I could write this using a for loop, but I wish to avoid for loops whenever necessary and a simple direct method should exist somewhere. String str = "abc"; String repeated = str.repeat(3); repeated.equals("abcabcabc"); Related to: repeat string javascript Create NSString by repeating another string a given number of times Edited I try to avoid for loops when they are not completely necessary because: They add to the number of lines of code even if they are tucked away in another function. Someone reading my code has to figure out what I am doing in that for loop. Even if it is commented and has meaningful variables names, they still have to make sure it is not doing anything "clever". Programmers love to put clever things in for loops, even if I write it to "only do what it is intended to do", that does not preclude someone coming along and adding some additional clever "fix". They are very often easy to get wrong. For loops that involving indexes tend to generate off by one bugs. For loops often reuse the same variables, increasing the chance of really hard to find scoping bugs. For loops increase the number of places a bug hunter has to look.

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  • Adding look and feel into java application

    - by Samurai
    I am working with NetBeans 6.5 IDE and i have downloaded a look and feel jar file. I added that to NetBeans by palette manager but i don't know how to use it to my application using code. Anybody please tell me that how to add look and feel into my application? Thanks..

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  • N-tier architecture and unit tests (using Java)

    - by Alexandre FILLATRE
    Hi there, I'd like to have your expert explanations about an architectural question. Imagine a Spring MVC webapp, with validation API (JSR 303). So for a request, I have a controller that handles the request, then passes it to the service layer, which passes to the DAO one. Here's my question. At which layer should the validation occur, and how ? My though is that the controller has to handle basic validation (are mandatory fields empty ? Is the field length ok ? etc.). Then the service layer can do some tricker stuff, that involve other objets. The DAO does no validation at all. BUT, if I want to implement some unit testing (i.e. test layers below service, not the controllers), I'll end up with unexpected behavior because some validations should have been done in the Controller layer. As we don't use it for unit testing, there is a problem. What is the best way to deal with this ? I know there is no universal answer, but your personal experience is very welcomed. Thanks a lot. Regards.

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  • Static variables in Java for a test oObject creator

    - by stevebot
    Hey, I have something like the following TestObjectCreator{ private static Person person; private static Company company; static { person = new Person() person.setName("Joe"); company = new Company(); company.setName("Apple"); } public Person createTestPerson(){ return person; } public Person createTestCompany(){ return company; } } By applying static{} what am I gaining? I assume the objects are singletons as a result. However, if I did the following: Person person = TestObjectCreator.createTestPerson(); person.setName("Jill"); Person person2 = TestObjectCreator.createTestPerson(); would person2 be named Jill or Joe?

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  • What is the best way to transmit Java objects over a network

    - by tomdee
    I am trying to transmit objects of a particular class from one server to another. The options I'm looking at are: Serialize the data as JSON and send it over the wire using HTTP, and de-serialize at the other end. Serialize the data into some binary form and transmit using TCP sockets. What are the best practices in this area? What are the gotchas? Ideally I would like the interface to be versioned, so the sender and receiver can be upgraded independently. I'm considering the JSON approach as I already have code that will serialize/deserialize the objects into JSON.

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  • Write wave files to memory in Java

    - by Cliff
    I'm trying to figure out why my servlet code creates wave files with improper headers. I use: AudioSystem.write( new AudioInputStream( new ByteArrayInputStream(memoryBytes), new AudioFormat(22000, 16, 1, true,false), memoryBytes.length ), AudioFileFormat.Type.WAVE, servletOutputStream ); taking a byte array from memory containing raw PCM samples and a servlet output stream that gets returned to the client. In the result I get a normal wave file but with zeros in the chunk size fields. Is the API broken? I would think that the size could be filled in using the size passed in the audio input stream. But now, after typing this out I'm thinking its not making this info available to the outer write() method on AudioSystem. It seems like the AudioSystem.write call needs a size parameter unless it is able to pull the size from the stream... which wouldn't work with an arbitrary sized stream. Does anyone know how to make this example work?

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  • Parsing JSON to XML using net.sf.json (java)

    - by Castanho
    Hi guys, I'm parsing a generic JSON to a XML using net.sf.json. (I'm not using POJO Obj in the conversion) When dealing with vectors I'm receiving: <root> <entry> <Id>1</accountId> <Items> <e> <cost>0.1</cost> <debit>0.1</debit> </e> <e> <cost>0.1</cost> <debit>0.1</debit> </e> </Items> </entry> </root> When the correct for my point of view should be: <root> <entry> <accountId>1</accountId> <Items> <cost>0.1</cost> <debit>0.1</debit> </Items> <Items> <cost>0.2</cost> <debit>0.2</debit> </Items> </entry> </root> Do anyone have used this lib and could help me? Any tips could help! Thanks in advance

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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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