احمد صوالحة

يظهر لي الخطأ التالي عند تشغيل برنامج جافا: Java Runtime (class file version 53.0), this version of the Java Runtime only recognizes class file versions up to 52.0 مع انني استخدم احدث اصدار للـJDK ولدي القيمة JAVA_HOME : C:\Program Files\Java\jdk-15.0.2 في Environment Variables. ما هو الـclass file version وكيف أحل هذه المشكلة ؟

سبب المشكلة هو السطر التالي في كود الـfragment: recyclerView = container.findViewById(R.id.recycleViewHome); لحل المشكلة يجب تعديل السطر ليصبح هكذا: recyclerView = view.findViewById(R.id.recycleViewHome); أي أننا إستخدما view بدلاً من container لجلب الـrecyclerView الخاص بنا.

يحدث لدي الخطأ التالي: ERROR Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager) ' on a null object reference at com.example.application.Fragments.Home.HomeFragment.onCreate(HomeFragment.java:32) الشاشة الرئيسية: class MainActivity extends AppCompatActivity { private BottomNavigationView bottomNavigationView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); bottomNavigationView = findViewById(R.id.bottonNavigationView); loadFragment(new HomeFragment()); setBottomNavigationView(); } private void loadFragment(Fragment fragment) { FragmentManager fragmentManager = getSupportFragmentManager(); FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction(); fragmentTransaction.replace(R.id.idMainFrameLayout, fragment); fragmentTransaction.commit(); } @SuppressLint("NonConstantResourceId") public void setBottomNavigationView() { bottomNavigationView.setOnNavigationItemSelectedListener(item -> { switch (item.getItemId()) { case R.id.btnSearch: loadFragment(new SearchFragment()); break; case R.id.btnFeed: loadFragment(new FeedFragment()); break; case R.id.btnShedule: loadFragment(new SheduleFragment()); break; case R.id.btnProfile: loadFragment(new ProfileFragment()); break; default: loadFragment(new HomeFragment()); } return true; }); } } كود الfragment: class HomeFragment extends Fragment { private RecyclerView recyclerView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } @Nullable @Override public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { View view = inflater.inflate(R.layout.fragment_home, container, false); recyclerView = container.findViewById(R.id.recycleViewHome); recyclerView.setAdapter(new MyAdapter(getMyList())); recyclerView.setLayoutManager(new LinearLayoutManager(getContext())); return view; } private ArrayList<Store> getMyList() { String mTitle = "Google", mSubTitle = "Description"; int imageView = R.drawable.ic_google_svg; ArrayList<Store> storeArrayList = new ArrayList<>(); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); storeArrayList.add(new Store(imageView, mTitle, mSubTitle)); return storeArrayList; } } واجهة الfragment: <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" xmlns:app="http://schemas.android.com/apk/res-auto" android:orientation="vertical" tools:context=".Fragments.Home.HomeFragment"> <androidx.recyclerview.widget.RecyclerView app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager" android:id="@+id/recycleViewHome" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginStart="20dp" android:layout_marginTop="10dp" android:layout_marginEnd="20dp" android:orientation="vertical" tools:listitem="@layout/card_layout_stores" /> </LinearLayout>

احاول جلب بيانات من الـfirebase لكن يظهر لدي الخطأ التالي: E/AndroidRuntime: FATAL EXCEPTION: main Process: com.luvtas.campingau, PID: 11763 com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.luvtas.campingau.Model.CamperSiteModel at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:436) at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:232) at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80) at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:203) at com.luvtas.campingau.Fragment.ExploreFragment$3.onDataChange(ExploreFragment.java:128) at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75) at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63) at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55) at android.os.Handler.handleCallback(Handler.java:790) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6494) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) هذا هو الكود: private RecyclerView recyclerView; private CamperSiteAdapter camperSiteAdapter; private List<CamperSiteModel> camperSiteModel; EditText seatch_bar; private void readCampSite(){ DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Cte"); reference.addValueEventListener(new ValueEventListener() { @Override public void onDataChange(@NonNull DataSnapshot dataSnapshot) { if(seatch_bar.getText().toString().equals("")){ camperSiteModel.clear(); for(DataSnapshot snapshot : dataSnapshot.getChildren()){ CamperSiteModel camperSiteModel1 = snapshot.getValue(CamperSiteModel.class); camperSiteModel.add(camperSiteModel1); } camperSiteAdapter.notifyDataSetChanged(); } } @Override public void onCancelled(@NonNull DatabaseError error) { } }); } كود الـmodel: public CamperSiteModel() { } public CamperSiteModel(String camperSiteID, String camperSiteName, String camperSiteImage, String camperSiteType, String camperSiteDistance, String camperSiteInfo, String camperSiteSummary, String camperSiteAddress, String camperSiteLatitude, String camperSiteLongitude, String camperSitePrice1, String camperSitePrice2, String camperSiteEmail, String camperSiteSub) { CamperSiteID = camperSiteID; CamperSiteName = camperSiteName; CamperSiteImage = camperSiteImage; CamperSiteType = camperSiteType; CamperSiteDistance = camperSiteDistance; CamperSiteInfo = camperSiteInfo; CamperSiteSummary = camperSiteSummary; CamperSiteAddress = camperSiteAddress; CamperSiteLatitude = camperSiteLatitude; CamperSiteLongitude = camperSiteLongitude; CamperSitePrice1 = camperSitePrice1; CamperSitePrice2 = camperSitePrice2; CamperSiteEmail = camperSiteEmail; CamperSiteSub = camperSiteSub; } فما هي المشكلة ؟

لدي تطبيق يقوم بمحاولة بإنشاء اتصال بقواعد البيانات mysql ويظهر الخطأ التالي: I/System.out: Error ************************java.sql.SQLNonTransientConnectionException: Could not create connection to database server. W/System.err: java.lang.NullPointerException: Attempt to invoke interface method 'java.sql.Statement java.sql.Connection.createStatement()' on a null object reference at com.example.testjdbc.MainActivity.getUserList(MainActivity.java:54) W/System.err: at com.example.testjdbc.MainActivity.showData(MainActivity.java:73) W/System.err: at com.example.testjdbc.MainActivity.onCreate(MainActivity.java:24) at android.app.Activity.performCreate(Activity.java:7136) W/System.err: at android.app.Activity.performCreate(Activity.java:7127) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:193) at android.app.ActivityThread.main(ActivityThread.java:6669) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) الكود: private Connection getConnection(){ Connection con; try{ Class.forName("com.mysql.cj.jdbc.Driver").newInstance(); con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/testandroid?useUnicode=true&characterEncoding=UTF-8&zeroDateTimeBehavior=CONVERT_TO_NULL&serverTimezone=GMT","root",""); return con; }catch (Exception e){ System.out.println("Error :"+e); return null; } } private ArrayList<User> getUserList() { ArrayList<User> userList = new ArrayList<>(); Connection connection = getConnection(); String query = "Select pseudo FROM `users` where userID="+1; Statement st; ResultSet rs; try{ st = connection.createStatement(); rs = st.executeQuery(query); User user ; while (rs.next()) { user = new User(rs.getString("pseudo")); userList.add(user); } }catch (Exception e){ e.printStackTrace(); } return userList; } private void showData(){ ArrayList<User> list = getUserList(); for (int i=0; i<list.size(); i++){ test.setText(list.get(i).getPseudo()); test.setText("gn"); } }

يحدث الخطأ عند إستدعاء الكود التالي: BottomSheetScaffold( scaffoldState = bottomSheetScaffoldState, sheetContent = { Text("anything") }, sheetShape = Shapes.large, backgroundColor = AppTheme.colors.uiBackground, modifier = modifier ) { (content) } رسالة الخطأ: java.lang.IllegalArgumentException: The initial value must have an associated anchor. هل هناك أي إقتراحات لحل المشكلة ؟

لدي تطبيق يقوم بعرض RSS Feed من موقع معين، يظهر لي الخطأ التالي عند تشغيل التطبيق: android.os.NetworkOnMainThreadException هذا هو الكود التي تحصل فيه المشكلة: URL url = new URL(urlToRssFeed); SAXParserFactory factory = SAXParserFactory.newInstance(); SAXParser parser = factory.newSAXParser(); XMLReader xmlreader = parser.getXMLReader(); RssHandler theRSSHandler = new RssHandler(); xmlreader.setContentHandler(theRSSHandler); InputSource is = new InputSource(url.openStream()); xmlreader.parse(is); return theRSSHandler.getFeed();

لدي الكود التالي: public class Main { public static boolean calculateAge(LocalDate date) { LocalDate DateToday = LocalDate.now(); Period period = Period.between(date, DateToday); int age = period.getYears(); if (age>19){ return true; } else{ return false; } } public static void main(String [] args) { Scanner sc = new Scanner(System.in); System.out.println("Enter Date of Birth : dd-mm-yyyy"); String dateEntered = sc.next(); if(Pattern.matches("(0[1-9]|[12][0-9]|3[01])\\-(0[1-9]|[1][12])\\-([12][0-9][0-9][0-9])", dateEntered)){ DateTimeFormatter dtf=DateTimeFormatter.ofPattern("yyyy-mm-dd"); LocalDate localDate= LocalDate.parse(dateEntered, dtf); calculateAge(localDate); } else{ System.out.println("Wrong Date"); } } } يحدث الخطأ التالي عند معالجة التاريخ المدخل من قبل المستخدم: Exception in thread "main" java.time.format.DateTimeParseException: Text '03-09-1999' could not be parsed at index 0 at java.base/java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:2051) at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1953) at java.base/java.time.LocalDate.parse(LocalDate.java:429) at java.base/java.time.LocalDate.parse(LocalDate.java:414) at Main.main(Main.java:26) ما هو سبب ظهور الخطأ ؟

لنتفرض أن لدي الكود التالي: public static void main() { stopCommand(); searchCommand(); } أريد تنفيذ الدالة الأولى في حال تم إرفاق الأمر stop في سطر الأوامر والدالة الثانية في حال تم إرفاق search، كيف أحقق هذه النتيجة ؟

احاول تشغيل الكود من الموقع التالي: https://gitlab.inria.fr/structgraphics/code/ يظهر لي الخطأ التالي: Error: Could not find or load main class Chan\git\code\target\classes;C:\Users\ahmad Caused by: java.lang.ClassNotFoundException: Chan\git\code\target\classes

احاول معالجة كود xml بعد جلبه من موقع معين حيث يحدث الخطأ التالي: [Fatal Error] :1:1: Premature end of file. org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 1; Premature end of file. at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source) هذه هي الجزئية المسؤولة عن قراءة الكود: String eD = IOUtils.toString(request.getReader()); DocumentBuilder db1 = null; try { db1 = DocumentBuilderFactory.newInstance().newDocumentBuilder(); } catch (ParserConfigurationException e) { e.printStackTrace(); } InputSource is = new InputSource(); is.setCharacterStream(new StringReader(eD)); Document doc1 = null; try { doc1 = db1.parse(is); } catch (SAXException e) { e.printStackTrace(); } ما هو سبب المشكلة؟

عند محاولة تشغيل برنامج بصيغة jar عن طريق الأمر التالي : java -jar myApp.jar يظهر الخطأ التالي: no main manifest attribute, in "myApp.jar" ما هي المشكلة ؟

يحدث الخطأ " not a statement " أثناء إستدعاء الدالة التالية: public boolean binarySearch(int[] list, int target, int low, int high) { list ={"1,2,5,7,9,15"}; target = 5; boolean result = binarySearch(list, target, 0, list.length-1); executions++; int mid = (low + high) / 2; if(!result){ System.out.println("Target not found -- bad search."); }else{ System.out.println("Target found -- sucessful search!"); } if (list[mid] == target) { return true; } else { if (low > high) { return false; } else { comparisons++; if (list[mid] < target) { return binarySearch(list, target, mid + 1, high); } else { return binarySearch(list, target, low, mid - 1); } } لم أفهم ماذا تعني رسالة الخطأ ؟ وما هو الحل ؟

لدي برنامج يقوم بقراءة ملف اكسيل ويرفع محتوياته الى قاعدة البيانات وهو يعمل بشكل جيد لكن في حال كانت خلية ما فارغة يظهر لي الخطأ التالي: java.lang.NullPointerException هذا هو الكود الذي يحصل فيه الخطأ: public void upload() throws IOException{ String host="localhost"; String port="543"; String db_name="postgr"; String username="root"; String password="root"; int max = 1000; int min = 0; String dir="C:\\Users\\User\\Desktop\\book.xlsx"; int batchSize = 20; Connection connection = null; try { long start = System.currentTimeMillis(); FileInputStream inputStream = new FileInputStream(dir); Workbook workbook = new XSSFWorkbook(inputStream); Sheet firstSheet = workbook.getSheetAt(0); Iterator<Row> rowIterator = firstSheet.iterator(); try { Class.forName("org.postgresql.Driver"); } catch (ClassNotFoundException e) { e.printStackTrace(); } connection = DriverManager.getConnection("jdbc:postgresql://"+host+":"+port+"/"+db_name+"", ""+username+"", ""+password+""); connection.setAutoCommit(false); String sql = "INSERT INTO survey.tabledata (id,col1,col2,col3,col4,col5,col6,col7,col8,col9,col10,surveyid) VALUES (?,?,?,?,?,?,?,?,?,?,?,?)"; PreparedStatement statement = connection.prepareStatement(sql); int count = 0; while (rowIterator.hasNext()) { Row nextRow = rowIterator.next(); Iterator<Cell> cellIterator = nextRow.cellIterator(); while (cellIterator.hasNext()) { Cell nextCell = cellIterator.next(); int columnIndex = nextCell.getColumnIndex(); switch (columnIndex) { case 0: int col1 = (int) nextCell.getNumericCellValue(); statement.setInt(1,col1); break; case 1: String col2 = nextCell.getStringCellValue(); statement.setString(2, col2); break; case 2: String col3 = nextCell.getStringCellValue(); statement.setString(3, col3); break; case 3: String col4 = nextCell.getStringCellValue(); statement.setString(4, col4); break; case 4: String col5 = nextCell.getStringCellValue(); statement.setString(5, col5); break; case 5: String col6 = nextCell.getStringCellValue(); statement.setString(6, col6); break; case 6: String col7 = nextCell.getStringCellValue(); statement.setString(7, col7); break; case 7: String col8 = nextCell.getStringCellValue(); statement.setString(8, col8); break; case 8: String col9 = nextCell.getStringCellValue(); statement.setString(9, col9); break; case 9: String col10 = nextCell.getStringCellValue(); statement.setString(10, col10); break; case 10: String col11 = nextCell.getStringCellValue(); statement.setString(11, col11); break; case 11: int col12 = (int) nextCell.getNumericCellValue(); statement.setInt(12,col12); break; } } statement.addBatch(); if (count % batchSize == 0) { statement.executeBatch(); } } statement.executeBatch(); connection.commit(); connection.close(); long end = System.currentTimeMillis(); System.out.printf("import done"); } catch (IOException ex1) { System.out.println("Error"); ex1.printStackTrace(); } catch (SQLException ex2) { System.out.println("error"); ex2.printStackTrace(); } } كيف اتخطى تلك المشكلة ؟

عندما أقوم بعمل Junit testing يظهر لي الخطأ التالي: java.lang.OutOfMemoryError ما معنى هذا الخطأ ؟