Error Handling Query Java.lang.nullpointerexception Null
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Java.lang.nullpointerexception In Java
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Null Pointer Exception
of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up (SOLVED) java.lang.NullPointerException … Initializing the JDBC MYSQL connection up vote -1 down vote favorite I've already gone through several threads but haven't got any solution yet. Please don't suggest me to use InternalFrame or Dialogs. I can't start the project from beginning. Theme: I'm building a GUI program to display mark-sheet. I've taken 3 JFrames & 1 simple class... Frame1.java It's having 1 JTextField to enter roll_no. & 2 buttons to feedData in DB & showResult. feedData button calls Frame2 & showResult button calls Frame3. Frame2.java For feeding data have several JTextFields & Buttons that transfer content to mySQL DB. Frame3.java is a result window that fetches content from DB. Support.java Contains static variables & getter-setter methods for them ..... .....//contains in Support.java public boolean add() { query = "Insert into table1 (enroll,Sname,Fname,sub1,sub2,sub3,sub4,sub5 )values(?,?,?,?,?)"; try { PreparedStatement psmt = conn.prepareStatement(query); psmt.setString(1, enroll); psmt.setString(2, Sname); psmt.setString(3, Fname); psmt.setInt(4, sub1); psmt.setInt(5, sub2); psmt.setInt(6, sub3); psmt.setInt(7, sub4); psmt.setInt(8, sub5); int y = 0; y = psmt.executeUpdate(); if (y == 0) { return false; } } catch (Exception e) { e.printStackTrace(); return false; } return true; } add() is called on pressing save button in Frame2.java . . . If catch block is executing, why println(query) printing NULL java mysql swing share|improve this question edited May 17 '14 at 10:03 asked Jan 27 '14 at 18:47 Adarsh Singhal 111110 What exception are you getting? I'm guessing it's failing trying to create the statement. –evanchooly Jan 27 '14 at 18:49 2 Side note: Use PreparedStatements, your code is vulnerable to SQL injections –BackSlash Jan 27 '14 at 18:49 If I had to guess, I'd say your problem is that you haven't initialized conn. –Ian McLaird Jan 27 '14 at 19:09 I guess, Ian McLaird... You're talking about conn = DriverManager.getConnec
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up java.lang.NullPointerException error on a query up vote http://stackoverflow.com/questions/21389079/solved-java-lang-nullpointerexception-initializing-the-jdbc-mysql-connecti 3 down vote favorite i'm ready to develop my second app for android, and I want to use the database. But I'm blocked by an error. This is the class: public class MyDatabase { SQLiteDatabase mDb; DbHelper mDbHelper; Context mContext; private static final String DB_NAME="epsoftsms";//nome del db private static final int DB_VERSION=1; //numero di versione del nostro db public MyDatabase(Context ctx){ mContext=ctx; mDbHelper=new DbHelper(ctx, DB_NAME, null, http://stackoverflow.com/questions/10948678/java-lang-nullpointerexception-error-on-a-query DB_VERSION); //quando istanziamo questa classe, istanziamo anche l'helper (vedi sotto) } public void open(){ //il database su cui agiamo รจ leggibile/scrivibile mDb=mDbHelper.getWritableDatabase(); } public void close(){ //chiudiamo il database su cui agiamo mDb.close(); } //i seguenti 2 metodi servono per la lettura/scrittura del db. aggiungete e modificate a discrezione // consiglio:si potrebbe creare una classe Prodotto, i quali oggetti verrebbero passati come parametri dei seguenti metodi, rispettivamente ritornati. Lacio a voi il divertimento public void inserimentoParametri(String parametro,String valore){ //metodo per inserire i dati ContentValues cv=new ContentValues(); cv.put(ParametriMetaData.PARAMETRO, parametro); cv.put(ParametriMetaData.VALORE, valore); mDb.insert(ParametriMetaData.TAB_PARAMETRI, null, cv); } public Cursor listaParametri(){ //metodo per fare la query di tutti i dati return mDb.query(ParametriMetaData.TAB_PARAMETRI, null,null,null,null,null,null); } static class ParametriMetaData { // i metadati della tabella, accessibili ovunque static final String TAB_PARAMETRI = "parametri"; static final String PARAMETRO = "_parametro"; static final String VALORE = "valore"; } private static final String CREA_TAB_PARAMETRI = "CREATE TABLE IF NOT EXISTS " //codice sql di creazione della tabella + ParametriMetaData.TAB_PARAMETRI + " (" + ParametriMetaData.PARAMETRO+ " text primary key, " + ParametriMetaData.VALORE + " text not null);"; private class DbHelper extends SQLiteOpenHelper { //classe che ci aiuta nella creazione del db public DbHelper(Context context, String name, CursorFactory factory,i
Common cause of NullPointerException in Java Example java.lang.NullPointerException or NullPointerException in Java is probably the first Exception you will face in Java. It is true nightmare for beginners in Java but pretty easy to solve once you get familiar with Exception handling in Java. What makes NullPointerException little tricky is its name which has pointer in itself and Java does not support pointers like multiple inheritance in Java . In this article we will see What is NullPointerException in Java, How to solve Exception in thread "main" java.lang.NullPointerException, finding possible cause of Java NullPointerException and how to troubleshoot NPE in Java. Based on my experience once you know little bit about NullPointerException its pretty easy to solve. By the way, as said, "prevention is better than cure", you can avoid != null check and NullPointerException by following some best practices. What is NullPointerException in Java NullPointerException in Java is nothing but an error or precisely an exception which occurs if we tried to perform any operation on object which is null. In Java reference variable points to object created in heap but when you create a reference variable of type object by default its point to "null" and when you try to call any method on null, try to access any variable on null you will get this null pointer exception. no matter by what reason your reference variable is pointing to null be it not initialized or set to null if you perform any operation it will throw Exception in thread main : java.lang.NullPointerException When does NullPointerException occurs in Java Javadoc of java.lang.NullPointerException has outlined scenario when it could be occurred: 1) When you call instance method on a null object. you won't get null pointer exception if you call static method or class method on null object because static method doesn't require an instance to call any method. 2) While accessing or changing any variable or field on