Am trying to save some field from my jFrame form but when i click the save button, i get the null pointer exception. Previously i was getting the errors that text field couldn't be null so i unchecked not null but it didn't work , i decided not to include Voucher_no in MySQL insert statement as it is an auto increment and its text field is not editable
Is there any problem with my code?
Am Using Mysql Workbench.
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/canning?zeroDateTimeBehavior=convertToNull", "root", "");
con.setAutoCommit(false);
try {
// String kb = jTextField3.getText(); //voucher_no
String kc = (String) jComboBox3.getSelectedItem(); //factory
String kg = jTextField10.getText(); //fuel
Double ks = Double.valueOf(kg);
String ke = jTextField11.getText(); //electricity
Double kt = Double.valueOf(ke);
String kf = jTextField12.getText(); //manpower
Double ku = Double.valueOf(kf);
String kj = (String) jComboBox4.getSelectedItem(); //can_name
String kk = (String) jComboBox5.getSelectedItem(); //label name
String kq = jTextField23.getText();//no_of_cans
Double kv = Double.valueOf(kq);
String kr = jTextField24.getText();//no_of_labels
Double kw = Double.valueOf(kr);
String query1= "insert into production (date,factory,fuel,electricity,manpower,can_name,label_name,no_of_cans,no_of_labels)"
+ "values (?,?,?,?,?,?,?,?,?)";
try (PreparedStatement pst = con.prepareStatement(query1)){
// pst.setString(10, kb);
pst.setString(1, ((JTextField) jDate1.getDateEditor().getUiComponent()).getText());
pst.setString(2, kc);
pst.setDouble(3, ks);
pst.setDouble(4, kt);
pst.setDouble(5, ku);
pst.setString(6, kj);
pst.setString(7, kk);
pst.setDouble(8, kv);
pst.setDouble(9, kw);
pst.execute();
}
try {
int rows = jTable2.getRowCount();
for (int row = 0; row < rows; row++) {
String kd = (String) jTable2.getValueAt(row, 0);
Double kn = (Double) jTable2.getValueAt(row, 1);
try {
// Class.forName("com.mysql.jdbc.Driver").newInstance();
// Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/canning?zeroDateTimeBehavior=convertToNull", "root", "");
String query = "insert into production(product_name,product_quantity)"
+ "values (?,?)";
PreparedStatement update = con.prepareStatement(query);
update.setString(1, kd);
update.setDouble(2, kn);
update.addBatch();
update.executeBatch();
con.commit();
} catch (SQLException e) {
e.printStackTrace();
// JOptionPane.showMessageDialog(this, "Error in production Table");
}
}
} catch (Exception e) {
JOptionPane.showMessageDialog(this, "Invalid Entry in fields");
}
} catch (Exception e) {
e.printStackTrace();
// JOptionPane.showMessageDialog(null, "Invalid in fields");
}
} catch (Exception e) {
e.printStackTrace();
}
The code is doing
update.addBatch();
update.executeBatch();
con.commit();
executeBatch and commit must be done outside the loop.
The misunderstanding arises from "addBatch" that should have been named "addToBatch."
Try doing it this way. First create a connection class as follows;
import java.sql.Connection;
import java.sql.DriverManager;
public class db_connection
{
public Connection connection()
throws Exception
{
try
{
Connection conn = null;
String username = "root"; String password = "";
String driver = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://localhost:3306/database";
try {
Class.forName(driver);
} catch (Exception e) {
e.printStackTrace();
return null;
}
conn = DriverManager.getConnection(url, username, password);
conn.setAutoCommit(false);
return conn;
} catch (Exception e) {
e.printStackTrace();
System.exit(0);
}return null;
}
}
Then on your save button do something like this,
private void ButtonRegGroup_SubmitActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
if ((this.jTextFieldGrp_ReqAmnt.getText().equals(""))
|| (this.jTextFieldGrp_name.getText().equals(""))
|| (this.jTextFieldGrp_Id.getText().equals(""))
|| (this.jTextFieldGrp_prj_name.getText().equals(""))) {
JOptionPane.showMessageDialog(this, "Some fields are empty", this.title, this.error);
} else {
try {
this.con = ((Connection) new db_connection().connection());
this.pst = ((PreparedStatement) this.con.prepareStatement("insert into registered_projects(project_type,name,project_name,project_id,constituency,ward,requested_amount)values(?,?,?,?,?,?,?)"));
GroupRegDetails();
this.pst.setString(1, this.proj_type);
this.pst.setString(2, this.group_name);
this.pst.setString(3, this.proj_name);
this.pst.setInt(4, this.proj_id);
this.pst.setString(5, this.constituency);
this.pst.setString(6, this.ward);
this.pst.setInt(7, this.requested_amount);
int row = this.pst.executeUpdate();
con.commit();
if (row == 0) {
this.con.rollback();
JOptionPane.showInternalMessageDialog(this, "Didn't Register project", this.title, this.error);
}
JOptionPane.showMessageDialog(this, "Project Successfully Registered", this.title, this.infor);
} catch (Exception e) {
e.printStackTrace();
}
}
}
public void GroupRegDetails() {
this.group_name = this.jTextFieldGrp_name.getText();
this.proj_id = Integer.parseInt(this.jTextFieldGrp_Id.getText());
this.proj_name = this.jTextFieldGrp_prj_name.getText();
this.constituency = this.jComboBoxGrp_Comb_const.getSelectedItem().toString();
this.ward = this.jComboBoxGrp_comb_Ward.getSelectedItem().toString();
this.requested_amount = Integer.parseInt(this.jTextFieldGrp_ReqAmnt.getText());
this.proj_type = "Group";
}
And finally good practice is to put fields on a Jpanel and the Jpanel on a Jframe. Hope this helps.
Related
Problem is the following: I am saving hashed password for a school project, however i am stuck on the syntax for the SQL statement to replace the data if it is already present. The table will only need to store a single username/password combination.
public class DatabaseManager {
String dbPath = "jdbc:sqlite:test.db";
public DatabaseManager () {
try {
Class.forName("org.sqlite.JDBC");
Connection conn = DriverManager.getConnection(dbPath);
if (conn != null) {
System.out.println("Connected to the database");
DatabaseMetaData dm = (DatabaseMetaData) conn.getMetaData();
// Setting up database
databaseSetup(conn);
boolean tempInsertion = databaseInsert("pancake", "house", conn);
// Inserting data
if (tempInsertion) {
System.out.println("Data insertion failed");
}
// Retrieving data
List<String> retrievedData = databaseSelect(conn);
if (retrievedData == null) {
System.out.println("Data extraction failed");
}
else {
System.out.println(retrievedData.size());
}
conn.close();
}
}
catch (ClassNotFoundException ex) {
ex.printStackTrace();
} catch (SQLException ex) {
ex.printStackTrace();
}
}
private boolean databaseInsert(String username, String password, Connection conn) {
String sqlInsert = "INSERT OR REPLACE INTO login(username, password) VALUES(?,?)";
PreparedStatement prepStatement;
try {
prepStatement = conn.prepareStatement(sqlInsert);
prepStatement.setString(1, encrypt(username));
prepStatement.setString(2, encrypt(password));
prepStatement.executeUpdate();
} catch (SQLException e) {
return false;
}
return true;
}
private List<String> databaseSelect(Connection conn) {
List<String> tempList = new ArrayList<String>();
String sqlSelect = "SELECT * FROM login";
Statement stmt;
try {
stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(sqlSelect);
tempList.add(rs.getString("username"));
tempList.add(rs.getString("password"));
int columnsNumber = rs.getMetaData().getColumnCount();
while (rs.next()) {
for (int i = 1; i <= columnsNumber; i++) {
if (i > 1) System.out.print(", ");
String columnValue = rs.getString(i);
System.out.print(columnValue + " " + rs.getMetaData().getColumnName(i));
}
System.out.println("");
}
} catch (SQLException e) {
return null;
}
return tempList;
}
private void databaseSetup( Connection conn) {
String sqlExpression = "CREATE TABLE login (username varchar(255), password varchar(255))";
try {
Statement statement = conn.createStatement();
statement.execute(sqlExpression);
} catch (SQLException e) {}
}
private String encrypt(String string) {
try {
MessageDigest exampleCrypt = MessageDigest.getInstance("SHA1");
exampleCrypt.reset();
exampleCrypt.update(string.getBytes("UTF-8"));
return convertByte(exampleCrypt.digest());
}
catch(NoSuchAlgorithmException e) {
System.out.println("Error, cannot encrypt string");
e.printStackTrace();
}
catch(UnsupportedEncodingException e) {
System.out.println("Error, cannot encrypt string");
e.printStackTrace();
}
return null;
}
private static String convertByte(final byte[] hash) {
Formatter formatter1 = new Formatter();
for (byte i : hash) {
formatter1.format("%02x", i);
}
String encryptedData = formatter1.toString();
formatter1.close();
return encryptedData;
}
}
The problem as stated, is that i'd like to only store a single password/username combination at a time, as a hash. However, when this happens it duplicates the hash combination, instead of replacing it.
In my SQL database single record consists of four rows: id, name, age and email. How to get a single record by typing in a JTextField id of that record? So later we can for example System.out.printIn(); it? I know that my question might be stupid for someone who is an SQL expert but I am only a beginner and after searching for this information in the tutorials I could not find it:(. Please help. Here is some of my source code:
public static Connection getConnection() throws Exception{
try{
String driver = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://some IP address/testdb";
String username = "some username";
String password = "some password";
Class.forName(driver);
Connection conn = DriverManager.getConnection(url,username,password);
System.out.println("Connected");
return conn;
} catch(Exception e){System.out.println(e);}
return null;
}
public EsquelTest() {
IDname = new JTextField("");
submit = new JButton("go");
add(IDname);
add(submit);
submit.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(e.getSource() == submit) {
id = IDname.getText().toString();
try {
getConnection();
get(id);
} catch (Exception e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
});
setLayout(new GridLayout());
}
public static ArrayList<String> get(String idname) throws Exception{
try{
Connection con = getConnection();
PreparedStatement statement = con.prepareStatement("Statement needed to get the whole record by owning only an ID");
ResultSet result = statement.executeQuery();
ArrayList<String> array = new ArrayList<String>();
while(result.next()){
array.add(result.getString("last"));
}
System.out.println("All records have been selected!");
return array;
}catch(Exception e){System.out.println(e);}
return null;
}
If you are asking for only SQL statement it is: select * from yourtable where id = theIdThatIsfromTextFieldHere
Yet, if you simply google it you will find thousands of answers. here for instance.
The SQL Statement would be SELECT * FROM yourtable WHERE id = yourid. So to embed it into your code it would look something like this:
public static Connection getConnection() throws Exception{
try{
String driver = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://some IP address/testdb";
String username = "some username";
String password = "some password";
Class.forName(driver);
Connection conn = DriverManager.getConnection(url,username,password);
System.out.println("Connected");
return conn;
} catch(Exception e){System.out.println(e);}
return null;
}
public EsquelTest() {
IDname = new JTextField("");
submit = new JButton("go");
add(IDname);
add(submit);
submit.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(e.getSource() == submit) {
id = IDname.getText().toString();
try {
getConnection();
get(id);
} catch (Exception e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
});
setLayout(new GridLayout());
}
public static ArrayList<String> get(String idname) throws Exception{
try{
Connection con = getConnection();
PreparedStatement statement = con.prepareStatement("SELECT * FROM {REPLACE WITH YOUR TABLE} WHERE id = "+idname);
ResultSet result = statement.executeQuery();
ArrayList<String> array = new ArrayList<String>();
while(result.next()){
array.add(result.getString("last"));
}
System.out.println("All records have been selected!");
return array;
}catch(Exception e){System.out.println(e);}
return null;
}
Just a Tip: Don't name you function "get" as this is a commonly used keyword in other programming languages that only causes confusion.
Try it:
public static Connection getConnection() throws Exception{
try{
String driver = "com.mysql.jdbc.Driver";
String url = "jdbc:mysql://some IP address/testdb";
String username = "some username";
String password = "some password";
Class.forName(driver);
Connection conn = DriverManager.getConnection(url,username,password);
System.out.println("Connected");
return conn;
} catch(Exception e){System.out.println(e);}
return null;
}
public EsquelTest() {
IDname = new JTextField("");
submit = new JButton("go");
add(IDname);
add(submit);
submit.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if(e.getSource() == submit) {
id = IDname.getText().toString();
try {
getConnection();
for(String string:get(id)){
System.out.println(string);
}
// get(id);
} catch (Exception e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
});
setLayout(new GridLayout());
}
public static ArrayList<String> get(String idname) throws Exception{
try{
Connection con = getConnection();
// You should replace "YourTableName" With table in databace that you work with it
PreparedStatement statement = con.prepareStatement("SELECT * FROM YourTableName WHERE id = '" + idName+"'");
//If type of your id in database is Int write this code :
// int id= Integer.parseInt(idName);
//PreparedStatement statement = con.prepareStatement("SELECT * FROM YourTableName WHERE id = " + idName);
ResultSet result = statement.executeQuery();
ArrayList<String> array = new ArrayList<String>();
result.next();
//This array has all data in single recorde
array.add(result.getString("id"));
array.add(result.getString("name"));
array.add(result.getString("age"));
array.add(result.getString("email"));
// I removed this rows becuse you have only one record
// while(result.next()){
//
// array.add(result.getString("last"));
// }
System.out.println("All records have been selected!");
return array;
}catch(Exception e){System.out.println(e);}
return null;
}
I have a bit of a problem with inserting some data in the database. The data is being read by an CSV parser and changed to data besides that, I continue to get this error message:
Connected to the PostgreSQL server successfully.
Naam van de garage: P_Erasmusbrug, Longditude: 4.482313155, Latitude: 51.91024645
org.postgresql.util.PSQLException: The column index is out of range: 1, number of columns: 0.
at org.postgresql.core.v3.SimpleParameterList.bind(SimpleParameterList.java:65)
at org.postgresql.core.v3.SimpleParameterList.setStringParameter(SimpleParameterList.java:128)
at org.postgresql.jdbc.PgPreparedStatement.bindString(PgPreparedStatement.java:1023)
at org.postgresql.jdbc.PgPreparedStatement.setString(PgPreparedStatement.java:374)
at org.postgresql.jdbc.PgPreparedStatement.setString(PgPreparedStatement.java:358)
at Database.ConnectDatabase.parser(ConnectDatabase.java:80)
at Events.CSVReader.main(CSVReader.java:40)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)
Thank you for your service.
Naam van de garage: P_St.Jacobsplaats, Longditude: 4.482054381, Latitude: 51.92410235
Thank you for your service.
Naam van de garage: P_Schouwburgplein, Longditude: 4.473618335, Latitude: 51.92102728
org.postgresql.util.PSQLException: The column index is out of range: 1, number of columns: 0.
Which continues for all the other lines of data. Is there maybe a way to fix this as I don't really understand what the error message includes..
The a, b2, and c2 are variables for the ''name'' , ''londitude'' and ''latitude''.
package Database;
import java.io.*;
import java.sql.*;
import java.util.HashMap;
import java.sql.SQLException;
public class ConnectDatabase {
private final String url = "jdbc:postgresql://localhost/Project3";
private final String user = "postgres";
private final String password = "kaas123";
private Connection conn;
public Connection connect() {
Connection conn = null;
try {
conn = DriverManager.getConnection(url, user, password);
System.out.println("Connected to the PostgreSQL server successfully.");
} catch (SQLException exception) {
System.out.println(exception.getMessage());
}
this.conn = conn;
return conn;
}
public HashMap getGarages() {
HashMap<String, Double> newHashMap = new HashMap<String, Double>();
try {
Statement stmt = conn.createStatement();
ResultSet rs;
rs = stmt.executeQuery("SELECT deelgemeente, COUNT(garagenaam) FROM garages GROUP BY deelgemeente");
while (rs.next()) {
String deelGemeenteNaam = rs.getString("deelgemeente");
double garageNaamCount = rs.getDouble("COUNT");
newHashMap.put(deelGemeenteNaam, garageNaamCount);
}
} catch (Exception e) {
System.err.println("Got an exception!");
System.err.println(e.getMessage());
}
return newHashMap;
}
public HashMap getTheftYear(int year) {
HashMap<String, Double> newHashMap = new HashMap<String, Double>();
try {
Statement stmt = conn.createStatement();
ResultSet rs;
rs = stmt.executeQuery("SELECT deelgemeente, percentagediefstal FROM autodiefstal WHERE jaar = " + year);
while (rs.next()) {
String deelGemeenteNaam = rs.getString("deelgemeente");
double deelPercentage = rs.getDouble("percentagediefstal");
newHashMap.put(deelGemeenteNaam, deelPercentage);
}
} catch (Exception e) {
System.err.println("Got an exception!");
System.err.println(e.getMessage());
}
return newHashMap;
}
public int parser(String a, float b2, float c2) {
int updated = 0;
Connection conn = null;
PreparedStatement stmt = null;
try {
conn = DriverManager.getConnection(url, user, password);
String insertSQL = "INSERT INTO testparser(garagenaam, xpos, ypos) VALUES(" + a + "," + b2 + "," + c2 + ")";
stmt = conn.prepareStatement(insertSQL);
stmt.setString(1, a);
stmt.setFloat(2, b2);
stmt.setFloat(3, c2);
System.out.println("Inserted data into the database...");
updated = stmt.executeUpdate();
} catch (SQLException se) {
se.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (stmt != null)
conn.close();
} catch (SQLException se) {
}
try {
if (conn != null)
conn.close();
} catch (SQLException se) {
se.printStackTrace();
}
}
System.out.println("Thank you for your service.");
this.conn = conn;
return updated;
}
}
You aren't correctly using the ? placeholders system, replace :
String insertSQL = "INSERT INTO testparser(garagenaam, xpos, ypos) VALUES(" + a + "," + b2 + "," + c2 + ")";
with
String insertSQL = "INSERT INTO testparser(garagenaam, xpos, ypos) VALUES(?,?,?)";
I am trying to write a runnable jar file that can be able to connect to 2 different databases informix old database and oracle new database. It should be able to update the new database(oracle) with the old database(informix) records.
I re-edit my java code I added separate methods for my select, update and connections I am not getting an error but its not updating my db. My select works but my update statement is not working. This is my result i get - SELECT profile_id, ingress_flag, egress_flag, ce_ingress_flag, ce_egress_flag from COS_PROFILE where profile_id = 102
profileid : 102
ingressflag : Y
egress_flag : Y
ceingressflag : Y
ceegressflag : Y
ResultSet not open, operation 'next' not permitted. Verify that autocommit is OFF
I am not sure how can I fixed the ResultSet not open, operation 'next' not permitted. Verify that autocommit is OFF
public class TestConnection {
static ResultSet rs;
public static void main (String[] args) throws Exception {
try{
selectRecordsIcore();
updateRecordIntoBids();
} catch (SQLException e) {
System.out.println(e.getMessage());
}
}
public static void selectRecordsIcore() throws SQLException {
Connection dbConnection = null;
Statement statement = null;
String selectTableSQL = "SELECT profile_id, ingress_flag, egress_flag, ce_ingress_flag, ce_egress_flag from COS_PROFILE";
try {
dbConnection = getInformixConnection();
statement = dbConnection.createStatement();
System.out.println(selectTableSQL);
// execute select SQL stetement
rs = statement.executeQuery(selectTableSQL);
while (rs.next()) {
int profileid = rs.getInt("profile_id");
String ingressflag = rs.getString("ingress_flag");
String egress_flag = rs.getString("egress_flag");
String ceingressflag = rs.getString("ce_ingress_flag");
String ceegressflag = rs.getString("ce_egress_flag");
System.out.println("profileid : " + profileid);
System.out.println("ingressflag : " + ingressflag);
System.out.println("egress_flag : " + egress_flag);
System.out.println("ceingressflag : " + ceingressflag);
System.out.println("ceegressflag : " + ceegressflag);
}
} catch (SQLException e) {
System.out.println(e.getMessage());
} finally {
if (statement != null) {
statement.close();
}
if (dbConnection != null) {
dbConnection.close();
}
}
}
private static void updateRecordIntoBids() throws SQLException {
Connection dbConnection = null;
Statement statement = null;
ArrayList<TempStorageRecords> updateSQL = new ArrayList<TempStorageRecords>();
while (rs.next()) {
int profileid = rs.getInt("profile_id");
String ingressflag = rs.getString("ingress_flag");
String egress_flag = rs.getString("egress_flag");
String ceingressflag = rs.getString("ce_ingress_flag");
String ceegressflag = rs.getString("ce_egress_flag");
String updateTableSQL = "UPDATE traffic_profile SET ingress_flag = " + ingressflag
+ " ,egress_flag = " + egress_flag
+ " ,ce_ingress_flag = " + ceingressflag
+ " ,ce_egress_flag = " + ceegressflag
+ " WHERE profile_id = " + profileid + ";";
try {
dbConnection = getOracleConnection();
statement = dbConnection.createStatement();
System.out.println("updateTableSQL 1 :" + updateTableSQL);
// execute update SQL stetement
statement.execute(updateTableSQL);
System.out.println("updateTableSQL 2: " + updateTableSQL);
} catch (SQLException e) {
System.out.println(e.getMessage());
} finally {
if (statement != null) {
statement.close();
}
if (dbConnection != null) {
dbConnection.close();
}
}
}
}
public static Connection getOracleConnection() throws SQLException {
String driver = "oracle.jdbc.driver.OracleDriver";
String url = "jdbc:oracle:thin:#oracle_host:1521:BIDS";
String username = "username";
String password = "password";
try {
Class.forName(driver);
} catch (ClassNotFoundException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} // load Oracle driver
Connection dbConnection = null;
try {
Class.forName(driver);
} catch (ClassNotFoundException e) {
System.out.println(e.getMessage());
}
try {
dbConnection = DriverManager.getConnection(
url, username,password);
return dbConnection;
} catch (SQLException e) {
System.out.println(e.getMessage());
}
return dbConnection;
}
public static Connection getInformixConnection() throws SQLException {
String driver = "com.informix.jdbc.IfxDriver";
String url = "jdbc:informix-sqli://informix_host:1615/icore:INFORMIXSERVER=icit";
String username = "user";
String password = "pass";
try {
Class.forName(driver);
} catch (ClassNotFoundException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} // load Informix driver
Connection dbConnection = null;
try {
Class.forName(driver);
} catch (ClassNotFoundException e) {
System.out.println(e.getMessage());
}
try {
dbConnection = DriverManager.getConnection(
url, username,password);
return dbConnection;
} catch (SQLException e) {
System.out.println(e.getMessage());
}
return dbConnection;
}
}
At first try to export data from source database into text file.
Your code uses hard coded column names, but I think it could read table names to export from some config file and column names from metadata from SELECT * FROM [table_name]. In JDBC there is getMetaData() for RecordSet. Use it.
When you export data into text files without problems you can do the next step: import such data directly from the source database to the destination database.
For destination database create prepareStatement with:
'INSERT INTO ' + table_name_dest + ' (' + column_names +') VALUES ('+ question_marks + ')'
(there question_marks are '?' chars which maps to columns).
Then for each record from source table and for each record (row) do:
insert_stmt.setObject(i, rs_in.getObject(i))
For big tables you can also use setFetchSize() and addBatch()/executeBatch()
public class Model
{
public static Connection getConnection()
{
Connection conn = null;
try
{
Class.forName("oracle.jdbc.OracleDriver");
conn = DriverManager.getConnection("jdbc:oracle:thin:#localhost:1521:xe", "System", "system");
}
catch(ClassNotFoundException e)
{
e.printStackTrace();
}
catch(SQLException e)
{
e.printStackTrace();
}
return conn;
}
public static class Cart
{
public String itmName="";
public int howmany=0;
public static long itmQty=0, itmID=0;
public double itmPrice=0.0, itmCost=0.0, totalSum=0.0;
}
public static ArrayList<Cart> getCartDatabase(String user) throws Exception
{
Connection conn = getConnection();
String sql = "select * from userCarts where userID = '" + user + "'";
PreparedStatement pstmt = conn.prepareStatement(sql);
ResultSet rst = pstmt.executeQuery();
ArrayList<Cart> al = null;
Cart crt=null;
while(rst.next())
{
System.out.println("CPoint");
try
{
long p = rst.getLong("itemID");
crt.itmID = p; // This is the line thats creating the error
System.out.println(p + " is long! I guess...");
}
catch(NullPointerException e)
{
System.out.println("NPE Caught in Model");
}
System.out.println("CP 1 " + crt.itmID);
ArrayList<row> alr=null;
try
{
alr = Model.getStoreInventory();
}
catch(Exception e)
{
e.printStackTrace();
}
System.out.println("CP 2");
for(int i=0; i<alr.size(); i++)
{
crt.itmName = alr.get(i).itmName;
crt.itmPrice = alr.get(i).itmPrice;
crt.itmQty = alr.get(i).itmQty;
}
System.out.println("CP 3");
crt.howmany = rst.getInt("howmany");
crt.itmCost = crt.itmPrice*crt.howmany;
al.add(crt);
}
return al;
}
}
When I try to access this method of getCartFromDatabase, it gives a NullPointerException however I don't understand why it would do this. Moreover, I tried to make the class as a non static class too, but still it gave the same error:
"Possible deferencing Null Pointer"
Cart crt=null;
while(rst.next())
{
System.out.println("CPoint");
try
{
long p = rst.getLong("itemID");
crt.itmID = p; // This is the line thats creating the error
System.out.println(p + " is long! I guess...");
}
crt is null when you try to access crt.itemID. You have to assign it an instance first.
I think you may simply change the first line from the snippet to
Cart crt = new Cart();