I'm trying to do an exercise from a java book. The code comes as is and I have not added anything to the code besides setting the path for the database. I'm on OSX, so I had to install Apache Derby. Everytime I build and run the program I get this:
Derby has been started.
Product list:
bvbn Murach's Beginning Visual Basic .NET $49.50
cshp Murach's C# $49.50
java Murach's Beginning Java $49.50
jsps Murach's Java Servlets and JSP $49.50
mcb2 Murach's Mainframe COBOL $59.50
sqls Murach's SQL for SQL Server $49.50
zjcl Murach's OS/390 and z/OS JCL $62.50
Exception in thread "main" java.lang.NullPointerException
First product:
at DBTesterApp.printProduct(DBTesterApp.java:117)
at DBTesterApp.printFirstProduct(DBTesterApp.java:66)
at DBTesterApp.main(DBTesterApp.java:16)
Java Result: 1
BUILD SUCCESSFUL (total time: 2 seconds)
I'm confused as to why this exception keeps happening. I don't seem to find anything wrong with the 'main' code (see below) and I feel like I've tried everything. Any clue as to what could be causing this?
import java.sql.*;
public class DBTesterApp
{
private static Connection connection = null;
public static void main(String args[])
{
// get the connection and start the Derby engine
connection = MurachDB.getConnection();
if (connection != null)
System.out.println("Derby has been started.\n");
// select data from database
printProducts();
printFirstProduct();
printLastProduct();
printProductByCode("java");
// modify data in the database
Product p = new Product("test", "Test Product", 49.50);
insertProduct(p);
printProducts();
deleteProduct(p);
printProducts();
// disconnect from the database
if (MurachDB.disconnect())
System.out.println("Derby has been shut down.\n");
}
public static void printProducts()
{
try (Statement statement = connection.createStatement();
ResultSet rs = statement.executeQuery("SELECT * FROM Products"))
{
Product p = null;
System.out.println("Product list:");
while(rs.next())
{
String code = rs.getString("ProductCode");
String description = rs.getString("Description");
double price = rs.getDouble("Price");
p = new Product(code, description, price);
printProduct(p);
}
System.out.println();
}
catch(SQLException e)
{
e.printStackTrace(); // for debugging
}
}
public static void printFirstProduct()
{
Product p = null;
// add code that prints the record for the first product in the Products table
System.out.println("First product:");
printProduct(p);
System.out.println();
}
public static void printLastProduct()
{
Product p = null;
// add code that prints the record for the last product in the Products table
System.out.println("Last product:");
printProduct(p);
System.out.println();
}
public static void printProductByCode(String productCode)
{
Product p = null;
// add code that prints the product with the specified code
System.out.println("Product by code: " + productCode);
printProduct(p);
System.out.println();
}
public static void insertProduct(Product p)
{
System.out.println("Insert test: ");
// add code that inserts the specified product into the database
// if a product with the specifed code already exists, display an error message
printProduct(p);
System.out.println();
}
private static void deleteProduct(Product p)
{
System.out.println("Delete test: ");
// add code that deletes the specified product from the database
// if a product with the specified code doesn't exist, display an error message
printProduct(p);
System.out.println();
}
// use this method to print a Product object on a single line
private static void printProduct(Product p)
{
String productString =
StringUtils.padWithSpaces(p.getCode(), 8) +
StringUtils.padWithSpaces(p.getDescription(), 44) +
p.getFormattedPrice();
System.out.println(productString);
}
}
This sequence of code will produce an NPE
as Product
p
has not been instantiated:
Product p = null;
System.out.println("First product:");
printProduct(p);