This is a college course assignment that creates a ItemRecord class and implements Serializable with getter and setters, then overrides the toString method. Next I created a ItemRecordReport class with a Scanner object mapped to an input file "ItemRecord_text.txt". Created an ObjectOutputStream object mapped to a binary output file "ItemRecord_binary.txt". Created an ObjectInputStream object mapped to the binary file. Everything works. I modified this post by putting in an array in method main and changing the field values with a additional text document. My error is a NullPointerException: This is the stack trace
Item Cost Quantity Description
Number
A100 $ 99.99 10 Canon PowerShot-135
A200 $149.99 50 Panasonic-Lumix T55
A300 $349.99 20 Nikon- D3200 DSRL
A400 $280.99 30 Sony- DSC-W800
A500 $ 97.99 20 Samsung- WB35F
Exception in thread "main" java.lang.NullPointerException
at ItemRecordReport.endRecord(ItemRecordReport.java:165)
at ItemRecordReport.main(ItemRecordReport.java:156)
----jGRASP wedge2: exit code for process is 1.
----jGRASP: operation complete.
//create program so that objects of class can be serialized, implements interface Serialiable //create constructor with 4 parameters with accompanying get and set methods, Override toString method //create text file with 5 records, create Scanner object,ObjectOutputStream, and ObjectInputStream //create new ItemRecord object, change values of all fields in ItemRecord object using object's set methods //modify ItemRecord object using toString method
import java.io.Serializable;
public class ItemRecord implements Serializable
{ //declare 4 fields with private access
private String itemNumber;
private double cost;
private int quantity;
private String description;
//constructor with no arguments call other constructor with default values
public ItemRecord()
{
this("",0.0,0,"");
}//end constructor with no arguments
//constructor with 4 arguments
public ItemRecord(String number, double price, int quant, String desc)
{
setItemNumber(number);
setCost(price);
setQuantity(quant);
setDescription(desc);
}//end constructor
public void setItemNumber(String number)
{
itemNumber = number;
}//end setItemNumber
public String getItemNumber()
{
return itemNumber;
}//end getItemNumber
public void setCost(double price)
{
cost = price;
}//end seCost
public double getCost()
{
return cost;
}//end getCost
public void setQuantity(int quant)
{
quantity = quant;
}//end setQuantity
public int getQuantity()
{
return quantity;
}//end getQuantity
public void setDescription(String desc)
{
description = desc;
}//end setDescription
public String getDescription()
{
return description;
}//end getDescription
public static void printHeading()
{
System.out.println("Item Cost Quantity Description");
System.out.print("Number");
System.out.println();
}
public String toString()
{
return this.getItemNumber()+String.format(" $%6.2f ",+this.getCost())+String.format("%4d ",+this.getQuantity())+this.getDescription();
}
}//end class ItemRecord
Here is the other test class: This class contain the ObjectOutputStream and ObjectInputStream objects. Therefore method main is here as well as the ItemRecordReport object that I use to call the methods in main.
import java.io.*;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.util.Scanner;
public class ItemRecordReport
{ private ObjectOutputStream output;//writes to binary
private ObjectInputStream binInFile;//reads binary
private Scanner input;
public void openInputBinaryFile()
{//create a ObjectInputStream object that will read a binary file
try
{
binInFile = new ObjectInputStream(new FileInputStream("ItemRecord_binary.txt"));
}//end try
catch (IOException ioException)
{
System.out.println("Error opening file.");
}//end catch
}//end openInputBinaryFile
public void openOutputBinaryFile()
{
//creating a binary objectOutputStream text file
try
{
output = new ObjectOutputStream(
new FileOutputStream("ItemRecord_binary.txt"));
}//end try
catch (IOException ioException)
{
System.err.println("Error opening file");
}
}//end openOutputBinaryFile
public void readInputTextRecords()
{
ItemRecord record;
String itemNumber;
double cost;
int quantity;
String description;
try
{
input = new Scanner(new File("ItemRecord_text.txt"));
}
catch (IOException e)
{
System.out.println("Error file not found");
}//end catch
while(input.hasNext())
{
try{
itemNumber = input.next();
cost = input.nextDouble();
quantity = input.nextInt();
description = input.nextLine();
record = new ItemRecord(itemNumber,cost,quantity,description);
//writing into the binary text file
output.writeObject(record);
}
catch (IOException ioException)
{
System.out.println("Error writing to binary file.");
return;
}
}
}//end readInputRecords
public void readInputBinaryRecords()
{
openInputBinaryFile();
ItemRecord otherRecord;
try
{ while (true)
{
otherRecord = (ItemRecord) binInFile.readObject(); //use down cast
System.out.println(otherRecord.toString());
}
}
catch (EOFException e)
{
return;
}//end catch
catch (ClassNotFoundException e)
{
System.err.println("Unable to create object.");
}//end catch
catch (IOException ioException)
{
System.err.println("Error reading from binary file.");
}//end catch
}//readInputBinaryRecords
public void closeBinaryOutputFile()
{
try
{ if (output !=null )
output.close();
}//end try
catch ( IOException ioException)
{
System.out.println( "Error closing file");
System.exit(1);
}//end catch
}//end closeBinaryOutputFile
public void closeBinaryInputFile()
{
try
{ if (binInFile != null )
binInFile.close();
else
System.out.println("No records were written to the binary file!");
}//end try
catch ( IOException ioException)
{
System.out.println( "Error closing file");
System.exit(1);
}//end catch
}//end closeBinaryFile
public static void main(String[] args)
{
ItemRecordReport object = new ItemRecordReport();
ItemRecord.printHeading();//print heading
object.openOutputBinaryFile();//opens the binary file
object.readInputTextRecords();//reads text file and writes to binary file
object.closeBinaryOutputFile();//closes the binaryOutputFile
object.openInputBinaryFile();//opens binary file
object.readInputBinaryRecords();
object.closeBinaryInputFile();
Scanner inFile;
ItemRecord[] itemRecord = new ItemRecord[5];
itemRecord[x] = new ItemRecord();
for (int x = 0; x <= 4; x++){
itemRecord[x].setItemNumber("");
itemRecord[x].setCost(0);
itemRecord[x].setQuantity(0);
itemRecord[x].setDescription("");
}
try
{
inFile = new Scanner(new File("itemRecord.txt"));
while(inFile.hasNext())
{
for(int count =0; count<=4; count++)
{
itemRecord[count].setItemNumber(inFile.next());
itemRecord[count].setCost(inFile.nextDouble());
itemRecord[count].setQuantity(inFile.nextInt());
itemRecord[count].setDescription(inFile.next());
}//end for loop
}//end while
}
catch (IOException e)
{
System.out.println("Error file not found");
}//end catch
try
{
ObjectOutputStream binOutFile = new ObjectOutputStream
(new FileOutputStream("ItemRecord_binary.txt"));
}//end try
catch (IOException e)
{
System.err.println("error opening file");
}
System.out.println(itemRecord.toString());
}//end method main
}//end class ItemRecordReport
And here is the text file:
A100 99.99 10 Canon PowerShot-135
A200 149.99 50 Panasonic-Lumix T55
A300 349.99 20 Nikon- D3200 DSRL
A400 280.99 30 Sony- DSC-W800
A500 97.99 20 Samsung- WB35F
This is the new text file to change the field values:
B100 98.00 10 ABC1010
B200 97.00 15 DEF1020
B300 96.00 10 GHI1030
B400 95.00 05 JKL1040
B500 94.00 01 MNO1050
Error stack trace
Item Cost Quantity Description
Number
A100 $ 99.99 10 Canon PowerShot-135
A200 $149.99 50 Panasonic-Lumix T55
A300 $349.99 20 Nikon- D3200 DSRL
A400 $280.99 30 Sony- DSC-W800
A500 $ 97.99 20 Samsung- WB35F
Exception in thread "main" java.lang.NullPointerException
at ItemRecordReport.endRecord(ItemRecordReport.java:165)
at ItemRecordReport.main(ItemRecordReport.java:156)
----jGRASP wedge2: exit code for process is 1.
----jGRASP: operation complete.
There are numerous problems here. The NullPointerException comes from the fact that you've initialized the ItemRecord[] array but not any of its elements. You need to add
itemRecord[x] = new ItemRecord();
above line 153.
However there are other problems.
You are making up your own error messages instead of printing the much more useful exception messages themselves, or, as you are still debugging, printing the stack trace. For example:
catch (IOException ioException)
{
ioException.printStackTrace();
}
You are catching exceptions and proceeding as though they didn't happen. Code that depends on the success of code in a try block should be inside the same try block. For example:
try
{
input = new Scanner(new File("ItemRecord_text.txt"));
}
catch (IOException e)
{
e.printStackTrace();
}//end catch
while (input.hasNext())
// ...
should be
try
{
input = new Scanner(new File("ItemRecord_text.txt"));
while (input.hasNext())
// ...
}
catch (IOException e)
{
e.printStackTrace();
}//end catch
You aren't scanning the "ItemRecord.txt" file correctly. It has five columns but you're only scanning four of them. Left as an exercise for the reader.
I suggest you get out of the habit of writing
} // end catch
etcetera. Modern IDEs and proper indentation make this completley unnecessary, and it actually gets in the way in practice and they can often end up wrong. You've probably been taught it in school, and you should certainly do whatever you have to do to get the grades you want, but out here people don't do it much. Haven't seen it for decades.