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Mike B
Guest
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 Posted: Sat Nov 27, 2004 10:22 pm Post subject: nullpointerexception |
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I'm getting a nullpointerexception in this code. I can't figure out why? Any
ideas how I can investigate?
The exception is when I try to sort an array that I "think" is populated.
=> Arrays.sort(categorySalesArray);
and then I get:
PaneApplication says hello world
Exception in thread "main" java.lang.NullPointerException
at java.util.Arrays.mergeSort(Arrays.java:1156)
at java.util.Arrays.sort(Arrays.java:1080)
at Prob7Application.PaneApplication(Test7Driver.java:42)
at Test7Driver.main(Test7Driver.java:10)
Press any key to continue . . .
import java.text.*;
import java.util.Arrays;
import java.util.Vector;
public class Test7Driver
{
public static void main (String[] args)
{
Prob7Application appSession = new Prob7Application();
appSession.PaneApplication();
System.exit(0);
}
}
class Prob7Application
{
CategorySales[] categorySalesArray = new CategorySales[4];
// constructor
public void Prob7Application()
{
System.out.println("Prob7Application says hello world");
categorySalesArray[0].setCategoryName("XCondiments");
categorySalesArray[0].setCategoryNumber(1);
categorySalesArray[1].setCategoryName("AConfections");
categorySalesArray[1].setCategoryNumber(2);
categorySalesArray[2].setCategoryName("VGrains/Cereal");
categorySalesArray[2].setCategoryNumber(3);
categorySalesArray[3].setCategoryName("Produce");
categorySalesArray[3].setCategoryNumber(4);
System.out.println("Prob7Application says goodbye world");
}
//method header
public void PaneApplication ()
{
System.out.println("PaneApplication says hello world");
Arrays.sort(categorySalesArray);
for (int i=0; i < 4; i++)
{
System.out.println("CatName:" +
categorySalesArray[i].getCategoryName() +
" catNumber:>" +
categorySalesArray[i].getCategoryNumber() +
" CatCount:" +
categorySalesArray[1].getCategoryCount());
}
} //end main
} //end class Prob7PaneApp
class CategorySales implements Comparable
{
// Declare instance variables
private String strCategoryName;
private int intCategoryCount= 0;
private int intCategoryNumber;
public CategorySales()
{
} // end constructor
/** set Category name
*/
public void setCategoryName(String name)
{ strCategoryName = name;
}
/** get Category Name
*/
public String getCategoryName()
{ return strCategoryName;
}
/** set Category number
*/
public void setCategoryNumber(int number)
{ intCategoryNumber = number;
}
/** get Category number
*/
public int getCategoryNumber()
{ return intCategoryNumber;
}
/** add a number to the count of objects sold in this category
*/
public void addCategoryCount(int number)
{ intCategoryCount += number;
}
// Returns category sold counter
public int getCategoryCount()
{ return intCategoryCount;
}
// Implements Comparable Interface
public int compareTo(Object o)
{ CategorySales category2 = (CategorySales) o;
return (this.getCategoryName().compareTo(category2.getCategoryName()));
} //end method compareTo
} // end class CategorySales
</sscce>
Thanks
--
Mike B
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Matt Humphrey
Guest
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| Posted: Sat Nov 27, 2004 10:37 pm Post subject: Re: nullpointerexception |
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"Mike B" <mrcics2000-news-nomail (AT) nomail (DOT) yahoo.com> wrote
| Quote: | I'm getting a nullpointerexception in this code. I can't figure out why?
Any
ideas how I can investigate?
The exception is when I try to sort an array that I "think" is populated.
=> Arrays.sort(categorySalesArray);
and then I get:
PaneApplication says hello world
Exception in thread "main" java.lang.NullPointerException
at java.util.Arrays.mergeSort(Arrays.java:1156)
at java.util.Arrays.sort(Arrays.java:1080)
at Prob7Application.PaneApplication(Test7Driver.java:42)
at Test7Driver.main(Test7Driver.java:10)
Press any key to continue . . .
|
The problem isn't in the sorting... see below.
| Quote: |
sscce
import java.text.*;
import java.util.Arrays;
import java.util.Vector;
public class Test7Driver
{
public static void main (String[] args)
{
Prob7Application appSession = new Prob7Application();
appSession.PaneApplication();
System.exit(0);
}
}
class Prob7Application
{
CategorySales[] categorySalesArray = new CategorySales[4];
|
This allocates an array with 4 slots and the value of each slot is null.
You must explicitly create the CategorySales objects for each entry.
| Quote: |
// constructor
public void Prob7Application()
{
System.out.println("Prob7Application says hello world");
|
This is not a constructor because it has the "void" type even though the
name matches the class name. It is a method that is never called. Drop the
"void."
Here is where you would create the CategorySales items, as:
for (int i = 0; i < categorySalesArray.length; ++i) {
categorySalesArray [i] = new CategorySales ();
}
| Quote: | categorySalesArray[0].setCategoryName("XCondiments");
categorySalesArray[0].setCategoryNumber(1);
categorySalesArray[1].setCategoryName("AConfections");
categorySalesArray[1].setCategoryNumber(2);
categorySalesArray[2].setCategoryName("VGrains/Cereal");
categorySalesArray[2].setCategoryNumber(3);
categorySalesArray[3].setCategoryName("Produce");
categorySalesArray[3].setCategoryNumber(4);
System.out.println("Prob7Application says goodbye world");
}
//method header
public void PaneApplication ()
{
System.out.println("PaneApplication says hello world");
Arrays.sort(categorySalesArray);
for (int i=0; i < 4; i++)
|
Technique note: Don't use a literal--use the actual size of the array.
| Quote: | {
System.out.println("CatName:" +
categorySalesArray[i].getCategoryName() +
" catNumber:>" +
categorySalesArray[i].getCategoryNumber() +
" CatCount:" +
categorySalesArray[1].getCategoryCount());
}
} //end main
} //end class Prob7PaneApp
class CategorySales implements Comparable
{
// Declare instance variables
private String strCategoryName;
private int intCategoryCount= 0;
private int intCategoryNumber;
public CategorySales()
{
} // end constructor
/** set Category name
*/
public void setCategoryName(String name)
{ strCategoryName = name;
}
/** get Category Name
*/
public String getCategoryName()
{ return strCategoryName;
}
/** set Category number
*/
public void setCategoryNumber(int number)
{ intCategoryNumber = number;
}
/** get Category number
*/
public int getCategoryNumber()
{ return intCategoryNumber;
}
/** add a number to the count of objects sold in this category
*/
public void addCategoryCount(int number)
{ intCategoryCount += number;
}
// Returns category sold counter
public int getCategoryCount()
{ return intCategoryCount;
}
// Implements Comparable Interface
public int compareTo(Object o)
{ CategorySales category2 = (CategorySales) o;
return (this.getCategoryName().compareTo(category2.getCategoryName()));
} //end method compareTo
} // end class CategorySales
/sscce
|
I have not checked any deeper for correctness. Let us know what you find
out.
Cheers,
Matt Humphrey [email]matth (AT) ivizNOSPAM (DOT) com[/email] http://www.iviz.com/
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Mike B
Guest
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| Posted: Sat Nov 27, 2004 10:45 pm Post subject: Re: nullpointerexception |
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Matt Humphrey <matth (AT) ivizNOSPAM (DOT) com> wrote:
| Quote: |
I have not checked any deeper for correctness. Let us know what you
find out.
|
D'oh.. how many errors can I make in a small piece of code? Thanks Matt!
--
Mike B
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Mike B
Guest
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| Posted: Sat Nov 27, 2004 10:49 pm Post subject: Re: nullpointerexception - PS |
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Meant to tell you. It worked like a charm after I fixed my mistakes you
pointed out. Thanks again.
--
Mike B
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Skip
Guest
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| Posted: Sun Nov 28, 2004 4:02 pm Post subject: Re: nullpointerexception - PS |
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| Quote: | Meant to tell you. It worked like a charm after I fixed my mistakes you
pointed out. Thanks again.
|
System.out.println("CatName:" +
categorySalesArray[i].getCategoryName() +
" catNumber:>" +
categorySalesArray[i].getCategoryNumber() +
" CatCount:" +
categorySalesArray[1].getCategoryCount());
shouldn't that last 1 be i ?
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Mike B
Guest
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| Posted: Sun Nov 28, 2004 5:26 pm Post subject: Re: nullpointerexception - PS |
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Skip <a@b.invalid> wrote:
| Quote: | Meant to tell you. It worked like a charm after I fixed my mistakes
you pointed out. Thanks again.
System.out.println("CatName:" +
categorySalesArray[i].getCategoryName() +
" catNumber:>" +
categorySalesArray[i].getCategoryNumber() +
" CatCount:" +
categorySalesArray[1].getCategoryCount());
shouldn't that last 1 be i ?
|
LOL, yes, when I tested the real code I spotted that typo. Thanks for
pointing it out though!
--
Mike B
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