Null Pointer Exception

[mike hew]

This is what I'm getting and don't understand why.

Can anyone explain why I would? Thank you in advance.

Exception in thread "main" java.lang.NullPointerException
at ShapeTest.loadShapesArray(ShapeTest.java:115)
at ShapeTest.main(ShapeTest.java:20)

line 20 and 115 are in the bold

 public class ShapeTest
{
private static Shape shapes[];
 
public static void main(String args[])
{

int recordNumber = 0;
 
[B]loadShapesArray();[/B]System.out.printf("Record  Shape\n");
System.out.printf("Number  Name\t Dimensions  Coordinates  Radius  Side\t   Area\t   Volume\n");
 
for(Shape currentShape : shapes)
{
String thisShapeDimensions = (" ");
String thisRadius = String.format("%6s", "   -- ");
String thisSide = (" -- ");
String thisArea = (" -- ");
String thisVolume = ("    --  ");
String thisCoordinates = (" ");
 
if(currentShape instanceof TwoDimensionalShape)
{
thisShapeDimensions = String.format("  %-6s", "Two");
TwoDimensionalShape thisTwoDimensionalShape = (TwoDimensionalShape) currentShape;
thisArea = String.format("%,9.2f", ((Square) thisTwoDimensionalShape).getArea());
thisCoordinates = String.format("  (%2d,%2d) ", thisTwoDimensionalShape.getXCoordinate(), 
thisTwoDimensionalShape.getYCoordinate());
}
if(currentShape instanceof Square)
{
Square thisSquare = (Square) currentShape;
thisSide = String.format("%4d", thisSquare.getSide());
} // end if
else if(currentShape instanceof ThreeDimensionalShape)
{
thisShapeDimensions = String.format("  %-6s", "Three");
ThreeDimensionalShape thisThreeDimensionalShape = (ThreeDimensionalShape) currentShape;
thisArea = String.format("%,9.2f", ((Cube) thisThreeDimensionalShape).getArea());
thisVolume = String.format("%,9.2f", ((Cube) thisThreeDimensionalShape).getVolume());
thisCoordinates = String.format("  (%2d,%2d) ", thisThreeDimensionalShape.getXCoordinate(), 
thisThreeDimensionalShape.getYCoordinate());
if(currentShape instanceof Cube)
{
Cube thisCube = (Cube) currentShape;
thisSide = String.format("%4d", thisCube.getSide());
} // end if
} // end if

if(currentShape instanceof Circle)
{
Circle thisShape = (Circle) currentShape;
thisRadius = String.format("%6d", thisShape.getRadius());
} // end if
if(currentShape instanceof Sphere)
{
Sphere thisShape = (Sphere) currentShape;
thisRadius = String.format("%6d", thisShape.getRadius());
} // end if
 
recordNumber++;
 
if(currentShape instanceof Shape){
 
System.out.printf("\n%6s  %-6s    %-10s  %-11s  %6s  %-4s  %-9s  %-9s\n", String.format("  %d  ", recordNumber),
((Square) currentShape).getName(), thisShapeDimensions, thisCoordinates, thisRadius, thisSide, thisArea, thisVolume);

} // end if

} // end for

System.out.println("\nEnd of program");
 
} // end main method
 
//This private static method has no return value, and has no parameters.
private static void loadShapesArray()
{

 
    //INSTANTIATE a local variable named myFile of class MyCsvFile
MyCsvFile myFile = new MyCsvFile("shape_v01.txt");
 
//define local variables
int index = 0;
String [] myFields;
Shape[] shape = shapes;
final int c_shapeNameField = 0;
final int c_xCoordinateField = 1;
final int c_yCoordinateField = 2;
final int c_radiusField = 3;
final int c_sideField = 3;
 
//Get 1st record from CSV file
myFile.readARecord();
 
while (myFile.getEofFound() == false)
{
  myFields = myFile.getCsvRecordFieldArray();
  
if  (myFields[c_shapeNameField].equals(ShapeName.circle)){
[B]shape[index] = (Shape) new Circle(Integer.parseInt(myFields[c_xCoordinateField]),[/B]Integer.parseInt(myFields[c_yCoordinateField]), Integer.parseInt(myFields[c_radiusField]));
}
   else if  (myFields[c_shapeNameField].equals(ShapeName.cube)){
shape[index] = (Shape) new Cube(Integer.parseInt(myFields[c_xCoordinateField]),
Integer.parseInt(myFields[c_yCoordinateField]), Integer.parseInt(myFields[c_sideField]));
   }
   else if  (myFields[c_shapeNameField].equals(ShapeName.sphere)){
shape[index] = (Shape) new Sphere(Integer.parseInt(myFields[c_xCoordinateField]),
Integer.parseInt(myFields[c_yCoordinateField]), Integer.parseInt(myFields[c_radiusField]));
   }
   else if (myFields[c_shapeNameField].equals(ShapeName.square)){
                   shape[index] = (Shape) new Square(Integer.parseInt(myFields[c_xCoordinateField]),
   Integer.parseInt(myFields[c_yCoordinateField]), Integer.parseInt(myFields[c_sideField]),
   Integer.parseInt(myFields[c_sideField]));
      }
   else
  {
//DISPLAY an error message which shows the value of the unknown shape name and its record number. 
System.out.printf("Found unexpected record type of ","Unknown Shape"," at record 5");

}//end if
 
//INCREMENT index
index++;
 
//Get next record, if any
myFile.readARecord();
 
}//end while
 
}//end loadShapesArray
 
} // end class ShapeTest 

[Ernest Friedman-Hill]

The array variables "shape" (and "shapes") are both null; I don't see any attempt to create a Shape[] object for them to refer to. When you try to access shape[index], you'll get a NullPointerException.

[mike hew]

so, probally this is the cause then?

//CREATE the instance variable shapes, an array of Shape objects,
//with myFile.getCountOfRecords() elements

Shape[] shape = shapes;

[Jesper de Jong]

You have a private static variable named 'shapes' at the top of your class that you don't set to a specific value - so it's initialized to null.

In your method loadShapesArray() you do this:

Shape[] shape = shapes;

But since 'shapes' is null, you are just making 'shape' null also. Therefore this line:

shape[index] = (Shape) new Circle(Integer.parseInt(myFields[c_xCoordinateField])

produces a NullPointerException. You have to initialize the array itself somewhere, by doing something like this:

Shape[] shape = new Shape[10];

That makes an array that can hold 10 Shape objects. For more information on how arrays work, see The Java Tutorial: Arrays.