Thread: NullPointerException error

I am fairly new to java I have been working like mad at revamping this code and I feel like I am finally close to a good set up but I am getting this NullPointerException when I try to compile and execute. Any help would really be appreciated as I am stumped maybe my brain is just fried out on this at the moment I dont know.

I hope I posted this all right. The compiler is throwing back there error and it looks like this..........

Exception in thread "main" java.lang.NullPointerException
at Inventory.sortItems(Inventory6.java: 187)
at Inventory6.main(Inventory6.java:21)

 
public class Inventory6 {
 
 
	public static void main(String[] args) {
 
 
        DigitalFeature p1 = new DigitalFeature(1, "Nikon", 24, 65.99,
                          0.0);
        DigitalFeature p2 = new DigitalFeature(2, "Panasonic", 16, 54.00,
                          0.0);
        DigitalFeature p3 = new DigitalFeature(3, "Sony", 20, 75.00,
                          0.0);
 
 
        Inventory inv = new Inventory();
        inv.addItem(p1);
        inv.addItem(p2);
        inv.addItem(p3);
 
        inv.sortItems();
 
        new InventoryGUI(inv).setVisible(true);
 
 
	}
 
}
 
class Camera {
    protected int itemNumber;
    protected static String name;
    protected int unitsInStock;
    protected double unitPrice;
 
    public Camera(int item, String name, int units, double price) {
                this.itemNumber = item;
                this.name = name;
                this.unitsInStock = units;
                this.unitPrice = price;
    }
 
    public int getItemNumber() {
            return itemNumber;
    }
 
    public String getName() {
            return name;
    }
 
    public double getUnitPrice() {
            return unitPrice;
    }
 
    public int getUnitsInStock() {
            return unitsInStock;
    }
 
    public double getValueOfInventory() {
            return unitsInStock * unitPrice;
    }
 
    public void setItemNumber(int itemNumber) {
            this.itemNumber = itemNumber;
    }
 
    public void setName(String name) {
            this.name = name;
    }
 
    public void setUnitPrice(double unitPrice) {
            this.unitPrice = unitPrice;
    }
 
    public void setUnitsInStock(int unitsInStock) {
            this.unitsInStock = unitsInStock;
    }
 
    public String serialize() {
            return String.format("%d|%s|%d|%.2f", itemNumber, name, unitsInStock,
                            unitPrice);
    }
 
}
 
 
class DigitalFeature extends Camera {
    private double imageRes = 0.00;
 
    public DigitalFeature(int item, String newName, int units, double price,
                     double string) {
            super(item, name, units, price);
            this.imageRes = string;
    }
 
    public double getimageRes() {
            return imageRes;
    }
 
    public double getRestockingFee() {
            return 0.05 * getUnitsInStock() * getUnitPrice();
    }
 
    public double getValueOfInventory() {
            return 1.05 * getUnitsInStock() * getUnitPrice();
    }
 
    public void setImageRes(double imageRes) {
            this.imageRes = imageRes;
    }
 
    @Override
    public String serialize() {
            return super.serialize() + String.format("|%s", imageRes);
    }
 
}
 
class Inventory {
    private DigitalFeature[] cameraList;
    private int itemCount = 0;
 
    public Inventory() {
            cameraList = new DigitalFeature[3];
    }
 
    public void addItem(DigitalFeature p) {
            cameraList[itemCount++] = p;
    }
 
    public void deleteItem(int currentIndex) {
            for (int i = currentIndex; i < (getItemCount() - 1); i++) {
                     cameraList[i] = cameraList[i + 1];
            }
            cameraList[getItemCount() - 1] = null;
            itemCount--;
    }
 
    public DigitalFeature getItem(int i) {
            return cameraList[i];
    }
 
    public int getItemByName(String itemName) {
            int item = -1;
            if (itemCount > 0) {
                 for (int i = 0; i < itemCount; i++) {
                      DigitalFeature df = cameraList[i];
                      if (itemName.equalsIgnoreCase(df.getName())) {
                              item = i;
                              break;
                      }
                 }
            }
            return item;
   }
 
   public int getItemCount() {
            return itemCount;
   }
 
   public int getMaxItemNumber() {
            int max = 0;
            if (itemCount > 0) {
                  for (int i = 0; i < itemCount; i++) {
                          DigitalFeature df = cameraList[i];
                          if (df.getItemNumber() > max) {
                                 max = df.getItemNumber();
                          }
                  }
            }
            return max;
   }  
 
   public double getValue() {
             double total = 0.0;
             for (int i = 0; i < getItemCount(); i++) {
                  total += getItem(i).getValueOfInventory();
             }
             return total;
   }
 
   public void sortItems() {
 
            int n = getItemCount();
            for (int search = 1; search < n; search++) {
                   for (int i = 0; i < n - search; i++) {
                          if (cameraList[i].getName().compareToIgnoreCase(
                                              cameraList[i + 1].getName()) > 0) {
 
                                    DigitalFeature temp = cameraList[i];
                                    cameraList[i] = cameraList[i + 1];
                                    cameraList[i + 1] = temp;
                          }
                   }
            }
   } 
 
   public String[] serialize() {
            String[] items = new String[getItemCount()];
            for (int i = 0; i < itemCount; i++) {
                     items[i] = getItem(i).serialize();
            }
            return items;
   }
 
 
 
	}

above is my main section of code
__________________________________________________ ____________________
below is for my GUI

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
 
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
 
 
 
public class InventoryGUI extends JFrame {
 
	private static final long serialVersionUID = 1L;
 
    private static final int NAVIGATION_MODE = 0;
 
    private static final int ADDITION_MODE = 1;
 
    private static final int MODIFICATION_MODE = 2;
 
 
 
    private int currentMode;
 
 
    JTextField itemNumber = new JTextField();
    JTextField name = new JTextField();
    JTextField unitsInStock = new JTextField();
    JTextField unitPrice = new JTextField();
    JTextField valueOfInventory = new JTextField();
    JTextField restockingFee = new JTextField();
    JTextField imageRes = new JTextField();
 
 
    JButton next = new JButton("Next >");
	JButton prior = new JButton("< Prior");
 
	JButton first = new JButton("<< First");
	JButton last = new JButton("Last >>");
 
	JButton add = new JButton("Add");
	JButton delete = new JButton("Delete");
	JButton modify = new JButton("Modify");
 
     JButton saveOrApply = new JButton("Save");
 
     JButton searchOrCancel = new JButton("Search");
 
	JTextField valueOfEntireInventory = new JTextField();
 
	private Inventory inventory;
 
     private int currentIndex = 0;
 
 
	public InventoryGUI(Inventory inventory) {
		super();
		this.inventory = inventory;
 
             setTitle("Inventory GUI - Part 6");
		setBounds(0, 0, 400, 300);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
		createGUI();
		pack();
 
		setLocationRelativeTo(null); // center window
 
             first.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				showFirst();
			}
		});
 
             prior.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				showPrior();
			}
		});
 
             next.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				showNext();
			}
		});
 
 
		last.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				showLast();
			}
		});
 
             add.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				addItem();
			}
		});
 
             delete.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				deleteItem();
			}
		});
 
 
		modify.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				modifyItem();
			}
		});
 
             saveOrApply.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				if (getCurrentMode() == NAVIGATION_MODE) {
					saveInventory();
				} else {
					apply();
				}
			}
		});
 
             searchOrCancel.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				if (getCurrentMode() == NAVIGATION_MODE) {
					searchInventory();
				} else {
					cancel();
				}
			}
		});
 
		updateGUI();
	}
 
     protected void addItem() {
		clearFields();
 
		Integer newItemNumber = inventory.getMaxItemNumber() + 1;
		itemNumber.setText(newItemNumber.toString());
 
		name.requestFocus();
 
		setCurrentMode(ADDITION_MODE);
	}
 
     protected void apply() {
		int newItem = Integer.valueOf(itemNumber.getText());
 
		String newName;
		if ("".equals(name.getText().trim())) {
			showErrorMessage("Please fill the Item Name.");
			name.requestFocus();
			return;
		} else {
			newName = name.getText();
		}
 
		int newUnits;
		try {
			newUnits = Integer.valueOf(unitsInStock.getText());
		} catch (Exception e) {
			showErrorMessage("Invalid value for the field Units In Stock.");
			unitsInStock.requestFocus();
			return;
		}
 
 
		double newUnitPrice;
		try {
			newUnitPrice = Double.parseDouble(unitPrice.getText());
		} catch (Exception e) {
			showErrorMessage("Invalid value for the field Unit Price.");
			unitPrice.requestFocus();
			return;
		}
 
 
             double newImageRes;
             try {
                    newImageRes = Double.parseDouble(imageRes.getText());
             } catch (Exception e) {
                     showErrorMessage("Invalid value for the field Image Resolution.");
                     imageRes.requestFocus();
                     return;
             }
 
		if (currentMode == ADDITION_MODE) {
 
			DigitalFeature df = new DigitalFeature(newItem, newName, newUnits,
					newUnitPrice, newImageRes);
 
			inventory.addItem(df);
			currentIndex = inventory.getItemCount() - 1;
 
		} else if (currentMode == MODIFICATION_MODE) {
 
			DigitalFeature df = inventory.getItem(currentIndex);
			df.setName(newName);
			df.setUnitPrice(newUnitPrice);
			df.setImageRes(newImageRes);
			df.setUnitsInStock(newUnits);
		}
 
		setCurrentMode(NAVIGATION_MODE);
		updateGUI();
	}
 
     protected void cancel() {
		setCurrentMode(NAVIGATION_MODE);
		updateGUI();
	}
 
     private void clearFields() {
		itemNumber.setText("");
		name.setText("");
		unitsInStock.setText("");
		unitPrice.setText("");
		valueOfInventory.setText("");
		restockingFee.setText("");
		imageRes.setText("");
	}
 
     private void createGUI() {
		JPanel itemPanel = new JPanel(new GridLayout(0, 4, 5, 5));
 
		itemPanel.add(new JLabel("Item Number:"));
		itemPanel.add(itemNumber);
		itemNumber.setEditable(false);
 
		itemPanel.add(new JLabel("Item Name:"));
		itemPanel.add(name);
 
		itemPanel.add(new JLabel("Units In Stock: $"));
		itemPanel.add(unitsInStock);
 
		itemPanel.add(new JLabel("Unit Price: $"));
		itemPanel.add(unitPrice);
 
		itemPanel.add(new JLabel("Value of Inventory: $"));
		itemPanel.add(valueOfInventory);
		valueOfInventory.setEditable(false);
 
		itemPanel.add(new JLabel("Restocking Fee: $"));
		itemPanel.add(restockingFee);
		restockingFee.setEditable(false);
 
             itemPanel.add(new JLabel("Image Resolution:"));
		itemPanel.add(imageRes);
 
             itemPanel.add(new JLabel("Value of Entire Inventory: $"));
		itemPanel.add(valueOfEntireInventory);
		valueOfEntireInventory.setEditable(false);
 
		JPanel inventoryPanel = new JPanel(new BorderLayout(5, 5));
		inventoryPanel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
 
		inventoryPanel.add(new LogoPanel(getWidth(), 80), BorderLayout.NORTH);
 
		inventoryPanel.add(itemPanel, BorderLayout.CENTER);
 
		JPanel bottomPanel = new JPanel(new GridLayout(2, 1, 5, 5));
 
             JPanel navigationPanel = new JPanel(new GridLayout(1, 7, 5, 5));
		navigationPanel.add(first);
		navigationPanel.add(prior);
		navigationPanel.add(add);
		navigationPanel.add(delete);
		navigationPanel.add(modify);
		navigationPanel.add(next);
		navigationPanel.add(last);
		bottomPanel.add(navigationPanel);
 
		JPanel extraPanel = new JPanel(new GridLayout(0, 2, 5, 5));
		extraPanel.add(saveOrApply);
		extraPanel.add(searchOrCancel);
		bottomPanel.add(extraPanel);
 
		inventoryPanel.add(bottomPanel, BorderLayout.SOUTH);
		setContentPane(inventoryPanel);
 
		setCurrentMode(NAVIGATION_MODE);
	}
 
     protected void deleteItem() {
		if (isInventoryEmpty()) {
			return;
		}
		if (JOptionPane.showConfirmDialog(this,
				"Do you really want to delete this item?", "Confirmation",
				JOptionPane.YES_NO_OPTION) == JOptionPane.YES_OPTION) {
			inventory.deleteItem(currentIndex);
			currentIndex = inventory.getItemCount() - 1;
			updateGUI();
		}
	}
 
	public int getCurrentMode() {
		return currentMode;
	}
 
     private boolean isInventoryEmpty() {
		if (inventory.getItemCount() == 0) {
			JOptionPane.showMessageDialog(this, "The Inventory is Empty!");
			return true;
		}
		return false;
	}
 
     protected void modifyItem() {
		if (isInventoryEmpty()) {
			return;
		}
		setCurrentMode(MODIFICATION_MODE);
	}
 
     protected void saveInventory() {
		if (isInventoryEmpty()) {
			return;
		}
		String[] items = inventory.serialize();
 
		File file;
 
		file = new File("c:\\data");
		if (!file.exists()) {
			file.mkdir();
		}
 
		file = new File("c:\\data\\inventory.dat");
		if (file.exists()) {
			file.delete();
		}
 
		try {
			file.createNewFile();
		} catch (IOException e) {
			showErrorMessage("Failed to create the Inventory file.");
			return;
		}
 
		try {
			FileWriter fw = new FileWriter(file);
			for (int i = 0; i < items.length; i++) {
				fw.write(items[i] + "\n");
			}
			fw.close();
 
			JOptionPane.showMessageDialog(this, "File successfully saved!");
		} catch (IOException e) {
			showErrorMessage("Failed to write the Inventory file.");
		}
	}
 
     protected void searchInventory() {
		if (isInventoryEmpty()) {
			return;
		}
		String itemName = JOptionPane.showInputDialog(this,
				"Enter the Item Name", "Search Item",
				JOptionPane.QUESTION_MESSAGE);
 
		if (itemName != null) {
			int item = inventory.getItemByName(itemName);
			if (item != -1) {
				currentIndex = item;
				updateGUI();
			} else {
				showErrorMessage(String.format("Item \"%s\" not found.",
						itemName));
			}
		}
	}
 
     public void setCurrentMode(int currentMode) {
		this.currentMode = currentMode;
 
		switch (currentMode) {
 
		case ADDITION_MODE:
		case MODIFICATION_MODE:
			first.setEnabled(false);
			prior.setEnabled(false);
			add.setEnabled(false);
			modify.setEnabled(false);
			delete.setEnabled(false);
			next.setEnabled(false);
			last.setEnabled(false);
			saveOrApply.setText("Apply");
			searchOrCancel.setText("Cancel");
			setFieldsEditable(true);
			break;
 
             case NAVIGATION_MODE:
			first.setEnabled(true);
			prior.setEnabled(true);
			add.setEnabled(true);
			modify.setEnabled(true);
			delete.setEnabled(true);
			next.setEnabled(true);
			last.setEnabled(true);
			saveOrApply.setText("Save");
			searchOrCancel.setText("Search");
			setFieldsEditable(false);
			break;
		}
	}
 
     protected void setFieldsEditable(boolean editable) {
		name.setEditable(editable);
		unitsInStock.setEditable(editable);
		unitPrice.setEditable(editable);
		imageRes.setEditable(editable);
	}
 
     private void showErrorMessage(String message) {
		JOptionPane.showMessageDialog(this, message, "Error",
				JOptionPane.ERROR_MESSAGE);
	}
 
     protected void showFirst() {
		if (isInventoryEmpty()) {
			return;
		}
		currentIndex = 0;
		updateGUI();
	}
 
     protected void showLast() {
		if (isInventoryEmpty()) {
			return;
		}
		currentIndex = inventory.getItemCount() - 1;
		updateGUI();
	}
 
     private void showNext() {
		if (isInventoryEmpty()) {
			return;
		}
		if (currentIndex < inventory.getItemCount() - 1) {
			currentIndex++;
			updateGUI();
		} else {
			showFirst();
		}
	}
 
     private void showPrior() {
		if (isInventoryEmpty()) {
			return;
		}
		if (currentIndex > 0) {
			currentIndex--;
			updateGUI();
		} else {
			showLast();
		}
	}
 
     public void updateGUI() {
		if (currentIndex != -1) {
			DigitalFeature item = inventory.getItem(currentIndex);
 
			itemNumber.setText(String.valueOf(item.getItemNumber()));
			name.setText(item.getName());
			unitsInStock.setText(String.valueOf(item.getUnitsInStock()));
			unitPrice.setText(String.format("%.2f", item.getUnitPrice()));
			valueOfInventory.setText(String.format("%.2f", item
					.getValueOfInventory()));
			restockingFee.setText(String
					.format("%.2f", item.getRestockingFee()));
 
 
		} else {
			clearFields();
		}
 
		valueOfEntireInventory.setText(String.format("%.2f", inventory
				.getValue()));
	}
}

__________________________________________________ ______________________

last is for my logo

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
 
import javax.swing.JPanel;
 
public class LogoPanel extends JPanel {
 
       private static final long serialVersionUID = 1L;
 
       public LogoPanel(int width, int height) {
		super();
		setPreferredSize(new Dimension(width, height));
	}
 
        @Override
	public void paint(Graphics g) {
		g.setColor(Color.WHITE);
		g.fill3DRect(0, 0, getWidth(), getHeight(), true);
 
		int midX = getWidth() / 2;
		int midY = getHeight() / 2;
 
		g.setColor(Color.LIGHT_GRAY);
		g.fillOval(midX - 100, midY - 25, 50, 50);
 
		g.setColor(Color.BLACK);
		g.setFont(new Font("Verdana", Font.BOLD, 24));
		g.drawString("Camera Hut", midX - 70, midY + 10);
	}
 
}

__________________________________________________ ____________________

That's way too much code to wade through, but the Exception is telling you what's wrong: on line 187, you're dereferencing a null Object. You can't do that. Make sure that all of your variables reference an instance of something before you use them.