Any Java programmers? Need help with IOStream.

[sailorman444]

Hi guys,

So I have been using Java for 6 months and I have come across a problem.

I have a program where you populate a hashmap through textboxes and a combobox. I also have an add button which adds the information to the hashmap. When I exit the program through the use of a menubar the hashmap is then written to a .ser file. I also have a form which a textarea to display all the data that has been populated into the hashmap.

When the program is closed the .ser has been written, but when I open the program again it does not populate the hashmap as I can no longer see the populated entries in the textarea, nor does it allow me to add data to the .ser file.

(Terrible explanation, I know)

Hopefully the code below will explain what I can't.

  //Code on my main menu for file creation / reading to the hashmap

		try
		{
			ObjectInputStream ois =  new ObjectInputStream(new FileInputStream("carFile.ser"));
			HashMap<String, Car> cars = (HashMap<String, Car>)ois.readObject();
			ois.close();
		}

		catch(ClassNotFoundException cnfx)
		{
			JOptionPane.showMessageDialog(null, "The data could not be read.");
			cnfx.printStackTrace();
		}
		catch(FileNotFoundException fnfx)
		{
			JOptionPane.showMessageDialog(null, "No file found.");
			fnfx.printStackTrace();
		}
		catch(IOException iox)
		{
			JOptionPane.showMessageDialog(null, "Could not read from file.");
			iox.printStackTrace();
		}

//Code to output data to .ser file, also on main menu

		if ( s.equalsIgnoreCase("Exit"))
		{
			try{
				
				ObjectOutputStream oos =  new ObjectOutputStream(new FileOutputStream("carFile.ser"));
				oos.writeObject(cars);
				oos.close();
			}
			catch(FileNotFoundException fnfx)
			{
				JOptionPane.showMessageDialog(null, "No file found!");
				fnfx.printStackTrace();
			}
			
			catch(IOException iox)
			{
				JOptionPane.showMessageDialog(null, "Could not write file");
				iox.printStackTrace();
			}
			System.exit(0);
		}

//Code on Display page, which stops working after I close the program after the file has been created.

		if ( e.getSource()==btnExit)
		{
			txtArea.setText("");
			this.setVisible(false);
		}
			
		else if ( e.getSource()==btnDisplay)
		{
			txtArea.setText("");
			
			String s;
			s="Reg No.   Make             Model             Description        						Colour		Category		Mileage		Year	Cost(£)		Selling Price(£)\n";
			txtArea.append(s);									
			s="------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\n";
			txtArea.append(s);
			
			Set set = cars.entrySet();
			Iterator i = set.iterator();
			
			while (i.hasNext())
			{
				Map.Entry me = (Map.Entry)i.next();
				s = me.getValue() + "\n";
				txtArea.append(s);
			}

I have searched the intenet for hours and have not found a similar problem.

Thank you
-Sailorman444

[mutexe]

So I have been using Java for 6 months and I have come across a problem.

Your first problem is creating a thread in the wrong forum.

[sailorman444]

I come to this forum because I have had a lot of help on C++ and remember seeing people posting questions about Java.

[coder777]

Line 6: the new local variable cars shadows the member cars which is not modified

ie:

		try
		{
			ObjectInputStream ois =  new ObjectInputStream(new FileInputStream("carFile.ser"));
			HashMap<String, Car> cars = (HashMap<String, Car>)ois.readObject();
			ois.close();
		}

[sailorman444]

Tried the above method. I don't think the file is reading in as it is not populating the hashmap even after creating and writing to the file, once I close the program nothing displays, and it does not allow to add to the file. Tested this by using my textarea which displays all the data using an iterator