GUI Headache

**Nepomuk** · Sep 25 '07, 08:25 AM

Originally posted by pixiedustjt

Hello,

I'm currently working on the dreaded Inventory Program. I'm on part four and just learning GUIs. I need to modify the Inventory Program to use a GUI. In the GUI, it should display the information in my array one line at a time as well as the value of my entire inventory, additional feature and restocking fee. I was able to create the GUI, but I can't populate it with my array items. Any tips on getting my array information to display on the GUI would be wonderful! I am able to compile the file, but get an empty GUI.

Any assistance is greatly appreciated!!!! !

Here is my array code and the dispaly call to the GUI in my Main class:
...

Hi!
I would add a setItem(...) method to the GUI, which set's the contents of those JLabels. It can get it's information from your Inventory and write it into the Labels with setText("Blabla : " + valueToBeSet).

Otherwise, you'll just have to keep on trying.

Greetings,
Nepomuk

**pixiedustjt** · Sep 25 '07, 12:08 PM

Thank you! I will try that and let you know!

**pixiedustjt** · Sep 25 '07, 04:48 PM

I've been playing around with this for hours and I'm still stuck. Can you post an example of how to add a setItem method to the GUI?

Thanks again!

**r035198x** · Sep 25 '07, 04:54 PM

Originally posted by pixiedustjt

I've been playing around with this for hours and I'm still stuck. Can you post an example of how to add a setItem method to the GUI?

Thanks again!

Well then what code do you have now and where are you stuck with it?

**JosAH** · Sep 25 '07, 05:19 PM

Originally posted by pixiedustjt

I've been playing around with this for hours and I'm still stuck. Can you post an example of how to add a setItem method to the GUI?

Thanks again!

Please don't beg for code; if you read the API documentatio you'd find lots and
lots of code examples and explanations. Try to think in detail about the problem
you're supposed to be working on. It's the only way to slaughter the problem and
master the Java language.

kind regards,

Jos

**pixiedustjt** · Sep 25 '07, 05:53 PM

Here is my current code. I am trying to get my array items to display in the GUI. The file compiles, but I get the following error message when the GUI tries to lauch.

Exception in thread "main" java.lang.NullP ointerException
at Labels.<init>(L abels.java:36)
at Inventory_Progr am4.<init>(Inve ntory_Program4. java:98)
at Inventory_Progr am4.main(Invent ory_Program4.ja va:121)

I know that the following line is giving me the grief (bookTitleLabel .setText("The Book Title is: " + myBook[i].getBookTitle() );). I'm trying to display the array item, but not doing it correctly.

I am so lost on how to incorporate my array information into the GUI. I apologize if I sound like I'm begging for code, that was not my intention. Thanks for all of your help!

The following code is where I created my GUI:

Code:

import java.awt.FlowLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
import javax.swing.Icon;
import javax.swing.ImageIcon;

public class Labels extends JFrame
{
	
private Book2 myBook[];


	private JLabel bookTitleLabel;
	private JLabel itemNumberLabel;
	private JLabel bookUnitsLabel;
	private JLabel bookPriceLabel;
	private JLabel inventoryValueLabel;
	private JLabel bookAuthorLabel;
	private JLabel bookRestockingFeeLabel;
	private JLabel totalInventoryValueLabel;

	//  Labels constructor adds JLabels to JFrame
	public Labels()
	{
	super( "Inventory Program" );
	setLayout( new FlowLayout() ); // set frame layout


	
	for (int i = 0; i<5; i++)
	{
	
	// JLabel constructor
	bookTitleLabel = new JLabel();
	bookTitleLabel.setText("The Book Title is: " + myBook[i].getBookTitle());
	bookTitleLabel.setToolTipText("Book Title Label");
	add( bookTitleLabel ); // add bookTitleLabel to JFrame

	itemNumberLabel = new JLabel("Item Number:");
	itemNumberLabel.setToolTipText("Item Number Label");
	add( itemNumberLabel ); // add itemNumberLabel to JFrame

	bookUnitsLabel = new JLabel("Book Units:");
	bookUnitsLabel.setToolTipText("Book Units Label");
	add( bookUnitsLabel ); // add bookUnitsLabel to JFrame

	bookPriceLabel = new JLabel("Book Price:");
	bookPriceLabel.setToolTipText("Book Price Label");
	add( bookPriceLabel ); // add bookPriceLabel to JFrame
	
	inventoryValueLabel = new JLabel("Book Inventory Value:");
	inventoryValueLabel.setToolTipText("Inventory Value Label");
	add ( inventoryValueLabel ); // add inventoryValueLabel to JFrame

	bookAuthorLabel = new JLabel("Book Author:");
	bookAuthorLabel.setToolTipText("Book Author Label");
	add( bookAuthorLabel ); // add bookAuthorLabel to JFrame
	
	bookRestockingFeeLabel = new JLabel("Restocking Fee:");
	bookRestockingFeeLabel.setToolTipText("Restocking Fee Label");
	add( bookRestockingFeeLabel ); // add bookRestockingFeeLabel to JFrame

	totalInventoryValueLabel = new JLabel("Total Inventory Value:");
	totalInventoryValueLabel.setToolTipText("Total Inventory Label");
	add( totalInventoryValueLabel ); // add totalInventoryValueLabel to JFrame
}
	} // end Label constructor
} // end class Labels

The following code is my array in my Main class:

Code:

// constructor
	public Inventory_Program4()
	{		
		double totalInventoryValue = 0.0;

		// Specify how many items are in the array
		// instantiate Book2 object
		myBook = new Book2[5];
		myBook[0] = new Book2("The Key Triology", 1, 25, 7.99, "Nora Roberts");
		myBook[1] = new Book2("The Shinning", 2, 15, 5.99, "Stephen King");
		myBook[2] = new Book2("Wild Acre", 3, 7, 4.99, "Phillipa Gregory");
		myBook[3] = new Book2("Dark Paradise", 4, 2, 12.99, "Tami Hoag");
		myBook[4] = new Book2("Dollhouse Murders", 5, 18, 2.95, "Betty Ren Wright");
			
		// call method sort book inventory for display
		sortBookInventory();

		for (int i = 0; i<5; i++)
		{

			// display the book title
			System.out.println("The book title is: " + myBook[i].getBookTitle());

			// display the item number
			System.out.println("The item number is: " + myBook[i].getItemNumber());

			// display the number of units in stock
			System.out.println("The number of units in stock is: " + myBook[i].getBookUnits());

			// display the price per book
			System.out.printf("The price of the book is: $%.2f\n", myBook[i].getBookPrice());

			// display the value of the inventory
			System.out.printf("The value of the inventory is: $%.2f\n", myBook[i].inventoryValue());

			// display the book author
			System.out.println("The book author is: " + myBook[i].getBookAuthor());

			// display the restocking fee
			System.out.println("Restock Fee: " + myBook[i].inventoryValue() * 0.05);

			// calculate total inventory value with restocking fee added
			totalInventoryValue += (myBook[i].inventoryValue() * 1.05);

			// insert blank line
			System.out.println();


		} // end for

		// display the total value of the inventory with the restocking fee
		System.out.printf("The total value of the book inventory including the restocking fee is: $%5.2f.\n", totalInventoryValue);

		// display the total value of the inventory excluding the restocking fee
		System.out.println("The total value of the book inventory is: " + totalInventoryValue());

			// calling GUI to display contents
			Labels labels = new Labels(); // create Labels
			labels.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
			labels.setSize(275, 180); // set frame size
			labels.setVisible( true ); // display frame

	} // end constructor

**r035198x** · Sep 25 '07, 06:02 PM

private Book2 myBook[];

Does not create an array at all.
myBook at this point is null. So when the code reaches that point in that Labels constructor and tries to do myBook[i].getWhatever it tells you that you are derefencing a null variable. The exception trace does tell you what is wrong as you can see.

GUI Headache

GUI Headache

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