Thread: Help...so lost where and what did i do wrong?

Ive attached a screen shot and am hoping someone can point me in the right direction. Here is the code. Thank you in advance

import java.awt.*;
import java.awt.event.*;
import java.awt.datatransfer.*;
import java.text.DecimalFormat;
import javax.swing.JOptionPane;
 
public class Calculator extends Frame implements ActionListener
{
	private Button keys[];
	private Panel keypad;
	private TextField lcd;
	private double op1;
	private boolean foundKey;
	private boolean first;
	private boolean clearText;
	private int lastOp;
	private DecimalFormat calcPattern;
 
public Calculator()
{
	//create an instance of the menu
	MenuBar mnuBar = new MenuBar();
	setMenuBar(mnuBar);
 
	//construct and populate the File menu
	Menu mnuFile = new Menu("File", true);
	mnuBar.add(mnuFile);
		MenuItem mnuFileExit = new MenuItem("Exit");
		mnuFile.add(mnuFileExit);
 
	//construct and populate the edit menu
	Menu mnuEdit = new Menu("Edit", true);
	mnuBar.add(mnuEdit);
		MenuItem mnuEditClear = new MenuItem("Clear");
		mnuEdit.add(mnuEditClear);
		mnuEdit.insertSeparator(1);
		MenuItem mnuEditCopy = new MenuItem("Copy");
		mnuEdit.add(mnuEditCopy);
		MenuItem mnuEditPaste = new MenuItem("Paste");
		mnuEdit.add(mnuEditPaste);
 
	//construct and populate the About menu
	Menu mnuAbout = new Menu("About", true);
		mnuBar.add(mnuAbout);
		MenuItem mnuAboutCalculator = new MenuItem("About Calculator");
		mnuAbout.add(mnuAboutCalculator);
 
		//add the ActionListener to each menu item
		mnuFileExit.addActionListener(this);
		mnuEditClear.addActionListener(this);
		mnuEditCopy.addActionListener(this);
		mnuEditPaste.addActionListener(this);
		mnuAboutCalculator.addActionListener(this);
 
		//assign an ActionCommand to each menu item
		mnuFileExit.setActionCommand("Exit");
		mnuEditClear.setActionCommand("Clear");
		mnuEditCopy.setActionCommand("Copy");
		mnuEditPaste.setActionCommand("Paste");
		mnuAboutCalculator.setActionCommand("About");
 
		//construct components and initialize beginning values
		lcd = new TextField(20);
			lcd.setEditable(false);
		keypad = new Panel();
		keys = new Button[20];
		first = true;
		op1 = 0.0;
		clearText = true;
		lastOp = 0;
		calcPattern = new DecimalFormat("########.########");
 
		//construct and assign captions to the Buttons
		for (int i=0; i<=9; i++)
			keys[i] = new Button(String.valueOf(i));
 
		keys[10] = new Button("/");
		keys[11] = new Button("*");
		keys[12] = new Button("-");
		keys[13] = new Button("+");
		keys[14] = new Button("=");
		keys[15] = new Button(".");
 
		//set Frame and keypad layout to grid layout
		setLayout (new BorderLayout());
		keypad.setLayout(new GridLayout(4,4,10,10));
 
		for (int i=7; i<=10; i++) //7, 8, 9, divide
			keypad.add(keys[i]);
 
		for (int i=4; i<=6; i++) //4, 5, 6
			keypad.add(keys[i]);
 
			keypad.add(keys[11]); //multiply
 
			for (int i=1; i<=3; i++) // 1, 2, 3
				keypad.add(keys[i]);
 
			keypad.add(keys[12]);//subtract
 
			keypad.add(keys[0]); //0 key
 
			for (int i=15; i>=13; i--)
				keypad.add(keys[i]); //decimal point, =, add (+) keys
 
			for (int i=0; i<keys.length; i++)
				keys[i].addActionListener(this);
 
			add(lcd, BorderLayout.NORTH);
			add(keypad, BorderLayout.CENTER);
 
		addWindowListener(
			new WindowAdapter()
				{
				public void windowClosing(WindowEvent e)
					{
						System.exit(0);
				}
			}
	);
 
}// end of constructor method
 
public void actionPerformed(ActionEvent e)
{
	//test for menu item clicks
	String arg = e.getActionCommand();
	if (arg == "Exit")
		System.exit(0);
 
	if (arg == "Clear")
	{
		clearText = true;
		first = true;
		op1 = 0.0;
		lcd.setText("");
		lcd.requestFocus();
	}
 
	if(arg == "Copy")
	{
		Clipboard cb = Toolkit.getDefaultToolkit().getSystemClipboard();
		StringSelection contents = new StringSelection(lcd.getText());
		cb.setContents(contents, null);
	}
 
	if (arg == "Paste")
	{
		Clipboard cb = Toolkit.getDefaultToolkit().getSystemClipboard();
		Transferable content = cb.getContents(this);
		try
		{
			String s = (String)content.getTransferData(DataFlavor.stringFlavor);
			lcd.setText(calcPattern.format(Double.parseDouble(s)));
		}
		catch (Throwable exc)
		{
			lcd.setText("");
		}
	}
 
	if (arg == "About")
	{
		String message ="Calculator ver. 1.0\nOpenExhibit Software\\nCopyright 2007\nAll rights reserved";
		JOptionPane.showMessageDialog(null,message,"About Calculator", JOptionPane.INFORMATION_MESSAGE);
	}
 
	//test for button clicks
	foundKey = false;
 
	//search for the clicked key
	for (int i=0; i<keys.length && !foundKey; i++)
	{
		if(e.getSource() == keys[i])
		{
			foundKey = true;
			switch(i)
			{
				// number and decimal point buttons
				case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7: case 8: case 9: case 15:
					if(clearText)
					{
						lcd.setText("");
						clearText = false;
					}
					lcd.setText(lcd.getText()+ keys[i].getLabel());
					break;
 
					//operator buttons
					case 10: case 11: case 12: case 13: case 14:
						clearText = true;
 
						if(first) // first operand
						{
							if(lcd.getText().length()==0) op1 = 0.0;
							else op1 = Double.parseDouble(lcd.getText());
 
							first = false;
							clearText = true;
							lastOp = i; //save last operator
						}
						else  // second operand
						{
							switch(lastOp)
							{
								case 10: // divide button
									op1 /= Double.parseDouble(lcd.getText());
									break;
								case 11: // multiply button
									op1 *= Double.parseDouble(lcd.getText());
									break;
								case 12: //minus button
									op1 -= Double.parseDouble(lcd.getText());
									break;
								case 13: // plus button
									op1 += Double.parseDouble(lcd.getText());
									break;
							} //end of switch(lastOp)
							lcd.setText(calcPattern.format(op1));
							clearText = true;
 
							if(i==14) first = true; // equal button
							else lastOp = i; // save last operator
						} //end else
						break;
					} // end of switch (i)
				} //end of if
			} // end of for
		} // end of actionPerformed
 
		public static void main(String args[])
		{
			//set frame properties
			Calculator f = new Calculator();
			f.setTitle("Calculator Application");
			f.setBounds(200,200,300,300);
			f.setVisible(true);
 
			//set image properties and add to frame
			Image icon = Toolkit.getDefaultToolkit().getImage("calcImage.gif");
			f.setIconImage(icon);
 
	}//end of main
}//end of class

The error message tells you that you tried to do something with an object that was null (uninitialized) on line 115 of the source file (inside the Calculator constructor). Check that line for a variable that hasn't been given a value.

Solved...Thank You