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

  1. #1
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    Default 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
    Attached Images Attached Images


  2. #2
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    Default Re: Help...so lost where and what did i do wrong?

    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.

  3. #3
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    Default Re: Help...so lost where and what did i do wrong?

    Solved...Thank You

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