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Thread: Problem understanding Java code modification

  1. #1
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    Default Problem understanding Java code modification

    The following is a problem that just does addition. I need to modify it to include buttons and calculation for multiplication,division and subtraction. Regarding the section that shows the addition portion of program, do i just take those same lines and,inserting the different operations, add those lines to the code after the addition or am i way off? just want to know in order to modify program to include all operations if i just simply need to add other operations after the addition or is there something i am not seeing. Thank you



    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
     
    import javax.swing.JButton;
    import javax.swing.JFrame;
    import javax.swing.JPanel;
    import javax.swing.JTextField;
     
    public class BasicCalculator {
    	private static final int FRAME_WIDTH = 150;
    	private static final int FRAME_HEIGHT = 120;
     
    	// Keeps track of the current operation (subtract, add, etc)
    	private static final int NO_OPERATION = 0;
    	private static final int ADDITION = 1;
    	public static int operation = NO_OPERATION;
     
    	public static JTextField textFieldDisplay;
    	public static double Value1 = 0; // holds the value before the operation
     
    	public static void main(String[] args) {
    		// Set up the user interface
    		JFrame frame = new JFrame();
    		JPanel buttonPanel = new JPanel();
    		frame.add(buttonPanel);
     
    		// create two buttons, plus and equal and a text box for answers
    		textFieldDisplay = new JTextField(10);
    		buttonPanel.add(textFieldDisplay);
    		JButton buttonPlus = new JButton(" + ");
    		buttonPanel.add(buttonPlus);
    		JButton buttonEqual = new JButton(" = ");
    		buttonPanel.add(buttonEqual);
     
    		frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
    		frame.setTitle("Basic Calculator");
    		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    		frame.setVisible(true);
     
     
    		// called when the equal sign '=' is pressed
    		class EqualSignListener implements ActionListener {
     
    			public void actionPerformed(ActionEvent event)
    			{
    				double Value2 = Double.parseDouble(textFieldDisplay.getText());
    				if (operation == ADDITION) {
    					// plus sign pressed before the equal sign
    					Value2 += Value1;
    				}
    				// Convert from a answer to a string
    				Double answer = new Double(Value2);
    				textFieldDisplay.setText( answer.toString() );
    				// Reset the operation to show no current operation
    				operation = NO_OPERATION;
    			}
    		}
     
    		// called when a plus sign '+' is pressed
    		class PlusSignListener implements ActionListener {
    			public void actionPerformed(ActionEvent event)
    			{
    				Value1 = Double.parseDouble(textFieldDisplay.getText());
    				operation = ADDITION;
    			}
    		}
     
    		// Add the methods that will be called when these buttons are pressed
    		ActionListener plusSignListener = new PlusSignListener();
    		buttonPlus.addActionListener(plusSignListener);
     
    		ActionListener equalSignListener = new EqualSignListener();
    		buttonEqual.addActionListener(equalSignListener);
     
    	}
    Last edited by helloworld922; June 25th, 2011 at 02:23 PM.


  2. #2
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    Default Re: Problem understanding Java code modification

    Since those operations all take two operands, you should be able to use the logic for the add with the other three operations. That would be the simplest way.
    Another more OOP technique could involve a base class and extended classes for each of the operators.
    An evaluate() method would take two operands, do the operation and return a value.
    The main program would have a HashMap to look up the class object to use with the operator as the key.


    Please enclose your posted code in code tags to preserve formatting. Use the # icon

  3. #3
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    Default Re: Problem understanding Java code modification

    So just take the information within the aditon section of the code and add it after the addition section just chnaging the adition portions to the appropriate operations?

  4. #4
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    Default Re: Problem understanding Java code modification

    Yes that should work. The code for the four operations should be almost the same except for the operation itself.

  5. #5
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    Default Re: Problem understanding Java code modification

    How would you add next section to ensure it is in proper place? after what line?

  6. #6
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    Default Re: Problem understanding Java code modification

    Here is what i did..is this correct for my problem where I need to modify it to include buttons and calculation for multiplication,division and subtraction.?

    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
     
    import javax.swing.JButton;
    import javax.swing.JFrame;
    import javax.swing.JPanel;
    import javax.swing.JTextField;
     
    public class BasicCalculator {
    	private static final int FRAME_WIDTH = 150;
    	private static final int FRAME_HEIGHT = 120;
     
    	// Keeps track of the current operation (subtract, add, etc)
    	private static final int NO_OPERATION = 0;
    	private static final int ADDITION = 1;
    	public static int operation = NO_OPERATION;
     
    	public static JTextField textFieldDisplay;
    	public static double Value1 = 0; // holds the value before the operation
     
    	public static void main(String[] args) {
    		// Set up the user interface
    		JFrame frame = new JFrame();
    		JPanel buttonPanel = new JPanel();
    		frame.add(buttonPanel);
     
    		// create two buttons, plus and equal and a text box for answers
    		textFieldDisplay = new JTextField(10);
    		buttonPanel.add(textFieldDisplay);
    		JButton buttonPlus = new JButton(" + ");
    		buttonPanel.add(buttonPlus);
    		JButton buttonEqual = new JButton(" = ");
    		buttonPanel.add(buttonEqual);
     
    		frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
    		frame.setTitle("Basic Calculator");
    		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    		frame.setVisible(true);
     
     
    		// called when the equal sign '=' is pressed
    		class EqualSignListener implements ActionListener {
     
    			public void actionPerformed(ActionEvent event)
    			{
    				double Value2 = Double.parseDouble(textFieldDisplay.getText());
    				if (operation == ADDITION) {
    					// plus sign pressed before the equal sign
    					Value2 += Value1;
    				}
    				// Convert from a answer to a string
    				Double answer = new Double(Value2);
    				textFieldDisplay.setText( answer.toString() );
    				// Reset the operation to show no current operation
    				operation = NO_OPERATION;
    			}
    		}
     
    		// called when a plus sign '+' is pressed
    		class PlusSignListener implements ActionListener {
    			public void actionPerformed(ActionEvent event)
    			{
    				Value1 = Double.parseDouble(textFieldDisplay.getText());
    				operation = ADDITION;
    			}
    		}
     
    		// Add the methods that will be called when these buttons are pressed
    		ActionListener plusSignListener = new PlusSignListener();
    		buttonPlus.addActionListener(plusSignListener);
     
    		ActionListener equalSignListener = new EqualSignListener();
    		buttonEqual.addActionListener(equalSignListener);
     
    	}
    }
    // called when a subtraction sign '-' is pressed
    		class SubtractionSignListener implements ActionListener {
    			public void actionPerformed(ActionEvent event)
    			{
    				Value1 = Double.parseDouble(textFieldDisplay.getText());
    				operation = Subtraction;
    			}
    		}
     
    		// Add the methods that will be called when these buttons are pressed
    		ActionListener subtractionSignListener = new SubtractionSignListener();
    		buttonPlus.addActionListener(subtractionSignListener);
     
    		ActionListener equalSignListener = new EqualSignListener();
    		buttonEqual.addActionListener(equalSignListener);
             }
    )
    // called when a division sign '/' is pressed
    		class DivisionSignListener implements ActionListener {
    			public void actionPerformed(ActionEvent event)
    			{
    				Value1 = Double.parseDouble(textFieldDisplay.getText());
    				operation = DIVISION;
    			}
    		}
     
    		// Add the methods that will be called when these buttons are pressed
    		ActionListener divisionSignListener = new DivisionSignListener();
    		buttonPlus.addActionListener(plusSignListener);
     
    		ActionListener equalSignListener = new EqualSignListener();
    		buttonEqual.addActionListener(equalSignListener);
              }
    ) 
    // called when a plus sign '*' is pressed
    		class MulitplicationSignListener implements ActionListener {
    			public void actionPerformed(ActionEvent event)
    			{
    				Value1 = Double.parseDouble(textFieldDisplay.getText());
    				operation = Multiplication;
    			}
    		}
     
    		// Add the methods that will be called when these buttons are pressed
    		ActionListener multiplicationSignListener = new MultiplicationSignListener();
    		buttonPlus.addActionListener(plusSignListener);
     
    		ActionListener equalSignListener = new EqualSignListener();
    		buttonEqual.addActionListener(equalSignListener);
     
    	}
    }

  7. #7
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    Default Re: Problem understanding Java code modification

    Please enclose your posted code in code tags to preserve formatting. Use the # icon above the input area to generate the code tags. Not the # character. See: BB Code List - Java Forums
      int 1 = 1; // sample code in tags

    Does the code execute the way you want it to?
    Last edited by Norm; June 26th, 2011 at 08:04 AM.

  8. #8
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    Default Re: Problem understanding Java code modification

    class, interface, or enum expected
    ActionListener subtractionSignListener = new SubtractionSignListener();

    Getting the above mentioned errors on numerous lines,program won't compile

  9. #9
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    Default Re: Problem understanding Java code modification

    Hope you backed up the working version.
    I would suggest that you start with the working version and make small changes to it, compile it to test for errors and then make some more small changes, compile it, etc.

    Your copying and pasting over and over picked up too much code and is FULL of errors. Go back to the working version and try again.

  10. #10
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    Default Re: Problem understanding Java code modification

    Instead of copying and pasting the similar sections. Should i just re type them? Also section that began with // called when a '-' sign is pressed.. is that correct or close? Confused on how to approach this

  11. #11
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    Default Re: Problem understanding Java code modification

    Copy and pasting can be faster but can be a problem if you forget to change it for the new code.

    Sorry, when I searched for "// called when a '-' sign is pressed" it was not found in this post (except in your last post).

  12. #12
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    Default Re: Problem understanding Java code modification

    I was told problem could also be one too many closing braces above error lines( the first error message comes in line 94) where is the extra or mismatched brace..i cannot find it. if I can i think that may solve issues

  13. #13
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    Default Re: Problem understanding Java code modification

    where is the extra or mismatched brace..i cannot find it.
    Many IDEs have tools to find matching {}s. Put the cursor on {, press the keys/icon and the cursor jumps to the matching }.

    Use this tool starting in the middle and work out, making sure that all {s are paired with a matching }

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