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Thread: What am I doing wrong?

  1. #1
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    Question What am I doing wrong?

    Hi, can someone help we please?
    I need to write a temperature-conversion application that converts from fahrenheit to celsius. The temperature should be entered from the keyboard(via a jtextfield). And a label should be used to display the converted temperature.

    This is mine code:

    import java.awt.FlowLayout;
    import java.awt.GridLayout;
    import javax.swing.JTextField;
    import javax.swing.JLabel;
    import javax.swing.JFrame;
    import javax.swing.JPanel;
     
     
    public class Conversion extends JFrame{
        private final JTextField fField;
        private final JLabel cLabel;
        private final JLabel label;
        private final JLabel fLabel;
        private final JPanel panel;
        private final JPanel fPanel;
        private final JPanel cPanel;
     
     
        public Conversion(){
            super("Temperature Conversion");
            setLayout(new FlowLayout());
     
            panel = new JPanel(new GridLayout(2,1));
            fPanel = new JPanel(new GridLayout(1,2));
            cPanel = new JPanel(new GridLayout(1,2));
     
            fLabel = new JLabel("Enter fahrenheit: ");
            fField = new JTextField(5);
            fPanel.add(fLabel);
            fPanel.add(fField);
     
            int f = Integer.parseInt(fField.getText());
            int c = 5/9 * (f - 32);
     
            label = new JLabel();
            label.setText(Integer.toString(c));
            cLabel = new JLabel("Celsius: ");
            cPanel.add(cLabel);
            cPanel.add(label);
     
            panel.add(fPanel);
            panel.add(cPanel);
     
            add(panel);
        }
    }

    This is the error i'm getting:
    Exception in thread "main" java.lang.NumberFormatException: For input string: ""
    at java.base/java.lang.NumberFormatException.forInputString(Num berFormatException.java:65)
    at java.base/java.lang.Integer.parseInt(Integer.java:662)
    at java.base/java.lang.Integer.parseInt(Integer.java:770)
    at Conversion.<init>(Conversion.java:32)
    at ConversionTest.main(ConversionTest.java:5)
    C:\Users\Maneesha\AppData\Local\NetBeans\Cache\10. 0\executor-snippets\run.xml:111: The following error occurred while executing this line:
    C:\Users\Maneesha\AppData\Local\NetBeans\Cache\10. 0\executor-snippets\run.xml:68: Java returned: 1

  2. #2
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    Default Re: What am I doing wrong?

    it's still not working

  3. #3
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    Default Re: What am I doing wrong?

    First, all you have provided is the constructor. You also need a static main method as an entry point (or include the rest of your code that creates an instance of the Conversion class).

    You need to set up your Frame properly and add your text field to it. Then display the frame. I recommend you check out the tutorials in my signature on how to use JTextFields. They give some good examples.

    Also, it is considered bad practice to extend JFrame. Best to just create an instance and use that.

    Regards,
    Jim

  4. The Following 2 Users Say Thank You to jim829 For This Useful Post:

    Faerthurin (April 9th, 2019), John Joe (April 9th, 2019)

  5. #4
    Member John Joe's Avatar
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    Default Re: What am I doing wrong?

    fField.getText().toString(); always return empty string, that why you will get exception. If you want to get value from textField, I would suggest you to add a button there . Once the button clicked, get the value and display on JLabel.
    Last edited by John Joe; April 9th, 2019 at 12:34 PM.
    Whatever you are, be a good one

  6. The Following User Says Thank You to John Joe For This Useful Post:

    Faerthurin (April 9th, 2019)

  7. #5
    Super Moderator Norm's Avatar
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    Default Re: What am I doing wrong?

    Using a GUI requires that the code present a window with text fields, etc and then wait for user interaction. The JVM handles user events and will pass control to a listener when a particular event, like a button press, happens.

    The sequence of events would be:
    The program builds and displays the GUI and sets a listener
    and then exit sthe method to wait for user input
    The user enters some data and presses a button
    The JVM sees the button press and calls the listener for the button
    the listener then gets the data that the user entered and processes it.
    If you don't understand my answer, don't ignore it, ask a question.

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