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Thread: Simple GUI Error

  1. #1
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    Default Simple GUI Error

    I coded all of this from what the book i'm reading said to do and I don't know what I did wrong. The majority of the code looks fine except for these two errors.

    import java.awt.*;
    import javax.swing.*;
     
    public class LottoMadness extends JFrame {
     
    	//set up row 1
    	JPanel row1 = new JPanel();
    	ButtonGroup option = new ButtonGroup();
    	JCheckBox quickpick = new JCheckBox("Quick Pick", false);
    	JCheckBox personal = new JCheckBox("Personal", true);
    	//set up row 2
    	JPanel row2 = new JPanel();
    	JLabel numbersLabel = new JLabel("Your picks: ", JLabel.RIGHT);
    	JTextField[] numbers = new JTextField[6];
    	JLabel winnersLabel = new JLabel("Winners:", JLabel.RIGHT);
    	JTextField[] winners = new JTextField[6];
    	//set up row 3
    	JPanel row3 = new JPanel();
    	JButton stop = new JButton("Stop");
    	JButton play = new JButton("Play");
    	JButton reset = new JButton("Reset");
    	//set up row 4
    	JPanel row4 = new JPanel();
    	JLabel got3Label = new JLabel("3 of 6", JLabel.RIGHT);
    	JTextField got3 = new JTextField("0");
    	JLabel got4Label = new JLabel("4 of 6", JLabel.RIGHT);
    	JTextField got4 = new JTextField("0");
    	JLabel got5Label = new JLabel("5 of 6", JLabel.RIGHT);
    	JTextField got5 = new JTextField("0");
    	JLabel got6Label = new JLabel("6 of 6", JLabel.RIGHT);
    	JTextField got6 = new JTextField("0");
    	JLabel drawingsLabel = new JLabel("Drawings", JLabel.RIGHT);
    	JTextField drawings = new JTextField("0");
    	JLabel yearsLabel = new JLabel("Years: ", JLabel.RIGHT);
    	JTextField years = new JTextField();
     
    	public LottoMadness() {
    		super("Lotto Madness");
    		setLookAndFeel();
    		setSize(550,400);
    		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    		GridLayout layout = new GridLayout(5, 1, 10, 10);
    		setLayout(layout);
     
    		FlowLayout layout1 = new FlowLayout(FlowLayout.CENTER, 10, 10);
    		option.add(quickpick);
    		option.add(personal);
    		row1.setLayout(layout1);
    		row1.add(quickpick);
    		row1.add(personal);
    		add(row1);
     
    		GridLayout layout2 = new GridLayout(2, 7, 10, 10);
    		row2.setLayout(layout2);
    		row2.add(numbersLabel);
    		for (int i = 0; i < 6; i++){
    			numbers[i] = new JTextField();
    			row2.add(numbers[1]);
    		}
    		row2.add(winnersLabel);
    		for (int i = 0; i < 6; i++){
    			winners[i] = new JTextField();
    			winners[i].setEditable(false);
    			row2.add(winners[i]);
    		}
    		add(row2);
     
    		FlowLayout layout3 = new FlowLayout(FlowLayout.CENTER, 10, 10);
    		row3.setLayout(layout3);
    		stop.setEnabled(false);
    		row3.add(stop);
    		row3.add(play);
    		row3.add(reset);
    		add(row3);
     
    		GridLayout layout4 = new GridLayout(2, 3, 20, 10);
    		row4.setLayout(layout4);
    		row4.add(got3Label);
    		got3.setEditable(false);
    		row4.add(got3);
    		row4.add(got4Label);
    		got4.setEditable(false);
    		row4.add(got4);
    		row4.add(got5Label);
    		got5.setEditable(false);
    		row4.add(got5);
    		row4.add(got6Label);
    		got6.setEditable(false);
    		row4.add(got6);
    		drawings.setEditable(false);
    		row4.add(drawings);
    		row4.add(yearsLabel);
    		years.setEditable(false);
    		row4.add(years);
    		add(row4);
     
    		setVisible(true);
    	}
     
    	private void setLookAndFeel() {
    		try {
    			UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
    		} catch (Exception exc) {
    			//ignore error
    		}
    	}
     
    	public static void main(String[] args){
    		LottoMadness frame = new LottoMadness();
    	}
     
    }

    The errors are:

    1. Where I define the class (public class LottoMadness extends JFrame {) it warns me "The serializable class LottoMadness does not declare a static final serialVersionUID of type long.

    2. In the main method it says the variables JFrame and frame are not used.

    Help is appreciated!


  2. #2
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    Default Re: Simple GUI Error

    What book are you using? I ask, because the main() method is teaching bad habits and is not technically correct. Will it work? Yes, but it's bad form for later. (Saw something similar online, is it Sam's Teach Yourself Java in 24 Hours? If so, which edition do you have?)

    What you posted are warnings, not errors. The code you posted will run fine with those warnings. I didn't run the code, but I'm assuming there are no other errors and therefore that you've dong nothing wrong. If you're bothered by them, you can configure the IDE (if you're using one) and the compiler to suppress warnings.

  3. #3
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    Default Re: Simple GUI Error

    Yes, that is the book i'm using (7th edition). And you said it should work but it doesn't. Here's what the console says :

    Exception in thread "main" java.lang.NullPointerException
    at java.awt.Container.addImpl(Unknown Source)
    at java.awt.Container.add(Unknown Source)
    at LottoMadness.<init>(LottoMadness.java:58)
    at LottoMadness.main(LottoMadness.java:109)

  4. #4
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    Default Re: Simple GUI Error

    That error is not related to the warnings you posted. I assumed there were no other errors, and I was wrong. You have a typo in the line (#58 by my count):

    row2.add( numbers[1] );

    See if you can find it.

  5. #5
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    Default Re: Simple GUI Error

    O! It's supposed to be [i]. Thanks!

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    Default Re: Simple GUI Error

    You're welcome.

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