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Thread: Calculator Throw Error

  1. #1
    Junior Member
    Join Date
    Jan 2011
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    Default Calculator Throw Error

    I'm working on creating a Calculator. The code is not finished yet but I'm getting an error already at a part I need to work in order to continue building the program.

    I can type in numbers fine, and when I use the addition button the first time it works. However, I'm trying to make it so when I input a number then press + then input another number and press + or = it will display the answer in the textfield. At this point if I try to press the + button twice it will give me this error:

    Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: "987561+"
    at sun.misc.FloatingDecimal.readJavaFormatString(Floa tingDecimal.java:1224)
    at java.lang.Double.parseDouble(Double.java:510)
    at P18_10.Calculator$1ButtonListener.actionPerformed( Calculator.java:117)

    Line 117 in Calculator.java is:
    inputnumber = Double.parseDouble(input);

    Why would it have a problem converting a double to a String?

    Here is my code so far:

    import java.awt.BorderLayout;
    import java.awt.event.ActionListener;
    import java.awt.event.ActionEvent;
    import javax.swing.JFrame;
    import javax.swing.JButton;
    import javax.swing.JPanel;
    import javax.swing.JTextField;
    import java.awt.GridLayout;
    public class Calculator extends JFrame {
        private JPanel ColorPanel;
        private static final int FRAME_WIDTH = 300;
        private static final int FRAME_HEIGHT = 300;
        private ActionListener listener;
        private JTextField textField;
        double inputnumber = 0;
        String input = "0";
        double actionnumber = 0;
        double answer = 0;
        String action = null;
        String operation = "=";
        public Calculator() {
            setSize(FRAME_WIDTH, FRAME_HEIGHT);
            ColorPanel = new JPanel();
            add(ColorPanel, BorderLayout.CENTER);
        public void createTextField() {
            JPanel northPanel = new JPanel();
            northPanel.setLayout(new BorderLayout());
            textField = new JTextField(29);
            add(northPanel, BorderLayout.NORTH);
        public void createButtons() {
            JPanel southPanel = new JPanel();
            southPanel.setLayout(new GridLayout(4, 3));
            southPanel.add(makeButton("7", "7"));
            southPanel.add(makeButton("8", "8"));
            southPanel.add(makeButton("9", "9"));
            southPanel.add(makeButton("4", "4"));
            southPanel.add(makeButton("5", "5"));
            southPanel.add(makeButton("6", "6"));
            southPanel.add(makeButton("1", "1"));
            southPanel.add(makeButton("2", "2"));
            southPanel.add(makeButton("3", "3"));
            southPanel.add(makeButton("0", "0"));
            southPanel.add(makeButton(".", "."));
            southPanel.add(makeButton("CE", "CE"));
            southPanel.add(makeButton("+", "+"));
            southPanel.add(makeButton("-", "-"));
            southPanel.add(makeButton("X", "X"));
            southPanel.add(makeButton("/", "/"));
            add(southPanel, BorderLayout.CENTER);
        public JButton makeButton(String label, final String action) {
            JButton button = new JButton(label);
            class ButtonListener implements ActionListener {
                public void actionPerformed(ActionEvent event) {
                    if (action.equals("=")) {
                        inputnumber = Double.parseDouble(input);
                        if (operation.equals("+")) {
                            answer = answer + inputnumber;
                            inputnumber = answer;
                            input = Double.toString(inputnumber);
                        if (input.equals("0")) {
                            input = action;
                        } else {
                            operation = "=";
                        input += action;
                        System.out.println("We are going to Add " + inputnumber + " To the Next Number");
                    } else if (action.equals("+")) {
                        inputnumber = Double.parseDouble(input);
                        if (operation.equals("+")) {
                            answer = answer + inputnumber;
                            inputnumber = answer;
                            input = Double.toString(inputnumber);
                        if (input.equals("0")) {
                            input = action;
                        } else {
                            operation = "+";
                            input += action;
                            System.out.println("We are going to Add " + inputnumber + " To the Next Number");
                    } else {
                        if (input.equals("0")) {
                            input = action;
                        } else {
                            input += action;
            ButtonListener thelistener = new ButtonListener();
            return button;

  2. #2
    Super Moderator helloworld922's Avatar
    Join Date
    Jun 2009
    Thanked 619 Times in 561 Posts
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    Default Re: Calculator Throw Error

    The problem is that you're parsing the whole string (including the plus). For example, "123+" is not a number, and Java is telling you that. What you could do is remove that last character, then you'd be left with "123", which Java can parse into a double.

    if(input.charAt(input.length()-1) == '+')
        inputnumber = Double.parseDouble(input.substring(0,input.length() - 1)); // untested code, should work though
        inputNumber = Double.parseDouble(input);

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