Thread: 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);
        createButtons();
        createTextField();
 
    }
 
    public void createTextField() {
        JPanel northPanel = new JPanel();
        northPanel.setLayout(new BorderLayout());
 
        textField = new JTextField(29);
        textField.setEditable(true);
 
        northPanel.add(textField);
 
 
        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;
                    }
                }
 
                textField.setText(input);
 
 
            }
        }
        ButtonListener thelistener = new ButtonListener();
 
        button.addActionListener(thelistener);
        return button;
    }
}