Parsing multiple doubles from one JTextField

Question

I'm pretty sure I've looked at most of the questions related to this issue, but they all use multiple text fields, one listener per button, or something like that. I'm trying to get multiple double inputs from one text field, where a first variable is set to the initial text and a second variable is set to the second text. So if someone enters 1 + 4, the first variable is set to 1, the + clears the text field, and the second variable is set to 4. This is a first write up so there might be a lot of unnecessary things.

EDIT: Might've been unclear here, what I want to happen is the user enters (for 1 + 4), click button 1 setting the text field to 1 and setting the first variable to 1, then click the + button which clears the text field, then click the 4 button setting the text field to 4 and setting the second variable to 4, then click the equals button, and the result is based off the operator clicked. It's not entered all as one string.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

class GUICalculator extends JFrame implements ActionListener {

    private static final int WIDTH = 300;
    private static final int HEIGHT = 300;
    private JTextField displayField;
    private static final String[] NUMBERS = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "+", "-", "*", "/", "C", "=", "."};
    private static final Set<String> OPERATORS = new HashSet<>(Arrays.asList("+", "-", "*", "/", "C", "="));
    private double n1, n2, result;

    public GUICalculator() {
        super("Calculator");
        setLayout(new BorderLayout());
        setSize(WIDTH, HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new FlowLayout());
        displayField = new JTextField();
        displayField.setEditable(false);
        add(displayField, BorderLayout.NORTH);
        add(buttonPanel);

        for (String number : NUMBERS) {
            JButton buttons = new JButton(number);
            buttons.addActionListener(this);
            buttonPanel.add(buttons);
        }
    }

    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();

        for (String number : NUMBERS) {
            if (command.equals(number) && !OPERATORS.contains(command)) {
                displayField.setText(displayField.getText() + command);
                n1 = Double.parseDouble(displayField.getText());
            }

            //n2 = Double.parseDouble(displayField.getText());

            switch (command) {
                case "+":
                    result = n1 + n2;
                    displayField.setText("");
                case "-":
                    result = n1 - n2;
                    displayField.setText("");
                case "*":
                    result = n1 * n2;
                    displayField.setText("");
                case "/":
                    try {
                        if (n2 == 0)
                            throw new DivisionByZeroException();
                        result = n1 / n2;
                    } catch (DivisionByZeroException f) {
                        f.getMessage();
                        displayField.setText("");
                        break;
                    }
                case "=":
                    displayField.setText(Double.toString(result));
                    break;
                case "C":
                    displayField.setText("");
            }
        }
    }

    public static void main(String[] args) {
        GUICalculator gc = new GUICalculator();
        gc.setVisible(true);
    }
}

The commented line is what I want to go in, but I have no idea where to put it.

See [this answer](http://stackoverflow.com/a/7441804/418556) for working source that uses [`ScriptEngine`](http://docs.oracle.com/javase/8/docs/api/javax/script/ScriptEngine.html) to evaluate the expression. — Andrew Thompson, Oct 06 '14 at 07:36

score 1 · Answer 1 · edited Oct 06 '14 at 07:19

The problem is that Double.parseDouble attempts to parse the entire String, while you are trying to read the String as a set of tokens. This calls for the implementation of an expression parser. Your code already looks a bit like a parser, but needs a way to tokenize the String.

You could take a look at explanations such as this tutorial.

One extra remark: please terminate your case code blocks with a break-statement. If your code were to match a +, it would perform the operations in all of the casess. So, writing 1 + 2 would still yield the result of 1 / 2 and perform the action for an =, because that case does have a break statement. For more information see Oracle info on the switch statement.

Parsing multiple doubles from one JTextField

1 Answers1