如何从TextField获取用户输入并将其转换为Double？

Question

I'm using Eclipse to build a calculator and I am having trouble because I need to have 2 values entered by the user. Here is my code for the run class.

import display.Gui;

public class Main {

public static void main(String argsp[]) {

    Gui window = new Gui();
    double a = 0, b = 0, c = 0;
    String operator;
    boolean calculate = true;

    window.setVisible(true);
    window.setSize(500, 400);
    window.setResizable(false);
    window.setLocationRelativeTo(null);

    while (calculate) {
        window.textArea_1.append("Enter an equation.\n");
        a = Double.parseDouble(window.textField.getText());
        operator = window.textField.getText();
        b = Double.parseDouble(window.textField.getText());

        if (operator.contains("+"))
            c = a + b;

        if (operator.contains("-"))
            c = a - b;

        if (operator.contains("*"))
            c = a * b;

        if (operator.contains("/"))
            c = a / b;

        if (operator.contains("x^2"))
            c = a * a;

        if (operator.contains("sqrt"))
            c = Math.sqrt(a);

        if (operator.contains("%"))
            c = a / 100;

        window.textArea.append("" + c + "\n");
        window.textArea.append("");
        window.textArea.append("Would you like to make another calculation? [Yes/No]\n");

        String calculation = window.textField.getText();

        try {
        if (calculation.equalsIgnoreCase("Yes"))
            calculate = true;

        if (calculation.equalsIgnoreCase("No"))
            calculate = false;
        } catch (Exception e) {
            window.textArea_1.append("Please enter yes or no");
        }

    }
}

}

and here is my class for the JFrame:

import java.awt.Dimension;
import java.awt.EventQueue;

import javax.swing.JFrame;
import java.awt.BorderLayout;
import javax.swing.JTextField;
import javax.swing.JTextArea;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class Gui extends JFrame {

public JTextArea textArea, textArea_1;
public JTextField textField;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                Gui frame = new Gui();
                frame.setVisible(false);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the frame.
 */
public Gui() {
    setBounds(100, 100, 450, 300);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    getContentPane().setLayout(new BorderLayout(0, 0));

    textField = new JTextField();
    textField.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent Ev) {
            textArea.append(textField.getText() + "\n");
            textField.setText("");
        }
    });
    textField.requestFocus();
    getContentPane().add(textField, BorderLayout.SOUTH);
    textField.setColumns(10);

    textArea = new JTextArea();
    textArea.setEditable(false);
    textArea.setPreferredSize(new Dimension(215, 200));
    getContentPane().add(textArea, BorderLayout.WEST);

    textArea_1 = new JTextArea();
    textArea_1.setEditable(false);
    textArea_1.setPreferredSize(new Dimension(215, 200));
    getContentPane().add(textArea_1, BorderLayout.EAST);

}

i tried using Double.parseDouble(window.textField.getText());

but that didn't work. How can I make it work? Thanks in advance.

Answer 1

First of all I think there are some issues with your design of the program.Why not use events (button clicks, keystrokes pressed etc) to trigger the calculations? I do not see the benefit of the while loop in this program.

Also, as some folks have already pointed out, your code is reading and parsing values from textfield even before user input. That surely will yield an invalid results.

Try something like (not tested):

calcButton = new JButton("Calculate");
calcButton.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent Ev) {
        actionCalc();
    }
});


public void actionCalc(){
    // get the string
    // validate string (check for empty string etc)
    // parse to Double
    Double val = Double.parseDouble(window.textField.getText());
    ...
}

Answer 2

You are requesting text from the TextField without actually checking if the text is there. If you would like to loop this way you must first see if there is text entered, then assign the input to the double. I would recommend a different strategy though.

Your logic of using a loop here is not the best in my opinion. If you must read both numbers from the TextField I would actually add a KeyListener and await for the enter key. Something like

PSEUDO-CODE

...
// global vals
double a = Null;
double b = Null;
public void keyPressed(KeyEvent e) {
    if (e.getKeyCode() == KeyEvent.VK_ENTER) {
        if (!window.textField.getText().equals("")) {
            // check if input is a legal double value
            // notify user that you recieved the first number
            // and request the next input.
            // once both inputs have been entered do your calculation and 
            // output the result. The program will continue to respond to key triggers.
        }
    }
}

HELPFUL LINKS

Here is some more info on KeyListeners: http://docs.oracle.com/javase/tutorial/uiswing/events/keylistener.html

Here is a link on TextField and how to use them: http://docs.oracle.com/javase/tutorial/uiswing/components/textfield.html

Answer 3

这是你如何做到的：

double value=Double.parseDouble(jtextfield-name.getText());

Answer 4

You can directly use:

Double.valueOf("Pass your string here");

It is a static method that returns double value of whatever being given in the arguments.