线程“ AWT-EventQueue-0”中的异常java.lang.NumberFormatException：对于输入字符串：“ null”

Question

package Unit2Exam;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Unit2Exam {

    static int r;
    static int g;
    static int b;
    static int rb;
    static int rg;
    static int on;
    static int rr;
    static int i;
    public static JTextField field1;
    public static JTextField field2;
    public static JTextField field3;

    public static void main(String[] args) {
        //This is my constructor for the Math class, it allows me to import methods from that class
        //final Math a = new Math();
        final Unit2Exam Calculator = new Unit2Exam();

        //Makes a font
        Font font = new Font("Verdana", Font.PLAIN,  12);

        GridBagConstraints grid = new GridBagConstraints();
        //This creates the JFRAMES
        JFrame frame = new JFrame("Free Fall Application");
        //This sets the title
        JPanel panel = new JPanel(new GridBagLayout());
        //makes and adds the panel
        frame.add(panel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        grid.fill = GridBagConstraints.BOTH;

        JFrame colors = new JFrame("Colors");
        JPanel colorPanel = new JPanel(new GridBagLayout());
        colors.add(colorPanel);
        colors.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        grid.fill = GridBagConstraints.BOTH;

        //causes the jbuttons to fill the borders (to make it look better)
        grid.weightx = 1;
        grid.weighty = 1;
        // frame.setSize(new Dimension(200, 200));
        frame.setResizable(false);
        colors.setResizable(false);
        colors.setVisible(true);
        colorPanel.setVisible(true);
        frame.setVisible(true);
        panel.setVisible(true);

        //This is where I implement all of the J stuff (i.e. Buttons, Textfields, and JLabels)
        JLabel title = new JLabel("Jonathan Kipper");
        JLabel label1 = new JLabel("Initial Velocity (m/s):");
        JLabel label2 = new JLabel("Time (Seconds):");
        JLabel label3 = new JLabel("Distance (meters):");
        JTextField field1 = new JTextField(6);
        JTextField field2 = new JTextField(6);
        JTextField field3 = new JTextField(6);
        JButton button1 = new JButton("Calculate");
        JButton button2 = new JButton("Clear");
        JButton colorButton = new JButton();

        grid.gridx = 0;
        grid.gridy = 0;
        panel.add(title, grid);
        title.setVisible(true);
        title.setFont(font);

        grid.gridx = 0;
        grid.gridy = 1;
        panel.add(label1, grid);
        label1.setVisible(true);
        label1.setFont(font);

        grid.gridx = 0;
        grid.gridy = 2;
        panel.add(label2, grid);
        label2.setVisible(true);
        label2.setFont(font);

        grid.gridx = 0;
        grid.gridy = 3;
        panel.add(label3, grid);
        label3.setVisible(true);
        label3.setFont(font);

        grid.gridx = 1;
        grid.gridy = 1;
        panel.add(field1, grid);
        field1.setVisible(true);

        grid.gridx = 1;
        grid.gridy = 2;
        panel.add(field2, grid);
        field2.setVisible(true);

        grid.gridx = 1;
        grid.gridy = 3;
        panel.add(field3, grid);
        field3.setText("");
        field3.setVisible(true);

        grid.gridx = 0;
        grid.gridy = 4;
        panel.add(button1, grid);
        button1.setVisible(true);

        grid.gridx = 1;
        grid.gridy = 4;
        panel.add(button2, grid);
        button2.setVisible(true);
        button2.setFont(font);

        frame.pack();
        Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
        frame.setLocation(dim.width / 2 - frame.getSize().width / 2, dim.height / 2 - frame.getSize().height / 2);
        frame.setSize(250, 150);

        grid.gridx=0;
        grid.gridy=0;
        colorPanel.add(colorButton, grid);
        colorButton.setText("Click to stop colors");
        colorButton.setVisible(true);

        colors.pack();
        Dimension dimz = Toolkit.getDefaultToolkit().getScreenSize();
        colors.setLocation(dimz.width / 3 - frame.getSize().width / 3, dimz.height / 2 - frame.getSize().height / 2);
        colors.setSize(200, 150);

        i=1;
        //Infinite for loop

        button1.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                double zzz = Calculator.distance();
                String za = String.valueOf(zzz);
                field3.setText(za);
            }
        });

        button2.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                field1.setText("");
                field2.setText("");
                field3.setText("");

            }
        });



        colorButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                if (i == 1) {
                    colorButton.setText("Click here to start");
                    i = 0;
                } else if (i == 0) {
                    colorButton.setText("Click here to stop");
                    i = 1;
                }

            }
        });

        on = 0;
        r = 0;
        g = 0;
        b = 0;

        rr = 255;
        rg = 255;
        rb = 255;
        //This is the loop for the color changing
        while (i != 0) {
            //Colors
            Color color = new Color(r, g, b);
            Color rcolor = new Color(rr, rg, rb);

            //Panels
            panel.setBackground(color);
            frame.setBackground(color);

            //Buttons
            button1.setBackground(rcolor);
            button2.setBackground(rcolor);
            colorButton.setBackground(rcolor);

            //Labels
            label1.setForeground(rcolor);
            label2.setForeground(rcolor);
            label3.setForeground(rcolor);
            title.setForeground(rcolor);

            //Text fields
            field1.setForeground(rcolor);
            field2.setForeground(rcolor);
            field3.setForeground(rcolor);
            field1.setBackground(color);
            field2.setBackground(color);
            field3.setBackground(color);

            //Sets a slight delay to avoid seizures
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            //Goes through the different colors
            if (on == 0) {
                if (r == 255) {
                    on = 1;
                } else {
                    r++;
                    rr--;
                }
            } else if (on == 1) {
                if (g == 255) {
                    on = 2;
                } else {
                    g++;
                    rg--;
                }
            } else if (on == 2) {
                if (b == 255) {
                    on = 3;
                } else {
                    b++;
                    rb--;
                }
            } else if (on == 3) {
                if (r == 0) {
                    on = 4;
                } else {
                    r--;
                    rr++;
                }
            } else if (on == 4) {
                if (g == 0) {
                    on = 5;
                } else {
                    g--;
                    rg++;
                }
            } else if (on == 5) {
                if (b == 0) {
                    on = 0;
                } else {
                    b--;
                    rb++;
                }
            }
        }
    }

    public static double distance(){

        String d = field1.getText();
        double velocity = Double.parseDouble(d);
        String dd = field2.getText();
        double time = Double.valueOf(dd);

        double totalDistance = (velocity * time) + (4.9 * (time * time));

        return totalDistance;
    }
}

UPDATE: I can't leave the method as a public static void because it errors out when trying to call it to return a value. I've changed the strings to field.getText(); instead of the String.valueOf(field); It keeps giving me nullpoint errors in the method and when I call the method earlier in the program.

Answer 1

Uhm, you are trying to get the String by

String.valueOf(JTextField)

Thats doing something waaay different from what you want. You can get the Text of the Field by:

e.g. String d = field1.getText();

Edit:

I dont think, Unit2Exam has a purpose, but on your button, you are still using it. First of all, declare distance as static Method:

public static void distance()

Then, replace in your ActionListener

aa.distance()

with

Calculator.distance()

Edit 2:

So, another answer.

First of all, your code is quite messed up, i assume you are new to java. Let me tell you your mistakes:

First of all:

  final Unit2Exam Calculator = new Unit2Exam();

Since you have no constructor, you dont need this. Cut it out.

Second:

The reason, why youre field returns null, is because:

 JTextField field1 = new JTextField(6);
 JTextField field2 = new JTextField(6);
 JTextField field3 = new JTextField(6);

creates a local Textfield called field1, which has nothing to do with your global JTextField field1, which stays empty for the rest of its life.

Just remove the "JTextField" before each declaration and it should work:

 field1 = new JTextField(6);
 field2 = new JTextField(6);
 field3 = new JTextField(6);

Final result:

  package Unit2Exam;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Unit2Exam {

    static int r;
    static int g;
    static int b;
    static int rb;
    static int rg;
    static int on;
    static int rr;
    static int i;
    public static JTextField field1;
    public static JTextField field2;
    public static JTextField field3;

    public static void main(String[] args) {

        //Makes a font
        Font font = new Font("Verdana", Font.PLAIN,  12);

        GridBagConstraints grid = new GridBagConstraints();
        //This creates the JFRAMES
        JFrame frame = new JFrame("Free Fall Application");
        //This sets the title
        JPanel panel = new JPanel(new GridBagLayout());
        //makes and adds the panel
        frame.add(panel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        grid.fill = GridBagConstraints.BOTH;

        JFrame colors = new JFrame("Colors");
        JPanel colorPanel = new JPanel(new GridBagLayout());
        colors.add(colorPanel);
        colors.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        grid.fill = GridBagConstraints.BOTH;

        //causes the jbuttons to fill the borders (to make it look better)
        grid.weightx = 1;
        grid.weighty = 1;
        // frame.setSize(new Dimension(200, 200));
        frame.setResizable(false);
        colors.setResizable(false);
        colors.setVisible(true);
        colorPanel.setVisible(true);
        frame.setVisible(true);
        panel.setVisible(true);

        //This is where I implement all of the J stuff (i.e. Buttons, Textfields, and JLabels)
        JLabel title = new JLabel("Jonathan Kipper");
        JLabel label1 = new JLabel("Initial Velocity (m/s):");
        JLabel label2 = new JLabel("Time (Seconds):");
        JLabel label3 = new JLabel("Distance (meters):");
        field1 = new JTextField(6);
       field2 = new JTextField(6);
         field3 = new JTextField(6);
        JButton button1 = new JButton("Calculate");
        JButton button2 = new JButton("Clear");
        JButton colorButton = new JButton();

        grid.gridx = 0;
        grid.gridy = 0;
        panel.add(title, grid);
        title.setVisible(true);
        title.setFont(font);

        grid.gridx = 0;
        grid.gridy = 1;
        panel.add(label1, grid);
        label1.setVisible(true);
        label1.setFont(font);

        grid.gridx = 0;
        grid.gridy = 2;
        panel.add(label2, grid);
        label2.setVisible(true);
        label2.setFont(font);

        grid.gridx = 0;
        grid.gridy = 3;
        panel.add(label3, grid);
        label3.setVisible(true);
        label3.setFont(font);

        grid.gridx = 1;
        grid.gridy = 1;
        panel.add(field1, grid);
        field1.setVisible(true);

        grid.gridx = 1;
        grid.gridy = 2;
        panel.add(field2, grid);
        field2.setVisible(true);

        grid.gridx = 1;
        grid.gridy = 3;
        panel.add(field3, grid);
        field3.setText("");
        field3.setVisible(true);

        grid.gridx = 0;
        grid.gridy = 4;
        panel.add(button1, grid);
        button1.setVisible(true);

        grid.gridx = 1;
        grid.gridy = 4;
        panel.add(button2, grid);
        button2.setVisible(true);
        button2.setFont(font);

        frame.pack();
        Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
        frame.setLocation(dim.width / 2 - frame.getSize().width / 2, dim.height / 2 - frame.getSize().height / 2);
        frame.setSize(250, 150);

        grid.gridx=0;
        grid.gridy=0;
        colorPanel.add(colorButton, grid);
        colorButton.setText("Click to stop colors");
        colorButton.setVisible(true);

        colors.pack();
        Dimension dimz = Toolkit.getDefaultToolkit().getScreenSize();
        colors.setLocation(dimz.width / 3 - frame.getSize().width / 3, dimz.height / 2 - frame.getSize().height / 2);
        colors.setSize(200, 150);

        i=1;
        //Infinite for loop

        button1.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                double zzz = Unit2Exam.distance();
                String za = String.valueOf(zzz);
                field3.setText(za);
            }
        });

        button2.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                field1.setText("");
                field2.setText("");
                field3.setText("");

            }
        });



        colorButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                if (i == 1) {
                    colorButton.setText("Click here to start");
                    i = 0;
                } else if (i == 0) {
                    colorButton.setText("Click here to stop");
                    i = 1;
                }

            }
        });

        on = 0;
        r = 0;
        g = 0;
        b = 0;

        rr = 255;
        rg = 255;
        rb = 255;
        //This is the loop for the color changing
        while (i != 0) {
            //Colors
            Color color = new Color(r, g, b);
            Color rcolor = new Color(rr, rg, rb);

            //Panels
            panel.setBackground(color);
            frame.setBackground(color);

            //Buttons
            button1.setBackground(rcolor);
            button2.setBackground(rcolor);
            colorButton.setBackground(rcolor);

            //Labels
            label1.setForeground(rcolor);
            label2.setForeground(rcolor);
            label3.setForeground(rcolor);
            title.setForeground(rcolor);

            //Text fields
            field1.setForeground(rcolor);
            field2.setForeground(rcolor);
            field3.setForeground(rcolor);
            field1.setBackground(color);
            field2.setBackground(color);
            field3.setBackground(color);

            //Sets a slight delay to avoid seizures
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            //Goes through the different colors
            if (on == 0) {
                if (r == 255) {
                    on = 1;
                } else {
                    r++;
                    rr--;
                }
            } else if (on == 1) {
                if (g == 255) {
                    on = 2;
                } else {
                    g++;
                    rg--;
                }
            } else if (on == 2) {
                if (b == 255) {
                    on = 3;
                } else {
                    b++;
                    rb--;
                }
            } else if (on == 3) {
                if (r == 0) {
                    on = 4;
                } else {
                    r--;
                    rr++;
                }
            } else if (on == 4) {
                if (g == 0) {
                    on = 5;
                } else {
                    g--;
                    rg++;
                }
            } else if (on == 5) {
                if (b == 0) {
                    on = 0;
                } else {
                    b--;
                    rb++;
                }
            }
        }
    }

    public static double distance(){

        String d = field1.getText();
        double velocity = Double.parseDouble(d);
        String dd = field2.getText();
        double time = Double.valueOf(dd);

        double totalDistance = (velocity * time) + (4.9 * (time * time));

        return totalDistance;
    }

Answer 2

I change it to

public double distance() {

    String d = field1.getText();
    double velocity = Double.parseDouble(d);
    String dd = field2.getText();
    double time = Double.valueOf(dd);

    double totalDistance = (velocity * time) + (4.9 * (time * time));

    return totalDistance;
}

However I'm still getting a null pointer exception. It changed the error slightly however. It's saying on line 273, which is the: String d = field1.getText(); is an issue.