Exception in thread "AWT-Eventqueue-0" java.lang.NumberFormatException: Für Eingabestring: "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: Ich kann die Methode als public static void verlassen, weil es Fehler, wenn zu versuchen, Rufen Sie es auf, um einen Wert zurückzugeben. Ich habe die Zeichenfolgen in field.getText() geändert; anstelle von String.valueOf (Feld); Es gibt mir Nullpunkt Fehler in der Methode und wenn ich die Methode früher im Programm aufrufen.

Answer 1

Uhm, Sie versuchen, den String von

String.valueOf(JTextField) 

Das ist etwas zu tun waaay anders zu bekommen, was Sie wollen. Sie können den Text des Feldes erhalten:

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

Edit:

Ich denke nicht, Unit2Exam einen Zweck hat, aber auf dem Knopf, verwenden Sie es immer noch. Zunächst einmal erklärt Abstand als statische Methode:

public static void distance() 

Ersetzen Sie dann in Ihrer Action

aa.distance() 

mit

Calculator.distance() 

Edit 2:

Also, eine andere Antwort.

Zunächst einmal ist Ihr Code ziemlich durcheinander, ich nehme an, Sie sind neu in Java. Lassen Sie mich Ihnen sagen, Ihre Fehler:

Zu allererst:

final Unit2Exam Calculator = new Unit2Exam(); 

Da Sie keinen Konstruktor haben, können Sie diese nicht benötigen. Schneide es aus.

Zweitens:

Der Grund, warum youre Feld null zurückgibt, ist da:

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

ein field1 genannt lokalen Textfeld erstellt, die nichts mit Ihrem global zu tun hat JTextField field1 , die für den Rest ihres Lebens leer bleibt.

Entfernen Sie einfach die "JTextField" vor jeder Erklärung und es sollte funktionieren:

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

Endergebnis:

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

ich es ändern zu

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; 
} 

aber ich bin Immer noch eine Nullzeigerausnahme. Es änderte sich jedoch der Fehler leicht. Es heißt in Zeile 273: String d = field1.getText(); ist ein Problem.