我正在尝试使用getText()方法将用户输入存储到全局静态变量中。
userinput是JTextField，在createContentPane()
我创建了一个访问器方法getText()来从JTextField获取用户输入并将其存储在名为words的静态变量中，但是我收到一条错误消息。
package Windows;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Ceaser_Cipher extends JFrame implements ActionListener
{
private static JLabel titleLabel;
private static JTextField userinput;
private static JTextArea resultTA;
private static JButton runButton, homeButton;
private static String words;
private static int key = 5;
private static String cipherd;
private static String decipherd;
public static void createAndShowGUI()
{
JFrame.setDefaultLookAndFeelDecorated(true);
JFrame frame = new JFrame("[=] Ceaser_Cipher [=]");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(500, 600);
frame.setVisible(true);
Ceaser_Cipher GUI = new Ceaser_Cipher();
frame.setContentPane(GUI.createContentPane());
}
public JPanel createContentPane()
{
JPanel totalGUI = new JPanel();
totalGUI.setLayout(null);
JPanel titlepanel = new JPanel();
titlepanel.setBackground(Color.pink);
titlepanel.setLayout(null);
titlepanel.setLocation(0, 0);
titlepanel.setSize(500, 150);
totalGUI.add(titlepanel);
titleLabel = new JLabel("WELCOME to Ceaser's Cipher!!!!");
titleLabel.setLocation(0, 0);
titleLabel.setSize(500, 140);
titleLabel.setHorizontalAlignment(0);
titlepanel.add(titleLabel);
JPanel textpanel = new JPanel();
textpanel.setBackground(Color.red);
textpanel.setLayout(null);
textpanel.setLocation(0, 150);
textpanel.setSize(500, 150);
totalGUI.add(textpanel);
userinput = new JTextField("Enter the word you want to ENCRYPT");
userinput.setHorizontalAlignment(2);
userinput.setLocation(100, 0);
userinput.setSize(300, 140);
textpanel.add(userinput);
JPanel resultpanel = new JPanel();
resultpanel.setBackground(Color.yellow);
resultpanel.setLayout(null);
resultpanel.setLocation(0, 300);
resultpanel.setSize(500, 150);
totalGUI.add(resultpanel);
resultTA = new JTextArea();
resultTA.setLocation(50, 0);
resultTA.setSize(400, 140);
resultpanel.add(resultTA);
JPanel buttonpanel = new JPanel();
buttonpanel.setBackground(Color.green);
buttonpanel.setLayout(null);
buttonpanel.setLocation(0, 450);
buttonpanel.setSize(500, 200);
totalGUI.add(buttonpanel);
runButton = new JButton("RUN!");
runButton.setLocation(200, 10);
runButton.setSize(100, 30);
runButton.addActionListener(this);
buttonpanel.add(runButton);
homeButton = new JButton("HOME!");
homeButton.setLocation(200, 50);
homeButton.setSize(100, 30);
homeButton.addActionListener(this);
buttonpanel.add(homeButton);
totalGUI.setOpaque(true);
return totalGUI;
}
public void actionPerformed(ActionEvent evt)
{
Object src = evt.getSource();
if (src == runButton)
{
resultTA.setText("\n" + "The ENCRYPTION key generated is " + key + "\n" + "ENCRYPTED text is " + cipherd
+ "\n" + "DECRYPTED text is " + decipherd);
}
if (src == homeButton)
{
}
}
public static void main(String[] args)
{
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
createAndShowGUI();
}
});
}
key = random();
words = getText();
cipherd = encrpt(words, key);
decipherd = decrpt(cipherd, key);
}
private static String getText()
{
String word = userinput.getText();
return word;
}
public static String encrpt(String text, int key)
{
//Array containing all the alphabetical characters.
char alphabets [] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
'U', 'V', 'W', 'X', 'Y', 'Z'};
//Array where the user's String will be inserted into and replaced with the ENCRYPTED characters.
char plain [] = words.toUpperCase().toCharArray();
//ENCRYPTION loop here, replaces the characters in the users String with the shifted alphabets based on the ENCRYPTION key.
for (int i = 0; i < plain.length; i++)
{
for (int j = 0; j < alphabets.length; j++)
{
if(plain[i] == alphabets[j])
{
plain[i] = alphabets[(j + key) % 26];
break;
}
}
}
String cipher = String.valueOf(plain);
return cipher;
}
public static String decrpt(String text, int key)
{
//Array containing all the alphabetical characters.
char alphabets [] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
'U', 'V', 'W', 'X', 'Y', 'Z'};
char plain [] = words.toUpperCase().toCharArray();
char cipherd [] = new char[100];
//DECRYPTION loop here, gets the ENCRYPTED characters and replaces them with the original alphabets by reversing the ENCRYPTION key.
for (int i = 0; i < plain.length; i++)
{
for (int j = 0; j < alphabets.length; j++)
{
if(plain[i] == alphabets[j])
{
cipherd[i] = alphabets[(j - key + 26) % 26];
break;
}
}
}
String decipher = String.valueOf(cipherd);
return decipher;
}
public static int random()
{
//Random object created here.
Random ran = new Random();
//Random number between 1-3 is generated here.
key = ran.nextInt(9) + 1;
return key;
}
}
答案 0 :(得分：2)
调用JTextField时userinput getText尚未初始化（因为它将在EDT中初始化），导致NullPointerException在这一行
String word = userinput.getText();
创建用户界面并检索EDT。
以下是不的列表：
static语言（如Java。OO个变量
JFrame，创建实例并使用null布局），而是使用布局管理器答案 1 :(得分：1)
问题是：
在words = getText();，JTextField实例化之前调用userinput方法。因为，到时为null，您将获得NullPointerException。
答案 2 :(得分：1)
您正在创建错误的框架。如果您已经使该课程扩展了JFrame，那么创建新的JFrame就没有意义了。将班级更改为
public class Ceaser_Cipher extends JFrame implements ActionListener
{
// remove the keyword 'static' from the variables. it's not necessary.
private JLabel titleLabel;
private JTextField userinput;
private JTextArea resultTA;
private JButton runButton, homeButton;
private String words;
private int key = 5;
private String cipherd;
private String decipherd;
// constructor.
public Ceaser_Cipher()
{
// this class extends a JFrame. so you can call it's methods directly
// and you do not need to create the frame again.
super("[=] Ceaser_Cipher [=]");
setCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(500, 600);
// set the content pane to the panel returned by your method.
setContentPane(createContentPane());
// avoid calculations in the main method. you may place them here.
key = random();
words = userInput.getText();
cipherd = encrpt(words, key);
decipherd = decrpt(cipherd, key);
setVisible(true);
}
// Your createContentPane method. it's fine. copy it here.
// Your actionPerformed method is also fine. copy it here.
// And finally the main method.
public static void main(String[] args)
{
// This calls the constructor and everything will be fine.
new Ceaser_Cipher();
}
}