当获取随机数时，我得到java.lang.NullPointerException
我试图为我的Java程序获取一个随机数，但是什么都没有发生，当我运行程序时，我得到了一个Java.lang.NullPointerException。。。这是我得到随机整数的代码部分，之后我将提供完整的代码。提前感谢您的帮助当获取随机数时，我得到java.lang.NullPointerException,java,nullpointerexception,Java,Nullpointerexception,我试图为我的Java程序获取一个随机数，但是什么都没有发生，当我运行程序时，我得到了一个Java.lang.NullPointerException。。。这是我得到随机整数的代码部分，之后我将提供完整的代码。提前感谢您的帮助 try { PrintStream oFile = new PrintStream("Cipher.txt"); //i get the random number right below here...
try {
PrintStream oFile = new PrintStream("Cipher.txt");
//i get the random number right below here...
rot = random.nextInt(5) + 1;
scan = new Scanner(message);
while (scan.hasNext()) {
cipherWord = scan.next();
l = cipherWord.length();
charScan = new Scanner(cipherWord);
for(int i = 0; i < cipherWord.length(); i++){
cipherChar = cipherWord.charAt(i);
if (cipherChar == 'a') {
cipherChar = 'b';
} else if (cipherChar == 'b') {
cipherChar = 'c';
} else if (cipherChar == 'c') {
cipherChar = 'd';
} else if (cipherChar == 'd') {
cipherChar = 'e';
} else if (cipherChar == 'e') {
cipherChar = 'f';
} else if (cipherChar == 'f') {
cipherChar = 'g';
} else if (cipherChar == 'g') {
cipherChar = 'h';
} else if (cipherChar == 'h') {
cipherChar = 'i';
} else if (cipherChar == 'i') {
cipherChar = 'j';
} else if (cipherChar == 'j') {
cipherChar = 'k';
} else if (cipherChar == 'k') {
cipherChar = 'l';
} else if (cipherChar == 'l') {
cipherChar = 'm';
} else if (cipherChar == 'm') {
cipherChar = 'n';
} else if (cipherChar == 'n') {
cipherChar = 'o';
} else if (cipherChar == 'o') {
cipherChar = 'p';
} else if (cipherChar == 'p') {
cipherChar = 'q';
} else if (cipherChar == 'q') {
cipherChar = 'r';
} else if (cipherChar == 'r') {
cipherChar = 's';
} else if (cipherChar == 's') {
cipherChar = 't';
} else if (cipherChar == 't') {
cipherChar = 'u';
} else if (cipherChar == 'u') {
cipherChar = 'v';
} else if (cipherChar == 'v') {
cipherChar = 'w';
} else if (cipherChar == 'w') {
cipherChar = 'x';
} else if (cipherChar == 'x') {
cipherChar = 'y';
} else if (cipherChar == 'y') {
cipherChar = 'z';
} else if (cipherChar == 'z') {
cipherChar = 'a';
}
oFile.print(cipherChar);
}
oFile.print(" ");
}
oFile.close();
scan.close();
charScan.close();
}
catch(Exception ioe) {
System.out.println("\n*** Print to Cipher.txt Error ***\n" + ioe);
}
试试看{
PrintStream of文件=新的PrintStream（“Cipher.txt”）；
//我得到了下面的随机数。。。
rot=随机。nextInt（5）+1；
扫描=新扫描仪（信息）；
while（scan.hasNext（））{
cipherWord=scan.next（）；
l=密码字长度（）；
charScan=新扫描仪（密码字）；
for（int i=0；iimport java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.util.Random;
import javax.swing.*;
import java.io.*;
public class CodeMaker {
public int rot;
public JScrollPane scrollArea;
public Random random;
public File Cipher;
public int l;
public File message;
public char cipherChar;
public String finalCipher;
public Scanner charScan;
public Scanner scan;
public String cipherWord;
public int z;
public int words;
public File cipherFile;
public int n;
public String cipher;
public JPanel panel;
public JButton saveButton;
public JTextArea textArea;
boolean create = true;
private JFrame frame;
public static void main (String[] args) {
CodeMaker gui = new CodeMaker();
gui.start();
}
private void start() {
frame = new JFrame("Project TrenchCoat: Cipher Creator");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setBackground(Color.DARK_GRAY);
makeMenus();
makeContent();
frame.setVisible(true);
frame.setExtendedState(Frame.MAXIMIZED_BOTH);
}
private void makeMenus() {
JMenuBar menuBar;
menuBar = new JMenuBar();
frame.setJMenuBar(menuBar);
JMenu menu;
menu = new JMenu("File");
JMenuItem menuItem = new JMenuItem("New Cipher");
menuItem.addActionListener(new NewListener());
menuItem.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_N,
Event.CTRL_MASK));
menu.add(menuItem);
JMenuItem menuitem = new JMenuItem("Read Cipher");
menuitem.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_R,
Event.CTRL_MASK));
menu.add(menuitem);
menu.addSeparator();
menuItem = new JMenuItem("Exit");
menuItem.addActionListener(new ExitListener());
menuItem.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_Q,
Event.CTRL_MASK));
menu.add(menuItem);
menuBar.add(menu);
JMenu helpMenu = new JMenu("Help");
JMenuItem helpItem = new JMenuItem("Help");
menuItem.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_H,
Event.CTRL_MASK));
helpMenu.add(helpItem);
menuBar.add(helpMenu);
JMenu aboutMenu = new JMenu("About");
JMenuItem aboutItem = new JMenuItem("About");
menuItem.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_A,
Event.CTRL_MASK));
aboutMenu.add(aboutItem);
menuBar.add(aboutMenu);
}
private void makeContent() {
Container contentPane = frame.getContentPane();
contentPane.setLayout(new BorderLayout());
JLabel label = new JLabel("Click a button to use its function");
label.setForeground(Color.white);
label.setFont(new Font("Lucida Console", Font.PLAIN, 14));
contentPane.add(label, BorderLayout.NORTH);
panel = new JPanel();
panel.setLayout(new BoxLayout(panel,BoxLayout.Y_AXIS));
panel.setLayout(new BoxLayout(panel,BoxLayout.Y_AXIS));
panel.setBackground(Color.DARK_GRAY);
JButton createButton = new JButton("Create Cipher");
createButton.addActionListener(new NewListener());
createButton.setBackground(Color.DARK_GRAY);
createButton.setFont(new Font("Lucida Console", Font.PLAIN, 14));
createButton.setForeground(Color.green);
panel.add(createButton);
JButton readButton = new JButton("Read Cipher");
readButton.addActionListener(new ReadListener());
readButton.setBackground(Color.DARK_GRAY);
readButton.setFont(new Font("Lucida Console", Font.PLAIN, 14));
readButton.setForeground(Color.green);
panel.add(readButton);
JButton aboutButton = new JButton("About Cipher Creator.......");
aboutButton.setBackground(Color.DARK_GRAY);
aboutButton.setFont(new Font("Lucida Console", Font.PLAIN, 14));
aboutButton.setForeground(Color.green);
panel.add(aboutButton);
JButton helpButton = new JButton("Help");
helpButton.setBackground(Color.DARK_GRAY);
helpButton.setFont(new Font("Lucida Console", Font.PLAIN, 14));
helpButton.setForeground(Color.green);
panel.add(helpButton);
frame.add(panel, BorderLayout.WEST);
JButton saveButton = new JButton("Save Cipher");
saveButton.addActionListener(new SaveListener());
saveButton.setBackground(Color.DARK_GRAY);
saveButton.setFont(new Font("Lucida Console", Font.PLAIN, 14));
saveButton.setForeground(Color.green);
panel.add(saveButton);
textArea = new JTextArea(0,0);
scrollArea = new JScrollPane(textArea);
scrollArea.setVerticalScrollBarPolicy(
ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED);
scrollArea.setHorizontalScrollBarPolicy(
ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED);
panel.add(scrollArea);
contentPane.add(textArea, BorderLayout.CENTER);
}
private class NewListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
textArea.setText("");
textArea.append("Type your message to be ciphered below, then click 'Save Cipher'. Remember, everything in the text area will be in your message, so delete this line.\n");
}
}
private class SaveListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
createCipher();
}
}
private class ReadListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
textArea.setText("");
JFileChooser fc = new JFileChooser();
fc.showOpenDialog(frame);
cipherFile = fc.getSelectedFile();
if (cipherFile == null) {
return;
}
readCipher();
}
}
private void readCipher() {
try
{
Scanner scan = new Scanner(cipherFile);
while (scan.hasNext())
{
String cipher = scan.next();
textArea.append(cipher);
textArea.append("\n");
}
scan.close();
}
catch(IOException e)
{
JOptionPane.showMessageDialog(frame,
"I/O error in file\n\n " +
cipherFile.getName() +
"\n\nThis program will close",
"I/O Error",
JOptionPane.ERROR_MESSAGE);
System.exit(1);
}
}
private void createCipher() {
try
{
cipher = textArea.getText();
PrintStream oFile = new PrintStream("Message.txt");
message = new File("Message.txt");
oFile.print(cipher);
oFile.close();
}
catch(IOException ioe)
{
System.out.println("\n*** I/O Error ***\n" + ioe);
}
try {
PrintStream oFile = new PrintStream("Cipher.txt");
rot = random.nextInt(5) + 1;
scan = new Scanner(message);
while (scan.hasNext()) {
cipherWord = scan.next();
l = cipherWord.length();
charScan = new Scanner(cipherWord);
for(int i = 0; i < cipherWord.length(); i++){
cipherChar = cipherWord.charAt(i);
if (cipherChar == 'a') {
cipherChar = 'b';
} else if (cipherChar == 'b') {
cipherChar = 'c';
} else if (cipherChar == 'c') {
cipherChar = 'd';
} else if (cipherChar == 'd') {
cipherChar = 'e';
} else if (cipherChar == 'e') {
cipherChar = 'f';
} else if (cipherChar == 'f') {
cipherChar = 'g';
} else if (cipherChar == 'g') {
cipherChar = 'h';
} else if (cipherChar == 'h') {
cipherChar = 'i';
} else if (cipherChar == 'i') {
cipherChar = 'j';
} else if (cipherChar == 'j') {
cipherChar = 'k';
} else if (cipherChar == 'k') {
cipherChar = 'l';
} else if (cipherChar == 'l') {
cipherChar = 'm';
} else if (cipherChar == 'm') {
cipherChar = 'n';
} else if (cipherChar == 'n') {
cipherChar = 'o';
} else if (cipherChar == 'o') {
cipherChar = 'p';
} else if (cipherChar == 'p') {
cipherChar = 'q';
} else if (cipherChar == 'q') {
cipherChar = 'r';
} else if (cipherChar == 'r') {
cipherChar = 's';
} else if (cipherChar == 's') {
cipherChar = 't';
} else if (cipherChar == 't') {
cipherChar = 'u';
} else if (cipherChar == 'u') {
cipherChar = 'v';
} else if (cipherChar == 'v') {
cipherChar = 'w';
} else if (cipherChar == 'w') {
cipherChar = 'x';
} else if (cipherChar == 'x') {
cipherChar = 'y';
} else if (cipherChar == 'y') {
cipherChar = 'z';
} else if (cipherChar == 'z') {
cipherChar = 'a';
}
oFile.print(cipherChar);
}
oFile.print(" ");
}
oFile.close();
scan.close();
charScan.close();
}
catch(Exception ioe) {
System.out.println("\n*** Print to Cipher.txt Error ***\n" + ioe);
}
viewCipher();
}
private void viewCipher() {
textArea.append("\nBelow is the cipher you created.\n Now you can copy/paste in and email it to the desired recipient.");
try
{
File Cipher = new File("Cipher.txt");
Scanner scan = new Scanner(Cipher);
textArea.append("\n");
while (scan.hasNextLine())
{
String cipher = scan.nextLine();
textArea.append(cipher);
textArea.append("\n");
}
}
catch(IOException e)
{
JOptionPane.showMessageDialog(frame,
"I/O error in file\n\n " +
cipherFile.getName() +
"\n\nThis program will close",
"I/O Error",
JOptionPane.ERROR_MESSAGE);
System.exit(1);
}
}
private class ExitListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
System.exit(0);
}
}
}
import java.awt.*；
导入java.awt.event.*；
导入java.util.*；
导入java.util.Random；
导入javax.swing.*；
导入java.io.*；
公共类代码生成器{
公共卫生；
公共JScrollPane滚动区；
公共随机；
公共文件密码；
公共国际；
公共文件信息；
公共字符-密码字符；
公共字符串finalCipher；
公共扫描仪；
公共扫描仪扫描；
公共字符串密码；
公共INTZ；
公共整型词；
公共文件加密文件；
公共int n；
公共字符串密码；
公共JPanel小组；
公共JButton保存按钮；
公共区域文本区域；
布尔创建=真；
私有JFrame；
公共静态void main（字符串[]args）{
CodeMaker gui=新的CodeMaker（）；
gui.start（）；
}
私有void start（）{
框架=新的JFrame（“战壕工程：密码创建者”）；
frame.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）；
frame.getContentPane（）.setBackground（颜色：深灰色）；
makeMenus（）；
makeContent（）；
frame.setVisible（true）；
frame.setExtendedState（frame.MAXIMIZED_两者）；
}
私有void makemenu（）{
梅努巴；
menuBar=newjmenubar（）；
frame.setJMenuBar（菜单栏）；
JMenu菜单；
菜单=新JMenu（“文件”）；
JMenuItem menuItem=新的JMenuItem（“新密码”）；
menuItem.addActionListener（newNewListener（））；
menuItem.setAccelerator(
KeyStroke.getKeyStroke（KeyEvent.VK_N，
事件。CTRL_掩码）；
menu.add（menuItem）；
JMenuItem menuitem=新的JMenuItem（“读取密码”）；
menuitem.setAccelerator(
KeyStroke.getKeyStroke（KeyEvent.VK_R，
事件。CTRL_掩码）；
menu.add（menuitem）；
menu.addSeparator（）；
menuItem=新项目（“退出”）；
menuItem.addActionListener（新的ExitListener（））；
menuItem.setAccelerator(
KeyStroke.getKeyStroke（KeyEvent.VK_Q，
事件。CTRL_掩码）；
menu.add（menuItem）；
菜单栏。添加（菜单）；
JMenu helpMenu=新JMenu（“帮助”）；
JMenuItem helpItem=新的JMenuItem（“帮助”）；
menuItem.setAccelerator(
KeyStroke.getKeyStroke（KeyEvent.VK_H，
事件。CTRL_掩码）；
帮助菜单。添加（帮助项）；
菜单栏。添加（帮助菜单）；
JMenu aboutMenu=新JMenu（“关于”）；
JMenuItem aboutItem=新的JMenuItem（“关于”）；
menuItem.setAccelerator
random = new Random();
Random random;
//later on somewhere
random = new Random();