Java How to implement a Shift Cipher Caesar Cipher

Question

I want to implement a Caesar Cipher shift to increase each letter in a string by 3     I am receiving this error    possible loss of precision required char  found int   Here is my code so far   import java util Scanner  import java io     public class CaesarCipher       public static void main  String    args             char   letters     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   message    onceuponatime  toCharArray            char   eMessage   new char message length           char shift   3             encrypting message         for int i   0  i  lt   message length    i                        eMessage i     message i    shift     char  letters length              System out println x                                                    What causes this error   How can I implement a caesar Cipher shift to increase each letter in a string by 3

User · Answer

Below code handles upper and lower cases as well and leaves other character as it is   import java util Scanner   public class CaesarCipher       public static void main String   args            Scanner in   new Scanner System in       int length   Integer parseInt in nextLine         String str   in nextLine        int k   Integer parseInt in nextLine          k   k   26       System out println encrypt str  length  k         in close               private static String encrypt String str  int length  int shift            StringBuilder strBuilder   new StringBuilder        char c      for  int i   0  i  lt  length  i                  c   str charAt i              if c is letter ONLY then shift them  else directly add it         if  Character isLetter c                     c    char   str charAt i    shift              System out println c               checking case or range check is important  just if  c  gt   z                c  gt   Z              will not work         if   Character isLowerCase str charAt i    amp  amp  c  gt   z                   Character isUpperCase str charAt i    amp  amp  c  gt   Z                 c    char   str charAt i  -  26 - shift                      strBuilder append c             return strBuilder toString

User · Answer

Java Shift Caesar Cipher by shift spaces   Restrictions    Only works with a positive number in the shift parameter   Only works with shift less than 26  Does a    which will bog the computer down for bodies of text longer than a few thousand characters  Does a cast number to character  so it will fail with anything but ascii letters  Only tolerates letters a through z   Cannot handle spaces  numbers  symbols or unicode  Code violates the DRY  don t repeat yourself  principle by repeating the calculation more than it has to    Pseudocode    Loop through each character in the string  Add shift to the character and if it falls off the end of the alphabet then subtract shift from the number of letters in the alphabet  26  If the shift does not make the character fall off the end of the alphabet  then add the shift to the character  Append the character onto a new string  Return the string    Function   String cipher String msg  int shift       String s           int len   msg length        for int x   0  x  lt  len  x             char c    char  msg charAt x    shift           if  c  gt   z               s     char  msg charAt x  -  26-shift            else             s     char  msg charAt x    shift             return s      How to invoke it   System out println cipher  abc   3       prints def System out println cipher  xyz   3       prints abc

User · Answer

The warning is due to you attempting to add an integer  int shift   3  to a character value  You can change the data type to char if you want to avoid that   A char is 16 bits  an int is 32   char shift   3         eMessage i     message i    shift     char letters length    As an aside  you can simplify the following   char   message     o    n    c    e    u    p    o    n    a    t    i    m    e       To   char   message    onceuponatime  toCharArray

User · Answer

Two ways to implement a Caesar Cipher   Option 1   Change chars to ASCII numbers  then you can increase the value  then revert it back to the new character   Option 2  Use a Map map each letter to a digit like this     A - 0 B - 1 C - 2 etc      With a map you don t have to re-calculate the shift every time   Then you can change to and from plaintext to encrypted by following map

User · Answer

Hello   I have created a java client server application in swing for caesar cipher   I have created a new formula that can decrypt the text properly    sorry only for lower case     import java awt    import java awt event    import javax swing    import java io    import java net    import java util     public class ceasarserver extends JFrame implements ActionListener       static String cs    abcdefghijklmnopqrstuvwxyz       static JLabel l1  l2  l3  l5  l6      JTextField t1      JButton close  b1      static String en      int num   0      JProgressBar progress       ceasarserver             super  SERVER            JPanel p   new JPanel new GridLayout 10  1            l1   new JLabel              l2   new JLabel              l3   new JLabel              l5   new JLabel              l6   new JLabel  Enter the Key               t1   new JTextField 30           progress   new JProgressBar 0  20           progress setValue 0           progress setStringPainted true           close   new JButton  Close            close setMnemonic  C            close setPreferredSize new Dimension 300  25            close addActionListener this           b1   new JButton  Decrypt            b1 setMnemonic  D            b1 addActionListener this           p add l1           p add l2           p add l3           p add l6           p add t1           p add b1           p add progress           p add l5           p add close           add p           setVisible true           pack               public void actionPerformed ActionEvent e            if  e getSource      close              System exit 0           else if  e getSource      b1                int key   Integer parseInt t1 getText                 String d                   int i   0  j  k              while  i  lt  en length                      j   cs indexOf en charAt i                    k    j    26 - key     26                  d   d   cs charAt k                   i                              while  num  lt  21                    progress setValue num                   try                       Thread sleep 100                     catch  InterruptedException ex                                      progress setValue num                   Rectangle progressRect   progress getBounds                    progressRect x   0                  progressRect y   0                  progress paintImmediately progressRect                   num                              l5 setText  Decrypted text      d                        public static void main String args    throws IOException           new ceasarserver            String strm   new String            ServerSocket ss   new ServerSocket 4321           l1 setText  Secure data transfer Server Started                Socket s   ss accept            l2 setText  Client Connected              while  true                Scanner br1   new Scanner s getInputStream                 en   br1 nextLine                l3 setText  Client     en                     The client class   import java awt    import java awt event    import javax swing    import java io    import java net    import java util     public class ceasarclient extends JFrame       String cs    abcdefghijklmnopqrstuvwxyz       static JLabel l1  l2  l3  l4  l5      JButton b1  b2  b3      JTextField t1  t2      JProgressBar progress      int num   0      String en            ceasarclient final Socket s            super  CLIENT            JPanel p   new JPanel new GridLayout 10  1            setSize 500  500           t1   new JTextField 30           b1   new JButton  Send            b1 setMnemonic  S            b2   new JButton  Close            b2 setMnemonic  C            l1   new JLabel  Welcome to Secure Data transfer             l2   new JLabel  Enter the word here               l3   new JLabel              l4   new JLabel  Enter the Key             b3   new JButton  Encrypt            b3 setMnemonic  E            t2   new JTextField 30           progress   new JProgressBar 0  20           progress setValue 0           progress setStringPainted true           p add l1           p add l2           p add t1           p add l4           p add t2           p add b3           p add progress           p add b1           p add l3           p add b2           add p           setVisible true           b1 addActionListener new ActionListener                 public void actionPerformed ActionEvent e                    try                       PrintWriter pw   new PrintWriter s getOutputStream    true                       pw println en                     catch  Exception ex                                                        l3 setText  Encrypted Text Sent                                       b3 addActionListener new ActionListener                 public void actionPerformed ActionEvent e                    String strw   t1 getText                    int key   Integer parseInt t2 getText                     int i   0  j  k                  while  i  lt  strw length                          j   cs indexOf strw charAt i                        k    j   key    26                      en   en   cs charAt k                       i                                      while  num  lt  21                        progress setValue num                       try                           Thread sleep 100                         catch  InterruptedException exe                                              progress setValue num                       Rectangle progressRect   progress getBounds                        progressRect x   0                      progressRect y   0                      progress paintImmediately progressRect                       num                                                        b2 addActionListener new ActionListener                 public void actionPerformed ActionEvent e                    System exit 0                                     pack               public static void main String args    throws IOException           final Socket s   new Socket InetAddress getLocalHost    4321           new ceasarclient s

[java] Java, How to implement a Shift Cipher (Caesar Cipher)

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