java - Trying to decipher a text file with an algorithm -

i have deciphering method should open test file encrypted text, read , decipher each line of text read in input file. text file called mystery.txt. can method work when inputting single characters can't work open .txt file , decipher line line. have tried calling readfile() before algorithm null pointer exception in (i = 0; < text.length(); i++) . have never done similar before , don't know how go doing it.

the algorithm should read each line , decipher using crypt1 & crypt2 variables.

using readfile() , writefile() methods, need cipherdecipherstring() method able write method opens file, reads each line contains 1 @ time, deciphers each line read in , writes resulting text screen , output file.

dechiphering method:

public static string cipherdecipherstring(string text)  {  // these global. put here space saving  private static final string crypt1 = "cipherabdfgjk";  private static final string crypt2 = "lmnoqstuvwxyz";      // declare variables     int i, j;     boolean found = false;     string temp="" ; // empty string hold converted text     readfile();     (i = 0; < text.length(); i++) // @ every chracter in text     {         found = false;         if ((j = crypt1.indexof(text.charat(i))) > -1) // char in crypt1?         {                        found = true; // yes!             temp = temp + crypt2.charat(j); // add cipher character temp         }         else if ((j = crypt2.indexof(text.charat(i))) > -1) // , on         {             found = true;             temp = temp + crypt1.charat(j);         }         if (! found) // deal cases char not in crypt2 or 2         {             temp = temp + text.charat(i); // copy across character         }     }     return temp; } 

my readfile method:

public static void readfile() {     filereader filereader = null;     bufferedreader bufferedreader = null;     string inputfilename;     string nextline;     clrscr();     system.out.println("please enter name of file read (e.g. afile.txt: ");     inputfilename = genio.getstring();     try     {         filereader = new filereader(inputfilename);         bufferedreader = new bufferedreader(filereader);          nextline = bufferedreader.readline();         while (nextline != null)         {             system.out.println(nextline);             nextline = bufferedreader.readline();         }     }     catch (ioexception e)     {         system.out.println("sorry, there has been problem opening or reading file");     }         {         if (bufferedreader != null)         {             try             {                 bufferedreader.close();                 }             catch (ioexception e)             {                 system.out.println("an error occurred when attempting close file");             }         }       } } 

my writefile() method:

public void writefile() {     string mystring;     clrscr();     system.out.println("begin typing contents wish write file: ");     mystring = genio.getstring();     system.out.println("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");     fileoutputstream outputstream = null;     printwriter printwriter = null;     try     {         outputstream = new fileoutputstream("writing.txt");         printwriter = new printwriter(outputstream);          printwriter.write(mystring);         printwriter.println("\n");         while (!mystring.equals(""))         {             mystring = genio.getstring();             printwriter.print(mystring + "\n");         }          system.out.println("file: 'writing.txt' has been saved contents above.\n\nyou can open file using other options in menu screen.");         presskey();     }     catch (ioexception e)     {         system.out.println("sorry, there has been problem opening or writing file");     }         {         if (printwriter != null)         {             // close file             printwriter.close();             }     } } 

now thought able call readfile() method go decipher code , let work it's way through file cannot work @ all.

genio class deals user input. didn't want go overkill code can post add if it's needed. thank you!

lets call cipherdecipherstring decode, put in method called decode takes 2 file paths. 1 source file path, other destination. here's how code like:

private static final string crypt1 = "cipherabdfgjk"; private static final string crypt2 = "lmnoqstuvwxyz";  private string decode (string line) {   stringbuilder result = new stringbuilder (line.length ());    (int = 0; < line.length (); ++i)   {     char ch = line.charat (i);      int index1 = crypt1.indexof (ch);     int index2 = crypt2.indexof (ch);      if (index1 != -1)     {       result.append (crypt2.charat (index1));     }     else if (index2 != -1)     {       result.append (crypt1.charat (index2));     }     else     {       result.append (ch);     }   }    return result.tostring (); }  /* takes file source, reads line line, decodes each line, writes  * decoded lines file destination.  */ public void decode (string filesource, string filedestination) throws ioexception {   files.write (paths.get (filedestination),                 files.lines (paths.get (filesource)).                map (this::decode).                collect (collectors.tolist ())); } 

this requires java 8 though. if have issues in cipherdecipherstring method, let me know.

these required imports:

import java.io.ioexception; import java.nio.file.files; import java.nio.file.paths; import java.util.stream.collectors;