java - replace random number of characters at random position with wildcard -

i trying create program replace random number of characters @ random position "*". star letter used in main program , replaced "." wildcard matches possible result.

so far manage create code see bellow. replaces 1 character of specific word. here on appreciated.

example:

input word: mouse

random generator how characters replace: 3

random generator @ places replace: 1, 3, 5

result: *o*s*

public class random_2 {  public static void main(string[] args) {     string test;     int dolzina = 0;     string outputfile = "random_2.txt";     arraylist<string> list = new arraylist();      try {          file file = new file("random1.txt");         filereader filereader = new filereader(file);         bufferedreader bufferedreader = new bufferedreader(filereader);         string vrstica;         while ((vrstica = bufferedreader.readline()) != null) {              list.add(vrstica);             // dolzina=list.size();             // system.out.println(dolzina);          }          filewriter filewriter = new filewriter(outputfile);         printwriter out = new printwriter(filewriter);         (int idx = 0; idx <= list.size(); ++idx) {             test=list.get(idx);             dolzina=test.length();              random rgenerator = new random();              (int = 0; i<= dolzina; ++i) {                 int randomint = rgenerator.nextint(dolzina);                 stringbuilder beseda = new stringbuilder(test);                 beseda.setcharat(randomint, '*');                 system.out.println(beseda);                 dolzina=0;         }}          system.out.println("done.");      } catch (ioexception e) {         e.printstacktrace();      } } } 

modified code , working:

try {          file file = new file("random1.txt");         filereader filereader = new filereader(file);         bufferedreader bufferedreader = new bufferedreader(filereader);         string vrstica = bufferedreader.readline();         while (vrstica != null) {              list.add(vrstica);             vrstica = bufferedreader.readline();             // dolzina=list.size();             // system.out.println(dolzina);          }          filewriter filewriter = new filewriter(outputfile);         printwriter out = new printwriter(filewriter);          (int idx = 0; idx < list.size(); ++idx) {             test = list.get(idx);             dolzina = test.length();              random rgenerator = new random();             stringbuilder beseda = new stringbuilder(test);              (int = 0; < dolzina; ++i) {                 int randomint = rgenerator.nextint(dolzina);                  beseda.setcharat(randomint, '*');                 system.out.println(beseda);              }             out.print(beseda);             out.close();         }