String are immutable in Java. You can‘t change them.

You need to create a new string with the character replaced.

String myName = "domanokz";String newName = myName.substring(0,4)+‘x‘+myName.substring(5);

or you can use a StringBuilder:

StringBuilder myName = new StringBuilder("domanokz");myName.setCharAt(4, ‘x‘);System.out.println(myName);

http://stackoverflow.com/questions/6952363/java-replace-a-character-at-a-specific-index-in-a-string

Java - replace a character at a specific index in a string?