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?
原文：http://www.cnblogs.com/savagemorgan/p/4059044.html