String s = "abcdabc";
String tt = "bc";
String ttt = "e";
int index = 0;
while (s.indexOf("bc", index) != -1) {
index = s.indexOf("bc", index);
s = s.substring(0, index) + ttt + s.substring(index + tt.length());
}
System.out.println(s);
原文：http://www.cnblogs.com/apanda009/p/7952874.html