Here is an example that replaces the vowels of string with the z and reverse the string.

class StringExamples 
    {
        public static void main(String[] args) 
        {
            String st="John Smith";
            String replaceString=st.replaceAll("[aeiou](?!\\b)", "z");
            System.out.println(replaceString);
            char ch[]=st.toCharArray();
            String revstring="";
            for(int i=ch.length-1;i>=0;i--){
                revstring+=Character.toString(ch[i]);
            }
            System.out.println(revstring);

        }
    }