去除字符串的指定字符

假如有字符串“6sabcsssfsfs33” ，用最有快速的方法去掉字符“ab3”，不能用java内置字符串方法（indeOf,substring,replaceAll等）？

class Remove{ 
　public static void main(String args[]) { 
　　String str="6sabcsssfsfs33； 
    boolean removeChars[256] = {true};
    removeChars['a'] = false;
    removeChars['b'] = false;
    removeChars['3'] = false;
　　StringBuffer sb = new StringBuffer();
    for (char ch: str) {
        if (!removeChars[ch]) sb.append(ch);
    }
    String result = sb.toString();
　} 
} 

或者用正则

String regx="[^a|b|3]";   
String temp="6sabcsssfsfs33";   
Pattern p=Pattern.compile(regx);   
Matcher m=p.matcher(temp);   
if(m.find())   
     System.out.print(m.group());