Someone

StringBuffer ret = new StringBuffer();
char c; 
for(int i=0; i < in.length(); i++) {
	switch((c=in.charAt(i))) {
		case '<': ret.append("<") ; break; 
		case '>': ret.append(">") ; break; 
		case '&': ret.append("&"); break; 
		default:  ret.append(c); break; 
	}
}
return ret.toString();