public static String replaceStr(String str){		StringBuffer buffer = new StringBuffer(str);		buffer.replace(1, buffer.length(), "**");				return buffer.toString();	}		public static String replaceStr2(String str){		StringBuffer buffer = new StringBuffer(str);		buffer.replace(3, 7, "****");				return buffer.toString();	}

调用：

replaceStr("张振武");replaceStr2("18221801233");