为什么 Java 时间戳解析在毫秒部分以 0 为前缀？

Question

final String OLD_FORMAT = "mm:ss.SS";        
final String TARGET_FORMAT = "HH:mm:ss,SSS";           

String timeInputStr="00:17.20";  // input is always in mm.ss.SS m--> minutes, ss-> seconds , and SSS is decimal fraction of seconds always , not actual milliseconds 
String timeOutputStr="";
Date d=new Date();
DateFormat  formatter= new SimpleDateFormat(OLD_FORMAT); 
DateFormat nformatter= new SimpleDateFormat(TARGET_FORMAT);          
try{   
        d = formatter.parse(timeInputStr);
}
catch (ParseException e){
         System.out.println("Can't Parse date "+d + " from: " +lrcTime );
}

timeInputStr=nformatter.format(d);
System.out.println( "For Input String: " + lrcTime +  " -> Parsed date "+ formatter.format(d) +  "-> will print as to  " + timeInputStr);
return timeOutputStr;   

它给了我以下输出：

final String OLD_FORMAT = "mm:ss.SS";        
final String TARGET_FORMAT = "HH:mm:ss,SSS";           

String timeInputStr="00:17.20";  // input is always in mm.ss.SS m--> minutes, ss-> seconds , and SSS is decimal fraction of seconds always , not actual milliseconds 
String timeOutputStr="";
Date d=new Date();
DateFormat  formatter= new SimpleDateFormat(OLD_FORMAT); 
DateFormat nformatter= new SimpleDateFormat(TARGET_FORMAT);          
try{   
        d = formatter.parse(timeInputStr);
}
catch (ParseException e){
         System.out.println("Can't Parse date "+d + " from: " +lrcTime );
}

timeInputStr=nformatter.format(d);
System.out.println( "For Input String: " + lrcTime +  " -> Parsed date "+ formatter.format(d) +  "-> will print as to  " + timeInputStr);
return timeOutputStr;   

但我想解析这样的字符串 00:00:17,200

我错过了什么？

Answer 1

在较新的日期时间类中改进了歧义：

旧的SimpleDateFormat

• S = 毫秒

  SS 为 20 表示 20 ms，因此 SSS 将为 020 ms。

较新的DateTimeFormatter

• S = 秒的分数。

  会给 SSS = 200 毫秒

新解释背后的基本原理是，微秒和纳秒 2 毫秒,2并不真正适合诸如,SSSSSS- 正如您所说的那样。