java - 什么 Java 库对象封装了数字和 `TimeUnit`？

Question

我想传递一个时间数字和它所在的 TimeUnit。

long number = some number;
TimeUnit timeUnit = some arbitrary time unit

什么可以在 Java 库中的一个 Object 中同时保存时间和 timeUnit？

Answer 1

没有封装数字和任意TimeUnit 的Java 库对象。然而，Java 8 中有一个可以将自身转换为所需的任何时间单位:

java.time.Duration

Duration 存储提供的数量，然后提供与所有其他时间单位的比较和转换。例如:

// Create duration from nano time
Duration systemTime = Duration.ofNanos(System.nanoTime());

// Create duration from millis time
Duration systemTime = Duration.ofMillis(System.currentTimeMillis());

当然，如果进行加法和减法或其他数学运算，精度仅与当前运算的精度和提供的Duration 一样好。

/**
* Example that tells if something has reached the required age
* TRUE IF THE current system time is older or equal to the required system time
*/
    // TRUE IF THE FILE HAS NOT WAITED ENOUGH TIME AFTER LAST CREATE/MODIFY
    private boolean isMature() {
        // it is not known whether required age is nanos or millis
        Duration requiredAge = systemTimeWhenMature();
        // so create a duration in whatever time unit you have
        // more precise = possibly better here
        Duration actualAge = Duration.ofNanos(System.nanoTime());
       // if ON or OLDER THAN REQUIRED AGE
       // actualAge - requiredAge  = balance
       // 20 - 21 = -1 (NOT MATURE)
       // 21 - 21 =  0 (OK)
       // 22 - 21 =  1 (OK)
       Duration balance = actualAge.minus(requiredAge);
       if (balance.isNegative()) {
           logger.info("Something not yet expired. Expires in {} millis.", balance.negated());
           return false;
       } else {
           return true;
       }
    }

并且 Duration 中还有更多方法可用于转换和处理各种单位的存储量。

了解精度将如何影响计算非常重要。这表明通用精确合约示例:

    // PICK A NUMBER THAT IS NOT THE SAME WHEN CONVERTED TO A LESSER PRECISION
    long timeNanos = 1234567891011121314L;
    long timeMillis = TimeUnit.MILLISECONDS.convert(timeNanos, TimeUnit.NANOSECONDS);

    // create from milliseconds
    Duration millisAccurate = Duration.ofMillis(timeMillis);
    Duration nanosAccurate = Duration.ofNanos(timeNanos);

    // false because of precision difference
    assertFalse(timeMillis == timeNanos);
    assertFalse(millisAccurate.equals(nanosAccurate));

    // true because same logical precision conversion takes place
    assertTrue(timeMillis - timeNanos <= 0);
    assertTrue(millisAccurate.minus(nanosAccurate).isNegative());

    // timeNanos has greater precision and therefore is > timeMillie
    assertTrue(timeNanos - timeMillis > 0);
    assertTrue(nanosAccurate.minus(millisAccurate).negated().isNegative());

简而言之..我不敢相信我花了这么长时间才找到 Duration! :)