java - 了解时间单位

Question

我看了看TimeUnit和toMillis()方法。

 public long toMillis(long paramLong)
 {
    throw new AbstractMethodError();
 }

toMillis()AbstractMethodError方法除了抛出异常什么都不做。

那么，toMillis()方法如何将秒、分钟等转换为毫秒？

Answer 1

TimeUnit基本上，其中的每个值都会覆盖它。您永远不会最终调用该实现，因为您永远不会引用类型对象TimeUnit- 它始终是表示其中一个值的子类。

Answer 2

打开 TimeUnit 并查看里面的常量...

/**
 * Time unit representing one thousandth of a microsecond
 */
NANOSECONDS {
    public long toNanos(long d)   { return d; }
    public long toMicros(long d)  { return d/(C1/C0); }
    public long toMillis(long d)  { return d/(C2/C0); }
    public long toSeconds(long d) { return d/(C3/C0); }
    public long toMinutes(long d) { return d/(C4/C0); }
    public long toHours(long d)   { return d/(C5/C0); }
    public long toDays(long d)    { return d/(C6/C0); }
    public long convert(long d, TimeUnit u) { return u.toNanos(d); }
    int excessNanos(long d, long m) { return (int)(d - (m*C2)); }
},

/**
 * Time unit representing one thousandth of a millisecond
 */
MICROSECONDS {
    public long toNanos(long d)   { return x(d, C1/C0, MAX/(C1/C0)); }
    public long toMicros(long d)  { return d; }
    public long toMillis(long d)  { return d/(C2/C1); }
    public long toSeconds(long d) { return d/(C3/C1); }
    public long toMinutes(long d) { return d/(C4/C1); }
    public long toHours(long d)   { return d/(C5/C1); }
    public long toDays(long d)    { return d/(C6/C1); }
    public long convert(long d, TimeUnit u) { return u.toMicros(d); }
    int excessNanos(long d, long m) { return (int)((d*C1) - (m*C2)); }
},

正如您将看到的，枚举器 TimeUnit NANOSECONDS、MICROSECONDS等中的每个常量都实现了匿名方法，从而使您可以间接访问toMillis()此方法

 public long toMillis(long duration) {
        throw new AbstractMethodError();
    }

您的代码永远不会直接访问...

Answer 3

它是方法覆盖。

您可以在 NANOSECONDS、MICROSECONDS 等中看到被覆盖的实现。