Understanding TimeUnit

Question

I took a look into TimeUnit and toMillis() method.

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

toMillis() method do nothing other than throw an AbstractMethodError exception.

So, How does toMillis() method convert seconds, minutes, etc to milliseconds?

TimeUnit is basically the abstract prototype. You need to look into concrete `TimeUnits`, such as `TimeUnit.SECONDS` — rethab, Oct 05 '16 at 05:19

score 7 · Answer 1 · answered Oct 05 '16 at 03:50

7

Each value within TimeUnit overrides it, basically. You never end up calling that implementation, because you never have a reference to an object of type TimeUnit - it's always a subclass representing one of the values.

answered Oct 05 '16 at 03:50

Jon Skeet

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score 3 · Accepted Answer · answered Oct 05 '16 at 04:02

Open the TimeUnit and look the constants inside...

/**
 * 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)); }
},

as you will see, every constant in the enumerator TimeUnit NANOSECONDS, MICROSECONDS etc implements anonymously methods that give you indirect access to toMillis() therefore this method

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

is never accessed by your code directly...

I saw the override methods in JDK but when I used decompiler to decompile 'TimeUnit' from JRE. The override methods are not there. Why does it happens? — Tran Thien Chien, Oct 05 '16 at 04:49

score 2 · Answer 3 · answered Oct 05 '16 at 03:53

2

It's method override.

You can see the overrided implementations in NANOSECONDS, MICROSECONDS and etc.

answered Oct 05 '16 at 03:53

Henry

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Understanding TimeUnit

3 Answers3