瞭解TimeUnit

Question

我看了一下TimeUnit和toMillis()的方法。

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

toMillis()方法做無非拋出一個異常AbstractMethodError等。

那麼，toMillis()方法如何將秒，分鐘等轉換爲毫秒？

Answer 1

打開TIMEUNIT並往裏常數...

/** 
* 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)); } 
}, 

，你會看到，在枚舉TIMEUNIT每一個常數 納秒，MICROSECONDS等實現匿名，讓你間接訪問toMillis()因此這種方法方法

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

永遠不會被您的代碼直接訪問...

Answer 2

基本上，TimeUnit中的每個值都會覆蓋它。您永遠不會調用該實現，因爲您永遠不會引用TimeUnit類型的對象 - 它始終是表示其中一個值的子類。

Answer 3

這是方法重寫。

你可以看到在納秒，微秒overrided實現等