TimeUnit使用和解析
一、TimeUnit.sleep
1.1 使用
睡眠一段时间，通常使用的是Thread.sleep方法，代码如下：
public static void testSleep() throws InterruptedException {
Thread.sleep(1000 * 60 * 5);
}上述代码表示睡眠5分钟，可读性不好。如果使用TimeUnit，代码如下：
public static void testTimeUnitSleep() throws InterruptedException {
TimeUnit.MINUTES.sleep(5);
}TimeUnit.sleep的可读性明显高于Thread.sleep。
1.2 代码解析
public void sleep(long timeout) throws InterruptedException {
if (timeout > 0) {
long ms = toMillis(timeout); // 转换成毫秒
int ns = excessNanos(timeout, ms); // 取纳秒
Thread.sleep(ms, ns); // 调用Thread.sleep
}
}本质就是对Thread.sleep(long millis)的一个封装，提供了时间转换操作。
二、TimeUnit.timedWait
2.1 使用
public static void testTimeUnitWait() throws InterruptedException {
Object lock = new Object();
synchronized (lock) {
TimeUnit.MINUTES.timedWait(lock, 5);
}
}2.2 代码解析
public void timedWait(Object obj, long timeout) throws InterruptedException {
if (timeout > 0) {
long ms = toMillis(timeout);
int ns = excessNanos(timeout, ms);
obj.wait(ms, ns);
}
}本质就是对Object.wait(long timeout)的一个封装，，提供了时间转换操作。
三、TimeUnit.timedJoin
3.1 使用
public static void testTimeUnitJoin() throws InterruptedException {
Thread thread = new Thread(() -> {
System.out.println("run");
try {
TimeUnit.MINUTES.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Over run.");
});
thread.start();
TimeUnit.MINUTES.timedJoin(thread, 5);
System.out.println("Over Main.");
}3.2 代码解析
public void timedJoin(Thread thread, long timeout) throws InterruptedException {
if (timeout > 0) {
long ms = toMillis(timeout);
int ns = excessNanos(timeout, ms);
thread.join(ms, ns);
}
}本质就是对Thread.join(long millis)的一个封装，，提供了时间转换操作。
四、TimeUnit.toXXX
4.1 简单使用
System.out.println(TimeUnit.SECONDS.toMinutes(10)); // 0
System.out.println(TimeUnit.SECONDS.toMinutes(65)); // 1
System.out.println(TimeUnit.MILLISECONDS.toMicros(1)); // 1毫秒=1000微秒
System.out.println(TimeUnit.MICROSECONDS.toNanos(1)); // 1微秒=1000纳秒4.2 解析
TimeUnit提供了以下方法来转换时间：
toNanos(long)
toMicros(long)
toMillis(long)
toSeconds(long)
toMinutes(long)
toHours(long)
toDays(long)注：从小单位转换成大单位用的整除，直接取整，比如65秒为1分钟多一点，那么转换成分钟只取整数。以下为SECONDS.toMinutes实现，C4=60000000000，C3=1000000000。
public long toMinutes(long d) { return d/(C4/C3); }五、TimeUnit部分代码
TimeUnit本质就是一个枚举，是学习枚举的好例子。
public enum TimeUnit {
/**
* 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)); }
},
/**
* Time unit representing one thousandth of a second
*/
MILLISECONDS {
public long toNanos(long d) { return x(d, C2/C0, MAX/(C2/C0)); }
public long toMicros(long d) { return x(d, C2/C1, MAX/(C2/C1)); }
public long toMillis(long d) { return d; }
public long toSeconds(long d) { return d/(C3/C2); }
public long toMinutes(long d) { return d/(C4/C2); }
public long toHours(long d) { return d/(C5/C2); }
public long toDays(long d) { return d/(C6/C2); }
public long convert(long d, TimeUnit u) { return u.toMillis(d); }
int excessNanos(long d, long m) { return 0; }
},
/**
* Time unit representing one second
*/
SECONDS {
public long toNanos(long d) { return x(d, C3/C0, MAX/(C3/C0)); }
public long toMicros(long d) { return x(d, C3/C1, MAX/(C3/C1)); }
public long toMillis(long d) { return x(d, C3/C2, MAX/(C3/C2)); }
public long toSeconds(long d) { return d; }
public long toMinutes(long d) { return d/(C4/C3); }
public long toHours(long d) { return d/(C5/C3); }
public long toDays(long d) { return d/(C6/C3); }
public long convert(long d, TimeUnit u) { return u.toSeconds(d); }
int excessNanos(long d, long m) { return 0; }
},
/**
* Time unit representing sixty seconds
*/
MINUTES {
public long toNanos(long d) { return x(d, C4/C0, MAX/(C4/C0)); }
public long toMicros(long d) { return x(d, C4/C1, MAX/(C4/C1)); }
public long toMillis(long d) { return x(d, C4/C2, MAX/(C4/C2)); }
public long toSeconds(long d) { return x(d, C4/C3, MAX/(C4/C3)); }
public long toMinutes(long d) { return d; }
public long toHours(long d) { return d/(C5/C4); }
public long toDays(long d) { return d/(C6/C4); }
public long convert(long d, TimeUnit u) { return u.toMinutes(d); }
int excessNanos(long d, long m) { return 0; }
},
/**
* Time unit representing sixty minutes
*/
HOURS {
public long toNanos(long d) { return x(d, C5/C0, MAX/(C5/C0)); }
public long toMicros(long d) { return x(d, C5/C1, MAX/(C5/C1)); }
public long toMillis(long d) { return x(d, C5/C2, MAX/(C5/C2)); }
public long toSeconds(long d) { return x(d, C5/C3, MAX/(C5/C3)); }
public long toMinutes(long d) { return x(d, C5/C4, MAX/(C5/C4)); }
public long toHours(long d) { return d; }
public long toDays(long d) { return d/(C6/C5); }
public long convert(long d, TimeUnit u) { return u.toHours(d); }
int excessNanos(long d, long m) { return 0; }
},
/**
* Time unit representing twenty four hours
*/
DAYS {
public long toNanos(long d) { return x(d, C6/C0, MAX/(C6/C0)); }
public long toMicros(long d) { return x(d, C6/C1, MAX/(C6/C1)); }
public long toMillis(long d) { return x(d, C6/C2, MAX/(C6/C2)); }
public long toSeconds(long d) { return x(d, C6/C3, MAX/(C6/C3)); }
public long toMinutes(long d) { return x(d, C6/C4, MAX/(C6/C4)); }
public long toHours(long d) { return x(d, C6/C5, MAX/(C6/C5)); }
public long toDays(long d) { return d; }
public long convert(long d, TimeUnit u) { return u.toDays(d); }
int excessNanos(long d, long m) { return 0; }
};
// Handy constants for conversion methods
static final long C0 = 1L;
static final long C1 = C0 * 1000L;
static final long C2 = C1 * 1000L;
static final long C3 = C2 * 1000L;
static final long C4 = C3 * 60L;
static final long C5 = C4 * 60L;
static final long C6 = C5 * 24L;
static final long MAX = Long.MAX_VALUE;
/**
* Scale d by m, checking for overflow.
* This has a short name to make above code more readable.
*/
static long x(long d, long m, long over) {
if (d > over) return Long.MAX_VALUE;
if (d < -over) return Long.MIN_VALUE;
return d * m;
}