TimeUnit类用于控制时间和sleep的方法栈
10^6^纳秒=10^3^微秒=1毫秒
1. 枚举使用
这种在枚举外调用枚举中声明的方法的设计思路很有意思，也算是动态调用？
- 定义抽象方法doWork()，可在具体枚举值中实现不同枚举值进行不同的处理;
- 定义调用参数方法invokeWorker()，调用不同枚举值的抽象方法的实现；
demo如下：
public class EnumTest {
enum EnumDemo{
DEMOX("demoX"){
@Override
void enumFunc(){
System.out.println(getName());
}
},
DEMOY("demoY"){
@Override
void enumFunc(){
System.out.println(getName());
}
};
abstract void enumFunc();
public void invokeEnumFunc(){
enumFunc();
}
private String name;
EnumDemo(String name){this.name=name;}
public String getName() {
return name;
}
}
public static void main(String[] args) {
EnumDemo.DEMOX.invokeEnumFunc();
EnumDemo.DEMOY.invokeEnumFunc();
}
}
output:
demoX
demoY
2.源码讲解
- 所有时间单位都是一个包含转换方法的枚举，进率保存常量中；
- 大时间单位转小时间单位的时候会判断一下是否溢出， 需要判定上下界，因为基数为负则可能下界溢出。
- TimeUnit.时间单位SECOND/NANOSECONDS.sleep(10n)的调用栈；
public enum TimeUnit {
// Handy constants for conversion methods
static final long C0 = 1L;//纳秒
static final long C1 = C0 * 1000L;//纳秒-》微秒
static final long C2 = C1 * 1000L;//纳秒-》毫秒
static final long C3 = C2 * 1000L;//纳秒-》秒
static final long C4 = C3 * 60L;//纳秒-》分钟
static final long C5 = C4 * 60L;//纳秒-》小时
static final long C6 = C5 * 24L;//纳秒-》天
static final long MAX = Long.MAX_VALUE;
/**
* 纳秒
*/
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; }
};
/**
* Scale d by m, checking for overflow:
*校验转换成更小的时间单位是，返回值是否会溢出：溢出则返回上下界
* @param d 被转换值，可为负，所以需要判定下界
* @param m 转换成更小的单位时需要想乘的因子
* @param over 保证d*m不溢出的上下限
*/
static long x(long d, long m, long over) {
if (d > over) return Long.MAX_VALUE;
//注意：因为负数乘以因子后会接近与Long.MIN_VALUE
if (d < -over) return Long.MIN_VALUE;
return d * m;
}
//TimeUnit.XXX.sleep调用此方法，如果时间单位比毫秒小，四舍五入(在sleep方法中)
public void sleep(long timeout) throws InterruptedException {
if (timeout > 0) {
long ms = toMillis(timeout);
//纳秒：int excessNanos(long d, long m) { return (int)(d - (m*C2)); }
//微秒：int excessNanos(long d, long m) { return (int)((d*C1) - (m*C2)); }
//excessNanos用于求timeout转换成毫秒后的纳秒余数，用于休眠时四舍五入
int ns = excessNanos(timeout, ms);
Thread.sleep(ms, ns);
}
}
//Thread中的类：睡眠指定时间，nano四舍五入加在Millis上。如果超范围会抛异常
public static void sleep(long millis, int nanos)
throws InterruptedException {
if (millis < 0) {
throw new IllegalArgumentException("timeout value is negative");
}
if (nanos < 0 || nanos > 999999) {
throw new IllegalArgumentException(
"nanosecond timeout value out of range");
}
if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
millis++;
}
sleep(millis);//native方法
}
/**
* 用于计算wait、sleep和join时，多余的纳秒的工具类。
* Utility to compute the excess-nanosecond argument to wait,
* sleep, join.
* @param d the duration
* @param m the number of milliseconds
* @return the number of nanoseconds
*/
abstract int excessNanos(long d, long m);
/**
* Performs a timed {@link Object#wait(long, int) Object.wait}
* using this time unit.
* This is a convenience method that converts timeout arguments
* into the form required by the {@code Object.wait} method.
*
* <p>For example, you could implement a blocking {@code poll}
* method (see {@link BlockingQueue#poll BlockingQueue.poll})
* using:
*
* <pre> {@code
* public synchronized Object poll(long timeout, TimeUnit unit)
* throws InterruptedException {
* while (empty) {
* unit.timedWait(this, timeout);
* ...
* }
* }}</pre>
*
* @param obj the object to wait on
* @param timeout the maximum time to wait. If less than
* or equal to zero, do not wait at all.
* @throws InterruptedException if interrupted while waiting
*/
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);
}
}
/**
* Performs a timed {@link Thread#join(long, int) Thread.join}
* using this time unit.
* This is a convenience method that converts time arguments into the
* form required by the {@code Thread.join} method.
*
* @param thread the thread to wait for
* @param timeout the maximum time to wait. If less than
* or equal to zero, do not wait at all.
* @throws InterruptedException if interrupted while waiting
*/
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);
}
}
}
