import java.io.PrintStream;
final class Timer{
private long startTime;
private long endTime;
public Timer() { reset(); }
public void start() {
System.gc();
startTime = System.currentTimeMillis();
}
public void end() {
System.gc();
endTime = System.currentTimeMillis();
}
public long duration() {
return (endTime - startTime);
}
public void printDuration( PrintStream out ) {
long elapsedTimeInSecond = duration() / 1000;
long remainderInMillis = duration() % 1000;
out.println("\nTotal execution time:"
+ elapsedTimeInSecond + "."
+ remainderInMillis
+ " seconds");
}
public void reset() {
startTime = 0;
endTime = 0;
}
public static void main( String[] args ) {
Timer timer = new Timer();
timer.start();
for (int i = 0; i < 500; i++) {
System.out.print("#");
}
timer.end();
timer.printDuration(System.out); }
}
在多線程環(huán)境中，線程切換由OS控制，因此兩次掐表之間可能記錄了被OS切換到的其它線程的執(zhí)行時(shí)間，這期間甚至包含其它線程的長(zhǎng)耗時(shí)I/O操作。