java中是否有用于测量执行时间的命令？

Question

java中是否有用于测量执行时间的命令

差不多

System.out.println(execution.time);

在代码的最后

Answer 1

以下是关于如何做到这一点的complete and little modified example：

public class ExecutionTimer {
  private long start;
  private long end;

  public ExecutionTimer() {
    reset();
    start = System.currentTimeMillis();
  }

  public void end() {
    end = System.currentTimeMillis();
  }

  public long duration(){
    return (end-start);
  }

  public void reset() {
    start = 0;  
    end   = 0;
  }

  public static void main(String s[]) {
    // simple example
    ExecutionTimer t = new ExecutionTimer();
    for (int i = 0; i < 80; i++){
System.out.print(".");
}
    t.end();
    System.out.println("\n" + t.duration() + " ms");
  }
}

Answer 2

使用ThreadMXBean获取更详细的计时信息：

public class Timer {

  static { 
    // needed to request 1ms timer interrupt period 
    // http://discuss.joelonsoftware.com/default.asp?joel.3.642646.9
    Thread thread = new Thread(new Runnable() {
      @Override
      public void run() {
        try {
          Thread.sleep(Integer.MAX_VALUE);  (Windows NT)
        } catch (InterruptedException ignored) {
        }
      }
    });
    thread.setName("Timer");
    thread.setDaemon(true);
    thread.start();
  }

  private final ThreadMXBean threadMX = ManagementFactory.getThreadMXBean();
  private final long elapsedStart;
  private final long cpuStart;
  private final long userStart;

  public Timer() {
    cpuStart = threadMX.getCurrentThreadCpuTime();
    userStart = threadMX.getCurrentThreadUserTime();
    elapsedStart = System.nanoTime();
  }

  public void times() {
    long elapsed = elapsedStart - System.nanoTime();
    long cpu = cpuStart - threadMX.getCurrentThreadCpuTime();
    long user = userStart - threadMX.getCurrentThreadUserTime();
    System.out.printf("elapsed=%-8.3f cpu=%-8.3f user=%-8.3f [seconds]", 
            elapsed/1.0e9, cpu/1.0e9, user/1.0e9);
  }
}

Answer 3

您可以运行一个探查器，或者使用两个调用的差异来System.currentTimeMillis()

像这样：

long start = System.currentTimeMillis();
....
doSomething();
....
long end = System.currentTimeMillis();

System.out.println("Execution time was "+(end-start)+" ms.");

Answer 4

最简单的方法就是使用这个系统。currentTimeMillis（）在代码执行之前和之后。Joda Time有更复杂的版本：http://joda-time.sourceforge.net/

Answer 5

如果您想了解更多有关测量内容的详细信息，我强烈建议您使用JMX，尤其是ThreadMXBean:http://download.oracle.com/javase/6/docs/api/java/lang/management/ThreadMXBean.html

代码示例：

ThreadMXBean bean = ManagementFactory.getThreadMXBean( );
if (bean.isCurrentThreadCpuTimeSupported()) {
    long cpuTime = bean.getCurrentThreadCpuTime( );
}
long userTime = bean.getCurrentThreadUserTime( );

这里有一个完整的代码示例说明： http://nadeausoftware.com/articles/2008/03/java_tip_how_get_cpu_and_user_time_benchmarking