system.nanoTime()是不是错了？

Question

我正在编写一个FTP客户端应用程序，并在代码中的两点使用了System.nanoTime()，以秒为单位的差异返回为18，而我的程序只需要2 seconds...Check onPostExecute方法中的日志...为什么会发生这种情况，我该如何解决？

protected String doInBackground(String... urls)
{
    try
        {
        if(perflag)
            return "Not yet";
        String ipadd= ip.getText().toString();
            BufferedReader br;
            int port =Integer.parseInt(portt.getText().toString());
        while(true) {
            socket = new Socket(ipadd, port);
            //Button conn=(Button) findViewById(R.id.connectb);
            if(startflag)
            {
                starttime=System.nanoTime();
                startflag=false;
            }
            //conn.setEnabled(false);
            br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            BufferedOutputStream bo = new BufferedOutputStream(socket.getOutputStream());
            PrintWriter pw = new PrintWriter(bo, true);
            file = br.readLine();
            if (file.equals("Finished"))
            {
               // socket.close();
                Log.i("stat","above sock");
               // Thread.sleep(1000);
                //socket= new Socket(ipadd,port);
                //br= new BufferedReader(new InputStreamReader(socket.getInputStream()));
                datas=br.readLine();
                data=Double.parseDouble(datas);
                Log.i("stat",datas);
                br.close();
                socket.close();
                finflag=true;
                break;
            }
            File path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES);
            File f = new File(path, "/" + file);
            byte[] buff = new byte[1024];
            int len;

            int i=0;
            while(f.exists())
            {
                f= new File(path,"/"+"("+i+")"+file);
                i++;
            }
            pw.println("done");
            DataInputStream is = new DataInputStream(socket.getInputStream());
            FileOutputStream fos = new FileOutputStream(f);
            publishProgress(file);

            while ((len = is.read(buff)) != -1) {


                fos.write(buff, 0, len);

            }

            publishProgress(file);
        }
    }catch(NumberFormatException nfe)
    {

        runOnUiThread(new Runnable() {
            public void run() {
                Toast.makeText(MainActivity.this,"Enter a proper IP and port!",Toast.LENGTH_LONG).show();
                start();
            }
        });
        nfe.printStackTrace();

    }
    catch(java.net.UnknownHostException un)
    {
        runOnUiThread(new Runnable() {
            public void run() {
                Toast.makeText(MainActivity.this,"Enter a proper IP and port!",Toast.LENGTH_LONG).show();
                start();
            }
        });
        //Toast.makeText(MainActivity.this,"Enter a proper IP and port!",Toast.LENGTH_LONG).show();
        un.printStackTrace();
    }
    catch(java.net.NoRouteToHostException no)
    {

        runOnUiThread(new Runnable() {
            public void run() {
                Toast.makeText(MainActivity.this,"There is no active server at the specified IP and port!",Toast.LENGTH_LONG).show();
                start();
            }
        });
        no.printStackTrace();
    }
    catch(Exception e)

    {
            Log.i("error",e.getMessage());
            runOnUiThread(new Runnable() {
                public void run() {
                    Toast.makeText(MainActivity.this, "Error occurred!Try checking storage permissions or connection.", Toast.LENGTH_LONG).show();

                    start();
                }
            });
        e.printStackTrace();
    }

    endtime=System.nanoTime();
    return "Not Yet";
}
protected void onProgressUpdate(String... para)
{
    super.onProgressUpdate(para);
    trans.setText("Transfering file: "+para[0]);
}
protected void onPostExecute(String as) {
    start();

    if(finflag)
    {
        startflag=true;
        Log.i("start",String.valueOf(starttime));
        Log.i("end",String.valueOf(endtime));
        totaltime=endtime-starttime;

        Log.i("total",String.valueOf(totaltime));
        //totaltime/=100000000;
        double time=totaltime/1000000000;
        Log.i("time in secs",String.valueOf(time));
        double rate= (double)(data/time);
        Toast.makeText(MainActivity.this,"Transfer successful!",Toast.LENGTH_LONG).show();
        Toast.makeText(MainActivity.this,"Average transfer rate: "+rate+"MBps",Toast.LENGTH_LONG).show();
        finflag=false;
    }
}

Answer 1

tl;dr

Duration                          // Represent a span-of-time unattached to the timeline.
.ofNanos(                         // Represent a count of nanoseconds.
    System.nanoTime() - start     // Calculate elapsed nanoseconds.
)                                 // Returns a `Duration` object.
.toString()                       // Generates text in standard ISO 8601 format for elapsed time.

PT2.020615864S

Duration

我会使用Duration类。此类表示未附加到时间线的时间跨度，分辨率为小时-分钟-秒-纳秒。

将调用System.nanoTime返回的两个nanoseconds计数相减。将结果传递给Duration.ofNanos。

long start = System.nanoTime() ;
Thread.sleep( TimeUnit.SECONDS.toMillis( 2 ) ); 
long stop = System.nanoTime() ;

Duration d = Duration.ofNanos( stop - start ) ;

System.out.println( d ) ;

请参阅此code run live at IdeOne.com。

PT2.020615864S

实际上，在实际代码中，我们需要处理Thread sleep被中断(唤醒)。

long start = System.nanoTime();
try
{
    Thread.sleep( TimeUnit.SECONDS.toMillis( 2 ) ); 
} catch ( InterruptedException e )
{
    e.printStackTrace();
}
long stop = System.nanoTime();

Duration d = Duration.ofNanos( stop - start );

System.out.println( d );