android 中的 java.lang.ArrayIndexOutOfBoundsException

Question

I have an app in android(I'm running it on emulator) that receives location updates and I wanna found out the speed of the device that I track.

I do this by computing the distance between two consecutive location updates and callculating the time that I receive these updates.

And finally I wanna find the speed by dividing the distance and time(it's a rough estimation but I don't have an alternative)

And here is my problem:

I have an array of length 2 in which I put time instances....but I get

java.lang.ArrayIndexOutOfBoundsException exception at this line:

time[i]=t;

Here is my code:

public void onLocationChanged(Location loc) {
        if (loc != null) {
           try{
            float[] distance = new float[2];
            long [] time=new long[2];
            loc.distanceBetween(first_gps_lat, first_gps_lon,
                    loc.getLatitude(), loc.getLongitude(), distance);
            long t=(long)(loc.getTime()*(1e-3));
            time[i]=t;

            if(time.length==2)
            {
            var=time[1]-time[0];
                time[0]=time[1];
                i=1;
            }
            i++;
            if(contor>0)
            {
            System.out.println("Distance is:" + distance[0] + "!!!!!!");
            }

            first_gps_lat=loc.getLatitude();

            first_gps_lon=loc.getLongitude();

            contor++;
           }
           catch(Exception e)
           {
               e.printStackTrace();
           }
            latitude = (int)(first_gps_lat * 1E6);
            longitude = (int)(first_gps_lon * 1E6);



        }

---

Does someone know why I get that exception cause I can't figure out..thx

---

EDIT:

I modified to this but still the same error:

    time[i]=t;

        i=1;

            if(time[1]!=0)

            {

            var=time[1]-time[0];

                time[0]=time[1];

                i=1;
            }

Answer 1

as first you have an if statement which always will be true

long [] time=new long[2]; if(time.length==2)

and i is never set back to zero so it will keep increasing everytime the location changes so it will get out of bounds

Answer 2

Look at this snippet:

        if(time.length==2)
        {
        var=time[1]-time[0];
            time[0]=time[1];
            i=1;
        }
        i++;

After this, the value of i is 2, because time.length == 2 is always true . Next time the method gets called, the line time[i]=t; will trigger the ArrayIndexOutOfBoundsException .

Later edit:

Better not bother with an array for just two variables.

// in your activity
long oldTime, newTime, deltaTime;
oldTime = currentTimeMillis();

// in onLocationChanged()
newTime = currentTimeMillis();
deltaTime = (newTime - oldTime) / 1000; // if you need the value in seconds
oldTime = newTime;