stop watch

//generate a Chronometer in xml

  <Chronometer android:id="@+id/chronometer"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:gravity="center"
     ></Chronometer>

//go to java code

//Create a object of  Chronometer
Chronometer cm=(Chronometer)findViewById(R.id.chronometer);
//start the Chronometer
cm.start();

//above code will show you stop watch on your activity

//for stop
cm.stop();
//for restart time

cm.getBase(SystemClock.elapsedRealtime());