This is due to Instant Run a new feature introduced in the studio Android 2.0, and it can be disabled as follows.
http://tools.android.com/tech-docs/instant-run
By default, Android Studio automatically restarts the current activity after performing a hot swap, and the application continues to work. To disable this option:
Open the Preferences or Preferences dialog box.
Go to build, run, deploy> Instant Run.
Uncheck "Restart" when changing the code. If automatic restart of activity is disabled, you can manually restart the current activity in the menu bar by choosing Run> Restart Activity.
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