Answer by Mr.Goomer for Detect when user enter circle

So finally thanks to @Axiumin ,I did this:

@Overridepublic void onLocationChanged(Location location) {    userLocationMarker.setPosition(new LatLng(location.getLatitude(), location.getLongitude()));    Location userLocation = new Location("userLocation");    userLocation.setLatitude(location.getLatitude());    userLocation.setLongitude(location.getLongitude());    Location circleLocation = new Location("circleLocation");    circleLocation.setLatitude(circle.getCenter().latitude);    circleLocation.setLongitude(circle.getCenter().longitude);    float distance = userLocation.distanceTo(circleLocation);    if (distance <= 70){ // If distance is less than 70 Meters    }}