Errors are posted to the registered CameraListeners callback:

@Override
public void onCameraError(CameraException error) {
    // Got error!
};

You are supposed to inspect the CameraException object as it contains useful information about what happened and what should be done, if anything. All things that fail can end up throwing this exception, which includes temporary actions like taking a picture, or functional actions like starting the camera preview.

Unrecoverable errors

You can exclude unrecoverable errors using CameraException.isUnrecoverable(). If this function returns true, at this point the camera has been released and it is likely showing a black preview. The operation can’t go on.

You can try to call camera.start() again, but that’s not guaranteed to work. For example, the camera sensor might be in use by another application, so there’s nothing we could do.

Other errors

For more fine grained control over what happened, inspect the reason using CameraException.getReason(). This will return one of the CameraException.REASON_ constants:

Constant Description Unrecoverable
REASON_UNKNOWN Unknown error. No other info available. No
REASON_FAILED_TO_CONNECT Failed to connect to the camera service. Yes
REASON_FAILED_TO_START_PREVIEW Failed to start the camera preview. Yes
REASON_DISCONNECTED Camera was forced to disconnect by the system. Yes
REASON_PICTURE_FAILED Could not take a picture or picture snapshot. No
REASON_VIDEO_FAILED Could not take a video or video snapshot. No
REASON_NO_CAMERA Could not find a camera for this Facing value. You can try another. No