Nikon D3300 - Manual (Page 137)

117 P, S, A, and M Modes
3
Recompose the
photograph.
Keeping the
A (L) button
pressed, recompose the
photograph and shoot.
A
Adjusting Shutter Speed and Aperture
While exposure lock is in effect, the following settings can be adjusted
without altering the metered value for exposure:
Mode Setting
Programmed auto
Shutter speed and aperture (flexible program;
0 103)
Shutter-priority auto Shutter speed
Aperture-priority auto Aperture
The metering method itself can not be changed while exposure lock is
in effect.