Converting from double to float will be a narrowing conversion. From the doc:
A narrowing primitive conversion may lose information about the overall magnitude of a numeric value and may also lose precision and range.
A narrowing primitive conversion from double to float is governed by the IEEE 754 rounding rules (ยง4.2.4). This conversion can lose precision, but also lose range, resulting in a float zero from a nonzero double and a float infinity from a finite double. A double NaN is converted to a float NaN and a double infinity is converted to the same-signed float infinity.
So it is not a good idea. If you still want it you can do it like:
double d = 3.0;
float f = (float) d;