Why does Oracle claim java.util.Random.nextFloat() generates 2^24 possibilities and not 2^23?

In the interval [+0, 1), there are 127•2²³ values representable in float, not 2²⁴. There is one for each combination of an exponent encoding field from 0 to 126, inclusive, with each value of 23 bits in the significand encoding field.

Every value in the form m•2⁻²⁴, with 0 ≤ m < 2²⁴, is representable. The smallest non-zero value in this form is 2⁻²⁴, which is represented with an exponent code of 103 and a significand code of 0. The mathematical exponent is the code, 103, minus the bias, 127, which equals −24, and the mathematical significand is 1.

For any such m other than zero, let b be the position number of its leading 1 bit (numbering from 0 for the low bit). Then m•2⁻²⁴ is encoded in float with an exponent code of b+103 and a significand code of m•2^{24− b}−2²⁴. For m = 0, it is encoded with all zero bits.

None of the numbers in this form are subnormal.