The P (or p) indicates a hexadecimal floating-point literal, where the significand is specified in hex.
The p is used instead of the e. The d and f suffixes that you’ve seen are orthogonal to this: both 0x1.0p+2f and 0x1.0p+2d are valid literals (one is of type float and the other is of type double).
At first glance it might seem that the 0x prefix is sufficient to identify a hex floating-point literal, so why have the Java designers chosen to change the letter from e to p? This has to do with e being a valid hex digit, so keeping it would give rise to parsing ambiguity. Consider:
0x1e+2
Is that a hex double or the sum of two integers, 0x1e and 2? When we change e to p, the ambiguity is resolved:
0x1p+2