How do I display the binary representation of a float or double?

C/C++ is easy.

union ufloat {
  float f;
  unsigned u;
};

ufloat u1;
u1.f = 0.3f;

Then you just output u1.u.

Doubles just as easy.

union udouble {
  double d;
  unsigned long u;
}

because doubles are 64 bit.

Java is a bit easier: use Float.floatToRawIntBits() combined with Integer.toBinaryString() and Double.doubleToRawLongBits combined with Long.toBinaryString().