Send Integers From Ardunio to Java Program Using Serial Port

Using Arduino Interfacing w/ Software on the Computer
6

Start here. Learn about unions.

Then create a union what contains a float and a byte array:

union
{
  float f;
  byte b[4];
} u;

To write a float:

u.f = valueToSend;
Serial.write(u.b, 4);

This will require that you reassemble the bytes in the same order on the other end. Read 4 bytes, storing them in u.b[0], u.b[1], u.b[2], and u.b[4]. Then use u.f for whatever.