If this is the error message:
Car.java:25: error: constructor Car in class Car cannot be applied to given types;
Car myFastCar = new Car(55.5); /*_NOW HERE I MADE AN OBJECT USING CONSTRUCTER CALLING_AND PASS FLOAT TYPE ARGUMENT IN IT BUT IT GIVES ME AN ERROR HERE ON 55.5...WHEN I PASS INTEGER TYPE IT DOESNT GIVE ME ERROR .WHY?**/
reason: argument mismatch; possible lossy conversion from double to float
Then yes, that's an error, and to find out why you're getting it, read it - it says why!
If not, perhaps I'm getting some other error because I don't have the full code, what you posted isn't a complete example (also it's missing a forward slash and two closing curly braces)