Rounded result even casting to float

Question

I don't know why java is rounding result. I used casting to float, I was adding '.0f'. Nothing want to work. I know that double is better for dividing but I don't need very precision result.

int A = Integer.parseInt(listBytesAnsw.get(2), 16); //ex. 18
int B = Integer.parseInt(listBytesAnsw.get(3), 16); //ex. 226
float rpm = (float) (A*255+B)/4; //Ans=1204 wrong, should be 1203.75

float rpm = (float) (A*255.0f+B)/4.0f; //dont work still 1204

`/4` is an **integer divison**, no matter if you cast the upper part of the fraction to a flow. You should divide by `4.0f` to get the result you want. — Maximilian Gerhardt, Dec 23 '15 at 19:26
No, your example is wrong. rpm = (A*255+B)/4.0 = (18*255 + 226)/4.0 = 4816 / 4.0 = 1204.0 Using the example values, the result *is* 1204. — Maximilian Gerhardt, Dec 23 '15 at 19:35
Ohh, I dont know where from I get this example. I didn't check it. My bad — GarryMoveOut, Dec 23 '15 at 19:47
This is correct and I never stated otherwise. I just noted that `float / int` as in *integer divison* by 4 is what's happening here, but OP wants `float / float` (well, `int/float` actually, there's no float precision in the numerator). — Maximilian Gerhardt, Dec 23 '15 at 20:26

luksch · Accepted Answer · 2015-12-23T20:09:44.087

-1

The result you get is to be expected. After all:

255*226 = 4816
4816 / 4 = 1204

Of course, rounding and then casting would not work in case you have indeed a non-integer result. So look at the following code

System.out.println("(float)(7/4)=" + ((float)(7/4)));
System.out.println("(float)7/4=" + ((float)7/4));
System.out.println("(7+0.0f)/4=" + ((7+0.0f)/4));
System.out.println("7/(4+0.0f)=" + (7/(4+0.0f)));

results in

(float)(7/4)=1.0
(float)7/4=1.75
(7+0.0f)/4=1.75
7/(4+0.0f)=1.75

The first does not work as you found out. But either of the other solutions works.

edited Dec 23 '15 at 20:09

answered Dec 23 '15 at 19:38

luksch

11,497
6
38
53

No need for the addition. (float)(7) / 4 = 1.75 – FredK Dec 23 '15 at 20:15
Already added. you don't the brackets around the 7 either – luksch Dec 23 '15 at 20:16

Rounded result even casting to float

1 Answers1