Multiplication of java float variable

Question

I have a piece of code as below.

String wtf = "8.40";
float ft = Float.parseFloat(wtf); //8.4
ft *= 100.0F;

the value of "ft" above is coming as 839.99994

I expected output as 840.00000 How can I correct my code so that it gives me 840.00000 as output

problem -> http://floating-point-gui.de/, solution -> use BigDecimal. — Pshemo, Oct 22 '15 at 17:44

score 0 · Answer 1 · answered Oct 22 '15 at 17:53

0

Use Double.valueOf(wtf) instead of Float.parseFloat(wtf)

answered Oct 22 '15 at 17:53

fneron · Accepted Answer · 2015-11-12T19:32:36.197

0

    String wtf = "8.40";
    double ft = Double.parseDouble(wtf); //8.4
    ft *= 100.0F;

There's is a lot of rounding when you use float. This is why you get this "unexpected" value. And I use parseDouble because the cost is less.

I suggest using BigDecimal for arithmetic and calculations.

BigDecimal BDa = new BigDecimal("8.40");
BigDecimal BDc = BDa.multiply(new BigDecimal("100.0"));

edited Nov 12 '15 at 19:32

answered Oct 22 '15 at 17:53

fneron

So why should you think this will gonna work? – mazhar islam Oct 22 '15 at 17:55
@rakeb.mazharul http://stackoverflow.com/questions/7255078/double-valueofs-vs-double-parsedouble – fneron Oct 22 '15 at 17:58
We again faced problem with this...String wtf = "9.78"; double ft = Double.parseDouble(wtf); ft *= 100.0D; // This is returning 977.999999, but it should return us 978 – Saurabh Agarwal Nov 12 '15 at 17:30
@SaurabhAgarwal Use BigDecimal instead. – fneron Nov 12 '15 at 19:23

2 Answers2