Truncation Error when I try to create a Array of values

Question

I want a create a array of values with a interval of 0.2 I used the code :

public class TrialCode {

public static void main(String[] args) {

    float a = -1.0f, b = 0.2f;

    for (int i = 0; i <10; i++) {
        a = a + b;
        System.out.println(a);

    }

}

}

Now the output that i am getting is :

-0.8
-0.6
-0.40000004
-0.20000003
-2.9802322E-8
0.19999997
0.39999998
0.59999996
0.79999995
0.99999994

whereas the output I want is

-0.8, -0.6, -0.4, -0.2, 0, 0.2, 0.4, 0.6, 0.8, 1.0

What should I do ?

score 5 · Answer 1 · answered Feb 08 '14 at 08:16

5

Floating point numbers only work up to a certain precision. For float it is 6-7 significant digits, for double it is 15-16 significant digits. And due to the binary representation simple decimal fractions like 0.1 cannot be represented exactly.

You can round the output to get the results you want:

System.out.printf("%.1f", a);

answered Feb 08 '14 at 08:16

Henry

42,982
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I was about to answer this. – Grijesh Chauhan Feb 08 '14 at 08:17
does java has printf or it might be println ? – ItayB Feb 08 '14 at 08:18
1

@ItayB yes to [use format string you need to use printf](http://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html) – Grijesh Chauhan Feb 08 '14 at 08:20
1

@ItayB printf is available since Java 1.5 – Henry Feb 08 '14 at 08:20
@ItayB Note in print **f** , `f` stands for 'format' (but not for file) – Grijesh Chauhan Feb 08 '14 at 08:21
cool! I have learned here something new! thanks! – ItayB Feb 08 '14 at 08:21
Yes, but this approach will eventually fail, if you add 0.2 enough times. You're only hiding the effect, not removing it. A better solution would be to use a `BigDecimal`. – Dawood ibn Kareem Feb 08 '14 at 08:30
@DavidWallace That really depends on the application. `BigDecimal` will show the same problems for other simple increments like one third. Moreover it is much slower. – Henry Feb 08 '14 at 08:40

Chris Martin · Accepted Answer · 2014-02-08T08:32:55.110

If you don't want floating-point arithmetic, then don't use floating-point types. Float and Double aren't the only non-integral Numbers in the Java core library. What you're doing calls for BigDecimal.

import java.math.BigDecimal;

public class TrialCode {

    public static void main(String[] args) {

        BigDecimal a = new BigDecimal("-1.0");
        BigDecimal b = new BigDecimal("0.2");

        for (int i = 0; i < 10; i++) {
            a = a.add(b);
            System.out.println(a);
        }
    }
}

score 0 · Answer 3 · answered Feb 08 '14 at 08:19

0

You can use something like

new DecimalFormat("#.#").format(0.19999997); //"0.2"

answered Feb 08 '14 at 08:19

rocketboy

9,573
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Truncation Error when I try to create a Array of values

3 Answers3