Why float value auto incremented while sysout

user_546888 0
Viewed 214

In my application, I am using float value to hold customer score. And as per the requirement, the score may have only 5 decimal digits before the points and three digits after the points.

For example : 99999.999

But, I did not understand the strange behavior while printing float values using sysout.

Refer sample code below for more details :

public class Test {
    public static void main(String[] args) {
        float f1 = 9999.999f;
        System.out.println(f1);

        float f2 = 99999.999f;
        System.out.println(f2);
    }
}

And the Output is :

9999.999
100000.0

Here, why the value "99999.999" got auto incremented to "100000.0" while doing using sysout ? And why the same thing was not happened while using value of four decimal digits before the point i.e "9999.999" ?

Any suggestion appreciated.

primitive-types java
2 Answers

From java specifications:

float: The float data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. As with the recommendations for byte and short, use a float (instead of double) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead. Numbers and Strings covers BigDecimal and other useful classes provided by the Java platform.

To conclude if you want to save memory and you don't care about precission use float otherwise use double. More info here https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html

I suggest to use BigDecimal and use the setScale method for your case.

user_38013400

float uses 24-bit for its "mantissa" which holds all the significant digits.This means floats are usually good up to 7 significant digits. Your number is 99999.999f which has 8 significant digits.so you will lose precision after 7 digits and get this kind of errors past 7 digits.

If you try to put : double f2 = 99999.999;

You will get the right result because double uses 53-bit for it "mantissa" so it can hold about 16 digits accurately.

user_51691860
Related