Question

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Strange floating-point behaviour in a Java program

I came across this weird phenomenon in Java. Try this statement in a Java program:

System.out.print(4.0-3.1);

The output will be 0.8999999

Why does this happen? And how can it be changed?

Answer 1

This is a typical floating point result runded.

You get different results from Float and Double :

System.out.println(4.0f-3.1f);
System.out.println(4.0d-3.1d);

Output:

0.9000001
0.8999999999999999

This is because 0.1 cannot be represented evenly in base 2, and cause a loss of precision. For example :

System.out.println(2.0f-1.9f);
System.out.println(2.0d-1.9d);

Should both return 0.1 but in fact will output :

0.100000024
0.10000000000000009