Help with float numbers in Java

Question

Hi, Could anyone please me why the output of the following programme is not " different different"?

public static void main(String[] args)
{

float f1=3.2f;
float f2=6.5f;

if(f1==3.2)
System.out.println("same");
else
System.out.println("different");

if(f2==6.5)
System.out.println("same");
else
System.out.println("different");
}

o/p :different same

Answer 1

This can help understand

Answer 2

Because 3.2f is a float value and 3.2 is a double value. Floating point numbers are always slightly inaccurate because binary representation cannot implement them accurately, so comparing them for exact equality is a bad idea. Particularly comparing floats with doubles. Expressions such as 3.2f == 3.2f are usually okay, but even those can fail in some languages, e.g. if they represent numbers in registers more accurately than in memory.

Answer 3

"3.2f" is a of type float. "3.2" is of type double.

Answer 4

Also, I think anything with a decimal defaults into a double, so when you do a comparison, you have to add 'f' as well like if(f2==6.4f).

Answer 5

Because 3.2 is not representable exactly as floating point number and 6.5 is (hint: 6.5 = 13 * 2^(-1)), as well as the fact that 3.2 is a double literal but 3.2f is a float literal.

Answer 6

try not to compare the floating type value.

Answer 7

6.5 has a finite binary representation: 110.1

Any floating type with at least 4 significant bits can represent this number perfectly.

110.100000000000000000000 (float)
= 6.5

110.10000000000000000000000000000000000000000000000000 (double)
= 6.5

3.2 on the other hand has an infinite binary representation: 101.0011001100110011...

float and double don't have infinite precision and thus can only approximate this number :(

101.001100110011001100110 (float)
= 3.2000000476837158203125

101.00110011001100110011001100110011001100110011001101 (double)
= 3.20000000000000017763568394002504646778106689453125

As you can clearly see, these numbers are not the same!