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Issue with a double ... again

Sergey Gorovoy
Greenhorn

Joined: Jul 28, 2001
Posts: 3
I know that there are issues arising from using primitives of data type double in mathematical expressions. Somewhere in the earlier polsts it was suggested to use Math.round(a), where a is a double. However, when I execute the following:
...
double x = 27.475;
double y = 7.22;
double z = x - y;
System.out.println("x - y = " + Math.round(z));
...
I get "x - y = 20", not 20.255. If I do not use Math.round, I get 20.255000000000003. Now, how would one do the basic calculations then and get the correct result?
Manfred Leonhardt
Ranch Hand

Joined: Jan 09, 2001
Posts: 1492
Hi Sergey,
You are getting the correct result. Math.round only returns an integer. If you want to "print" out the answer formatted then you can make use of java.text.SimpleDecimalFormat.
SimpleDecimalFormat sdf = new SimpleDecimalFormat( "#.000" );
System.out.println( "x - y = " + sdf.format( z ) );
Regards,
Manfred.
Sergey Gorovoy
Greenhorn

Joined: Jul 28, 2001
Posts: 3
Thanx!
But what about the situation when the value of X and Y is being assigned dynamically, which may result in more than 3 decimal positions for Z? Is there any way to dynalically "round" the result?
 
It is sorta covered in the JavaRanch Style Guide.
 
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