Question

can someone explain to me why the output for this:

    double y = 15/7;
    DecimalFormat first = new DecimalFormat("#.###");
    System.out.println(y); 
    String format_string = first.format(y);
    System.out.println(format_string);

Is this:

   2.0
   2

(Which is wrong)

However, when I change 15/7 to

 15.0/7.0

It gives me the correct answer

 2.142857142857143
 2.143

Explanation please?

Thank you!

Answer 1

Numbers without a dot are Integers so 15/7 is an integer-operation and the result is 2 (divistion without remainder). Afterwards it gets converted to a double but keaps it’s value of 2 (conversion after finishing the operation).

Numbers with dots are doubles in the first place so 15.0/7.0 is a double-operation and leads to the result you want to have (floating point division).