Java Reference
In-Depth Information
in type double :
1.0 / 3.0 is 0.3333333333333333
A double number such as 1.564E15 has two parts: the mantissa , which is
the part before the E , and the exponent , which is the part after the E .
1. In the number 1.564E15 , the mantissa is 1.564 . Mantissas can have
about 16 digits of accuracy. So, if you write 3.14159265358979324 , it
will be rounded off to 3.141592653589793 .
2. In the number 1.564E15 , the exponent is 15 . The maximum exponent is
308 . So if you write 1E309 , Java will tell you that the exponent is too
large. If you write 1E308*10 , Java will evaluate this to Infinity , and
any values that are created using it as an operand are garbage.
Java has notations for referencing the smallest positive double value and the
largest positive double value. They are:
Double.MIN_VALUE (which is 4.9E-324 )
Double.MAX_VALUE (which is 1.7976931348623157E308)
The basic operations on double values are:
unary - (negation, as in -(40E5 + 5.0) )
unary + (non-negation, as in +5.1 )
+ (addition, as in 5.0 + 6.0 )
- (subtraction, as in 4.2 - 5.1 )
* (multiplication, as in 4.0 * 6.2 )
/ (division, as in 4.5 / 3.1 )
% (remainder: 5.1 % 2.0 , which is 1.0999999999999996 )
The last operation illustrates an important point with regard to double oper-
ations: often, they give only approximations to the real result. One would think
that 2 goes into 5.1 twice, with a remainder of 1.1 . However, a roundoff error
occurs because there is only a finite amount of space for each number. Computer
arithmetic give only an approximation to the answer: 1.0999999999999996 .
The double operators have the same precedence as the corresponding int
operators.
Lesson 6-4 dis-
cusses the fact
that double
operations are
approximations.
1.1.3
Casting between int and double
If the operands of an operation (one of + , - , * , / , % ) are of type int , the opera-
tion is an int operation and produces an int . Thus, 10 / 4 evaluates to the int
value 2 . If the operands are of type double , the operation is a double operation
and produces a double . So, 5.0 * 2.2 evaluates to the double value 11.0 .
If one operand of the operation is an int and the other is a double , the int
value is converted to a double value and a double operation is performed. For
example, the expression 2+3+4*5.2 is evaluated as follows:
Lesson pages
6-2 and 6-3
discuss casting
from one type
to another.
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