Java Reference
In-Depth Information
1. int expression 2+3 is evaluated to yield the expression 5+4*5.2 .
2. 4 is converted to the double value 4.0 , and 4.0 * 5.2 is evaluated to
yield the expression 5 + 20.8 .
3. 5 is converted to the double value 5.0 and the addition is performed to
yield the value 25.8 .
This conversion of value from type int to type double happens automati-
cally; you do not have to worry about it. But, if you want, you can explicitly
request such a conversion, or cast as it is called in Java, by preceding the value
to be converted by the cast ( double ) . (This “type cast” is actually another oper-
ator!) Here is an example:
5/( double )2
is evaluated as follows:
1. The value 2 is cast to type double , yielding the expression 5 / 2.0 .
2. The value 5 is converted to double , yielding the expression 5.0 / 2.0 .
3. double division is performed, yielding the double value 2.5 .
Order of operations is important: to evaluate ( double )(5/2) do the divi-
sion in int arithmetic, yielding 2 , and then cast 2 to double to yield 2.0 .
You can also cast double values to type int , using ( int ) . In the expression
below, all operations are performed in double arithmetic, and then the result is
cast to an int :
( int ) ((3.5 + 4.6) / 21.2)
When casting to an int , the value is truncated toward zero, so ( int ) 3.9 eval-
uates to 3 and ( int ) -3.9 evaluates to -3 . Casts from double to int are not per-
formed automatically because they can lose information.
We say that type int is narrower than type double and type double is wider
than type int because every int value is a double but not the other way around.
A cast from int to double is called a widening cast , and a cast from double to
int is called a narrowing cast . Java performs widening casts implicitly, when
required, but narrowing casts must be explicitly given in order to be performed.
1.1.4
Type boolean and arithmetic relations
Another type that you will use frequently is boolean (named after George Boole,
a nineteenth-century mathematician who was one of the parents of logic). Type
boolean has only two values: true and false .
In Java, there are three operations on boolean values. We describe them
assuming that b1 and b2 are boolean expressions (their precedences are given
later):
Lesson
page 6-6
Negation, or not : !b1
Expression !b1 evaluates to true if b1 is false and false otherwise.
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