Java Reference
In-Depth Information
15. When the variables are of type
int
, you test for equality using ==, as follows:
variable1 == variable2
When the variables are of type
String
, you test for equality using the method
equals
, as follows:
variable1.equals(variable2)
In some cases, you might want to use
equalsIgnoreCase
instead of
equals
.
16.
if
(nextWord.compareToIgnoreCase("N") < 0)
System.out.println("First half of the alphabet");
else
System.out.println("Second half of the alphabet");
17.
if
( (exam >= 60) && (programsDone >= 10) )
System.out.println("Passed");
else
System.out.println("Failed");
18.
if
( (pressure > 100) || (temperature >= 212) )
System.out.println("Emergency");
else
System.out.println("OK");
19. a.
true.
b .
true.
Note that expressions a and b mean exactly the same thing. Because
the operators
==
and
<
have higher precedence than
&&
, you do not need to
include the parentheses. The parentheses do, however, make it easier to read.
Most people find the expression in option a easier to read than the expression
in option b, even though they mean the same thing.
c .
true.
d .
true.
e .
false.
Because the value of the first subexpression,
(count == 1)
, is
false
,
you know that the entire expression is
false
without bothering to evaluate
the second subexpression. Thus, it does not matter what the values of
x
and
y
are. This is called
short-circuit evaluation
, which is what Java does.
f .
true.
Since the value of the first subexpression,
(count < 10)
, is
true
, you
know that the entire expression is
true
without bothering to evaluate the sec-
ond subexpression. Thus, it does not matter what the values of
x
and
y
are.
This is called
short-circuit evaluation
, which is what Java does.
g .
false.
Notice that the expression in g includes the expression in option f as
a subexpression. This subexpression is evaluated using short-circuit evaluation
as we described for option f. The entire expression in g is equivalent to
!( (true || (x < y)) && true )
which in turn is equivalent to
!( true && true )
, and that is equivalent to
!(true)
, which is equivalent to the final value of
false
.
