Java Reference
In-Depth Information
Only the equality operators
==
and
!=
are allowed to operate on boolean
values.
These operators can be combined to create a "logical
XOR
" test. The fol-
lowing code invokes
sameSign
only if both
x
and
y
have the same sign (or
zero); otherwise, it invokes
differentSign
:
if ((x < 0) == (y < 0))
sameSign();
else
differentSign();
The equality operators can also be applied to reference types. The ex-
pression
ref1==ref2
is true if the two references refer to the same object
or if both are
null
, even if the two references are of different declared
types. Otherwise, it is false.
The equality operators test for reference
identity,
not object
equivalen-
ce.
Two references are identical if they refer to the same object; two
objects are equivalent if they logically have the same value. Equivalen-
ce is tested with the
equals
method defined by
Object
, which you should
override in classes for which equivalence and identity are different.
Ob-
ject.equals
assumes an object is equal only to itself. For example, the
String
class overrides
equals
to test whether two
String
objects have the
same contentssee
Chapter 13
.
9.2.3. Logical Operators
The logical operators combine boolean expressions to yield boolean val-
ues and provide the common operations of boolean algebra:
logical
AND
&
