Java Reference
In-Depth Information
The bitwise AND and OR operators (
&
and
|
) lack short-circuit behavior. Similar to
most Java operators, they evaluate both operands. They return the same Boolean results
as
&&
and
||
respectively,butcanhavedifferentoveralleffectsdependingonthepresence
or absence of side effects in the second operand.
Consequently, either the
&
or the
&&
operator can be used when performing Boolean
logic. However, there are times when the short-circuiting behavior is preferred and other
times when the short-circuiting behavior causes subtle bugs.
Noncompliant Code Example (Improper
&
)
This noncompliant code example, derived from Flanagan [Flanagan 2005], has two vari-
ables with unknown values. The code must validate its data, and then check whether
ar-
ray[i]
is a valid index.
int array[]; // May be null
int i; // May be an invalid index for array
if (array != null & i >= 0 &
i < array.length & array[i] >= 0) {
// Use array
} else {
// Handle error
}
This code can fail as a result of the same errors it is trying to prevent. When
array
is
NULL
or
i
is not a valid index, the reference to
array
and
array[i]
will cause either
a
NullPointerException
or an
ArrayIndexOutOfBoundsException
to be thrown. The
exception occurs because the
&
operator fails to prevent evaluation of its right operand,
even when evaluation of its left operand proves that the right operand is inconsequential.
Compliant Solution (Use
&&
)
Thiscompliantsolutionmitigatestheproblembyusing
&&
,whichcausestheevaluationof
the conditional expression to terminate immediately if any of the conditions fail, thereby
preventing a runtime exception:
int array[]; // May be null
int i; // May be an invalid index for array
if (array != null && i >= 0 &&
