Java Reference
In-Depth Information
Therelationaltype-checkingoperatorisusedtodeterminewhetheranobjectbelongs
Shift Operators
Theshiftoperatorsconsistofleftshift(
<<
),signedrightshift(
>>
),andunsignedright
shift(
>>>
).Leftshiftshiftsthebinaryrepresentationofitsleftoperandleftwardbythe
numberofpositionsspecifiedbyitsrightoperand.Eachshiftisequivalenttomultiply-
ingby2.Forexample,
2 << 3
shifts2'sbinaryrepresentationleftby3positions;the
result is equivalent to multiplying 2 by 8.
Eachofsignedandunsignedrightshiftshiftsthebinaryrepresentationofitsleftop-
erandrightwardbythenumberofpositionsspecifiedbyitsrightoperand.Eachshiftis
equivalent to dividing by 2. For example,
16 >> 3
shifts 16's binary representation
right by 3 positions; the result is equivalent to dividing 16 by 8.
The difference between signed and unsigned right shift is what happens to the sign
bitduringtheshift.Signedrightshiftincludesthesignbitintheshift,whereasunsigned
right shift ignores the sign bit. As a result, signed right shift preserved negative num-
bers,butunsignedrightshiftdoesnot.Forexample,
-4 >> 1
(theequivalentof
-4/2
)
evaluates to -2, whereas
-4 >>> 1
evaluates to 2147483646.
Tip
The shift operators are faster than multiplying or dividing by powers of 2.
Unary Minus/Plus Operators
Unary minus (
-
)and unary plus (
+
)are the simplest ofall operators. Unary minus re-
turns the negative of its operand (such as
-5
returns
-5
and
--5
returns
5
), whereas
unaryplusreturnsitsoperandverbatim(suchas
+5
returns
5
and
+-5
returns
-5
).Un-
ary plus is not commonly used, but is present for completeness.
Precedence and Associativity
Whenevaluatingacompoundexpression,Javatakeseachoperator's
precedence
(level
ofimportance)intoaccounttoensurethattheexpressionevaluatesasexpected.Forex-
ample, when presented with the expression
60+3*6
, we expect multiplication to be
performedbeforeaddition(multiplicationhashigherprecedencethanaddition),andthe
final result to be 78. We do not expect addition to occur first, yielding a result of 378.
Note
Table1-3
'srightmostcolumnpresentsavaluethatindicatesanoperator'spre-
cedence:thehigherthenumber,thehighertheprecedence.Forexample,addition'spre-
