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<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">If you shift a <B>char</B>, <B>byte,</B>
or <B>short</B>, it will be promoted to <B>int</B> before the shift takes place,
and the result will be an <B>int</B>. Only the five low-order bits of the
right-hand side will be used. This prevents you from shifting more than the
number of bits in an <B>int</B>. If you’re operating on a <B>long</B>,
you’ll get a <B>long</B> result. Only the six low-order bits of the
right-hand side will be used so you can’t shift more than the number of
bits in a <B>long</B>.
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<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Shifts can be combined with the equal
sign (<B><<=</B> or <B>>>=</B> or
<B>>>>=</B>)<A NAME="Index299"></A><A NAME="Index300"></A>. The lvalue
is replaced by the lvalue shifted by the rvalue. There is a problem, however,
with the unsigned right shift combined with assignment. If you use it with
<B>byte</B> or <B>short</B> you don’t get the correct results. Instead,
these are promoted to <B>int</B> and right shifted, but then truncated as they
are assigned back into their variables, so you get <B>-1</B> in those cases. The
following example demonstrates this:
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<BLOCKQUOTE><FONT SIZE = "+1"><PRE><font color=#009900>//: c03:URShift.java</font>
<font color=#009900>// Test of unsigned right shift.</font>
<font color=#0000ff>public</font> <font color=#0000ff>class</font> URShift {
<font color=#0000ff>public</font> <font color=#0000ff>static</font> <font color=#0000ff>void</font> main(String[] args) {
<font color=#0000ff>int</font> i = -1;
i >>>= 10;
System.out.println(i);
<font color=#0000ff>long</font> l = -1;
l >>>= 10;
System.out.println(l);
<font color=#0000ff>short</font> s = -1;
s >>>= 10;
System.out.println(s);
<font color=#0000ff>byte</font> b = -1;
b >>>= 10;
System.out.println(b);
b = -1;
System.out.println(b>>>10);
}
} <font color=#009900>///:~</font></PRE></FONT></BLOCKQUOTE>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">In the last line, the resulting value is
not assigned back into <B>b</B>, but is printed directly and so the correct
behavior occurs.
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<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Here’s an example that demonstrates
the use of all the operators involving bits:</FONT><BR></P></DIV>
<BLOCKQUOTE><FONT SIZE = "+1"><PRE><font color=#009900>//: c03:BitManipulation.java</font>
<font color=#009900>// Using the bitwise operators.</font>
<font color=#0000ff>import</font> java.util.*;
<font color=#0000ff>public</font> <font color=#0000ff>class</font> BitManipulation {
<font color=#0000ff>public</font> <font color=#0000ff>static</font> <font color=#0000ff>void</font> main(String[] args) {
Random rand = <font color=#0000ff>new</font> Random();
<font color=#0000ff>int</font> i = rand.nextInt();
<font color=#0000ff>int</font> j = rand.nextInt();
pBinInt(<font color=#004488>"-1"</font>, -1);
pBinInt(<font color=#004488>"+1"</font>, +1);
<font color=#0000ff>int</font> maxpos = 2147483647;
pBinInt(<font color=#004488>"maxpos"</font>, maxpos);
<font color=#0000ff>int</font> maxneg = -2147483648;
pBinInt(<font color=#004488>"maxneg"</font>, maxneg);
pBinInt(<font color=#004488>"i"</font>, i);
pBinInt(<font color=#004488>"~i"</font>, ~i);
pBinInt(<font color=#004488>"-i"</font>, -i);
pBinInt(<font color=#004488>"j"</font>, j);
pBinInt(<font color=#004488>"i & j"</font>, i & j);
pBinInt(<font color=#004488>"i | j"</font>, i | j);
pBinInt(<font color=#004488>"i ^ j"</font>, i ^ j);
pBinInt(<font color=#004488>"i << 5"</font>, i << 5);
pBinInt(<font color=#004488>"i >> 5"</font>, i >> 5);
pBinInt(<font color=#004488>"(~i) >> 5"</font>, (~i) >> 5);
pBinInt(<font color=#004488>"i >>> 5"</font>, i >>> 5);
pBinInt(<font color=#004488>"(~i) >>> 5"</font>, (~i) >>> 5);
<font color=#0000ff>long</font> l = rand.nextLong();
<font color=#0000ff>long</font> m = rand.nextLong();
pBinLong(<font color=#004488>"-1L"</font>, -1L);
pBinLong(<font color=#004488>"+1L"</font>, +1L);
<font color=#0000ff>long</font> ll = 9223372036854775807L;
pBinLong(<font color=#004488>"maxpos"</font>, ll);
<font color=#0000ff>long</font> lln = -9223372036854775808L;
pBinLong(<font color=#004488>"maxneg"</font>, lln);
pBinLong(<font color=#004488>"l"</font>, l);
pBinLong(<font color=#004488>"~l"</font>, ~l);
pBinLong(<font color=#004488>"-l"</font>, -l);
pBinLong(<font color=#004488>"m"</font>, m);
pBinLong(<font color=#004488>"l & m"</font>, l & m);
pBinLong(<font color=#004488>"l | m"</font>, l | m);
pBinLong(<font color=#004488>"l ^ m"</font>, l ^ m);
pBinLong(<font color=#004488>"l << 5"</font>, l << 5);
pBinLong(<font color=#004488>"l >> 5"</font>, l >> 5);
pBinLong(<font color=#004488>"(~l) >> 5"</font>, (~l) >> 5);
pBinLong(<font color=#004488>"l >>> 5"</font>, l >>> 5);
pBinLong(<font color=#004488>"(~l) >>> 5"</font>, (~l) >>> 5);
}
<font color=#0000ff>static</font> <font color=#0000ff>void</font> pBinInt(String s, <font color=#0000ff>int</font> i) {
System.out.println(
s + <font color=#004488>", int: "</font> + i + <font color=#004488>", binary: "</font>);
System.out.print(<font color=#004488>" "</font>);
<font color=#0000ff>for</font>(<font color=#0000ff>int</font> j = 31; j >=0; j--)
<font color=#0000ff>if</font>(((1 << j) & i) != 0)
System.out.print(<font color=#004488>"1"</font>);
<font color=#0000ff>else</font>
System.out.print(<font color=#004488>"0"</font>);
System.out.println();
}
<font color=#0000ff>static</font> <font color=#0000ff>void</font> pBinLong(String s, <font color=#0000ff>long</font> l) {
System.out.println(
s + <font color=#004488>", long: "</font> + l + <font color=#004488>", binary: "</font>);
System.out.print(<font color=#004488>" "</font>);
<font color=#0000ff>for</font>(<font color=#0000ff>int</font> i = 63; i >=0; i--)
<font color=#0000ff>if</font>(((1L << i) & l) != 0)
System.out.print(<font color=#004488>"1"</font>);
<font color=#0000ff>else</font>
System.out.print(<font color=#004488>"0"</font>);
System.out.println();
}
} <font color=#009900>///:~</font></PRE></FONT></BLOCKQUOTE>
<DIV ALIGN="LEFT"><P><A NAME="Index301"></A><FONT FACE="Georgia">The two methods at
the end, <B>pBinInt( )</B> and <B>pBinLong( )</B> take an <B>int</B>
or a <B>long</B>, respectively, and print it out in binary format along with a
descriptive string. You can ignore the implementation of these for now.
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<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">You’ll note the use of
<B>System.out.print( )</B> instead of <B>System.out.println( )</B>.
The <B>print( )</B> method does not emit a new line, so it allows you to
output a line in pieces.
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<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">As well as demonstrating the effect of
all the bitwise operators for <B>int</B> and <B>long</B>, this example also
shows the minimum, maximum, +1 and -1 values for <B>int</B> and <B>long</B> so
you can see what they look like. Note that the high bit represents the sign: 0
means positive and 1 means negative. The output for the <B>int</B> portion looks
like this:</FONT><BR></P></DIV>
<BLOCKQUOTE><FONT SIZE = "+1"><PRE>-1, <font color=#0000ff>int</font>: -1, binary:
11111111111111111111111111111111
+1, <font color=#0000ff>int</font>: 1, binary:
00000000000000000000000000000001
maxpos, <font color=#0000ff>int</font>: 2147483647, binary:
01111111111111111111111111111111
maxneg, <font color=#0000ff>int</font>: -2147483648, binary:
10000000000000000000000000000000
i, <font color=#0000ff>int</font>: 59081716, binary:
00000011100001011000001111110100
~i, <font color=#0000ff>int</font>: -59081717, binary:
11111100011110100111110000001011
-i, <font color=#0000ff>int</font>: -59081716, binary:
11111100011110100111110000001100
j, <font color=#0000ff>int</font>: 198850956, binary:
00001011110110100011100110001100
i & j, <font color=#0000ff>int</font>: 58720644, binary:
00000011100000000000000110000100
i | j, <font color=#0000ff>int</font>: 199212028, binary:
00001011110111111011101111111100
i ^ j, <font color=#0000ff>int</font>: 140491384, binary:
00001000010111111011101001111000
i << 5, <font color=#0000ff>int</font>: 1890614912, binary:
01110000101100000111111010000000
i >> 5, <font color=#0000ff>int</font>: 1846303, binary:
00000000000111000010110000011111
(~i) >> 5, <font color=#0000ff>int</font>: -1846304, binary:
11111111111000111101001111100000
i >>> 5, <font color=#0000ff>int</font>: 1846303, binary:
00000000000111000010110000011111
(~i) >>> 5, <font color=#0000ff>int</font>: 132371424, binary:
00000111111000111101001111100000</PRE></FONT></BLOCKQUOTE>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">The binary representation of the numbers
is referred to as <A NAME="Index302"></A><A NAME="Index303"></A><I>signed
two’s complement</I>.
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</FONT><A NAME="_Toc375545256"></A><A NAME="_Toc481064550"></A><BR></P></DIV>
<A NAME="Heading139"></A><FONT FACE = "Verdana"><H3 ALIGN="LEFT">
Ternary if-else
operator<A NAME="Index304"></A><A NAME="Index305"></A><A NAME="Index306"></A></H3></FONT>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">This operator is unusual because it has
three operands. It is truly an operator because it produces a value, unlike the
ordinary if-else statement that you’ll see in the next section of this
chapter<A NAME="Index307"></A>. The expression is of the form:
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<BLOCKQUOTE><FONT SIZE = "+1"><PRE><font color=#0000ff>boolean</font>-exp ? value0 : value1</PRE></FONT></BLOCKQUOTE>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">If <I>boolean-exp</I> evaluates to
<B>true</B>, <I>value0</I> is evaluated and its result becomes the value
produced by the operator. If <I>boolean-exp</I> is <B>false</B>, <I>value1</I>
is evaluated and its result becomes the value produced by the operator.
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<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Of course, you could use an ordinary
<B>if-else </B>statement (described later), but the ternary operator is much
terser. Although C (where this operator originated) prides itself on being a
terse language, and the ternary operator might have been introduced partly for
efficiency, you should be somewhat wary of using it on an everyday
basis—it’s easy to produce unreadable code.
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<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">The conditional operator can be used for
its side effects or for the value it produces, but in general you want the value
since that’s what makes the operator distinct from the <B>if-e⌨️ 快捷键说明
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