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学习java的经典书籍

produces a one in the output bit if one or the other input bit is a one, but
not both. The bitwise NOT<A NAME="Index165"></A>
(~, also called the ones complement operator<A NAME="Index166"></A><A NAME="Index167"></A>)
is a unary operator;<A NAME="Index168"></A><A NAME="Index169"></A>
it takes only one argument. (All other bitwise operators are binary operators.<A NAME="Index170"></A><A NAME="Index171"></A>)
Bitwise NOT produces the opposite of the input bit &#8211; a one if the input
bit is zero, a zero if the input bit is one.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
bitwise operators and logical operators use the same characters, so it is
helpful to have a mnemonic device to help you remember the meanings: since bits
are &#8220;small,&#8221; there is only one character in the bitwise operators.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Bitwise
operators can be combined with the = sign to unite the operation and
assignment: &amp;=<A NAME="Index172"></A>,
|=<A NAME="Index173"></A>
and ^=<A NAME="Index174"></A>
are all legitimate. (Since ~ is a unary operator it cannot be combined with the
= sign.)
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>boolean</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
type is treated as a one-bit value so it is somewhat different. You can perform
a bitwise AND, OR and XOR, but you can&#8217;t perform a bitwise NOT
(presumably to prevent confusion with the logical NOT). For 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>boolean</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">s
the bitwise operators have the same effect as the logical operators except that
they do not short circuit. Also, the bitwise operators on 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>boolean</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">s
gives you a XOR logical operator that is not included under the list of
&#8220;logical&#8221; operators. You&#8217;re prevented from using 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>boolean</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">s
in shift expressions, which is described next.
</FONT><a name="_Toc375545255"></a><a name="_Toc408018456"></a><P></DIV>
<A NAME="Heading112"></A><H3 ALIGN=LEFT>
Shift
operators<A NAME="Index175"></A><A NAME="Index176"></A></H3>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
shift operators also manipulate bits. They can be used solely with primitive,
integral types. The left-shift operator (
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>&lt;&lt;</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">)<A NAME="Index177"></A><A NAME="Index178"></A>
produces the operand to the left of the operator shifted to the left by the
number of bits specified after the operator (inserting zeroes at the
lower-order bits). The signed right-shift operator (
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>&gt;&gt;</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">)<A NAME="Index179"></A><A NAME="Index180"></A>
produces the operand to the left of the operator shifted to the right by the
number of bits specified after the operator. The signed right shift 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>&gt;&gt;
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">uses
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>sign
extension
</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">:
if the value is positive, zeroes are inserted at the higher-order bits; if the
value is negative, ones are inserted at the higher-order bits. Java has also
added the unsigned right shift 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>&gt;&gt;&gt;,
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">which</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">uses
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>zero
extension
</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">:
regardless of the sign, zeroes are inserted at the higher-order bits.
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>
</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">This
operator does not exist in C or C++.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">If
you shift a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>char</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>byte,</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
or 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>short</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
it will be promoted to 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>int</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
before the shift takes place, and the result will be an 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>int</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
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 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>int</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
If you&#8217;re operating on a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>long</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>long</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
will be the result. Only the six low-order bits of the right-hand side will be
used so you can&#8217;t shift more than the number of bits in a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>long</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
There is a problem, however, with the unsigned right shift. If you use it with 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>byte</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
or 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>short</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
you might not get the correct results. (It&#8217;s broken in <A NAME="Index181"></A>Java
1.0 and Java 1.1.<A NAME="Index182"></A>)
These are promoted to 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>int</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and right shifted, but the zero extension does 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>not</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
occur, so you get 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>-1</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
in those cases. The following example can be used to test your implementation:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: 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 &gt;&gt;&gt;= 10;
    System.out.println(i);
    <font color="#0000ff">long</font> l = -1;
    l &gt;&gt;&gt;= 10;
    System.out.println(l);
    <font color="#0000ff">short</font> s = -1;
    s &gt;&gt;&gt;= 10;
    System.out.println(s);
    <font color="#0000ff">byte</font> b = -1;
    b &gt;&gt;&gt;= 10;
    System.out.println(b);
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Shifts
can be combined with the equal sign (
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>&lt;&lt;=</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
or 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>&gt;&gt;=</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
or 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>&gt;&gt;&gt;=</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">)<A NAME="Index183"></A><A NAME="Index184"></A>.
The lvalue is replaced by the lvalue shifted by the rvalue.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Here&#8217;s
an example that demonstrates the use of all the operators involving bits:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: 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("-1", -1);
    pBinInt("+1", +1);
    <font color="#0000ff">int</font> maxpos = 2147483647;
    pBinInt("maxpos", maxpos);
    <font color="#0000ff">int</font> maxneg = -2147483648;
    pBinInt("maxneg", maxneg);
    pBinInt("i", i);
    pBinInt("~i", ~i);
    pBinInt("-i", -i);
    pBinInt("j", j);
    pBinInt("i &amp; j", i &amp; j);
    pBinInt("i | j", i | j);
    pBinInt("i ^ j", i ^ j);
    pBinInt("i &lt;&lt; 5", i &lt;&lt; 5);
    pBinInt("i &gt;&gt; 5", i &gt;&gt; 5);
    pBinInt("(~i) &gt;&gt; 5", (~i) &gt;&gt; 5);
    pBinInt("i &gt;&gt;&gt; 5", i &gt;&gt;&gt; 5);
    pBinInt("(~i) &gt;&gt;&gt; 5", (~i) &gt;&gt;&gt; 5);

    <font color="#0000ff">long</font> l = rand.nextLong();
    <font color="#0000ff">long</font> m = rand.nextLong();
    pBinLong("-1L", -1L);
    pBinLong("+1L", +1L);
    <font color="#0000ff">long</font> ll = 9223372036854775807L;
    pBinLong("maxpos", ll);
    <font color="#0000ff">long</font> lln = -9223372036854775808L;
    pBinLong("maxneg", lln);
    pBinLong("l", l);
    pBinLong("~l", ~l);
    pBinLong("-l", -l);
    pBinLong("m", m);
    pBinLong("l &amp; m", l &amp; m);
    pBinLong("l | m", l | m);
    pBinLong("l ^ m", l ^ m);
    pBinLong("l &lt;&lt; 5", l &lt;&lt; 5);
    pBinLong("l &gt;&gt; 5", l &gt;&gt; 5);
    pBinLong("(~l) &gt;&gt; 5", (~l) &gt;&gt; 5);
    pBinLong("l &gt;&gt;&gt; 5", l &gt;&gt;&gt; 5);
    pBinLong("(~l) &gt;&gt;&gt; 5", (~l) &gt;&gt;&gt; 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="#0000ff">int</font>: " + i + ", binary: ");
    System.out.print("   ");
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> j = 31; j &gt;=0; j--)
      <font color="#0000ff">if</font>(((1 &lt;&lt; j) &amp;  i) != 0)
        System.out.print("1");
      <font color="#0000ff">else</font>
        System.out.print("0");
    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="#0000ff">long</font>: " + l + ", binary: ");
    System.out.print("   ");
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 63; i &gt;=0; i--)
      <font color="#0000ff">if</font>(((1L &lt;&lt; i) &amp; l) != 0)
        System.out.print("1");
      <font color="#0000ff">else</font>
        System.out.print("0");
    System.out.println();
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
two methods at the end, 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>pBinInt(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>pBinLong(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
take an 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>int</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
or a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>long</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
respectively,