如果对char,byte,或者 short进行了移位,它们会被先转换成 int,因此运算的结果也就成了int。运算符的右边那这个数,只有低五 位有效。这是为了防止移位的位数超过int的位数。如果操作数是 long,那么结果也是long。这时运算符右边那个数的低六位有效,这 样移位的位数就不会超过long的位数。 移位可以同等号连起来用(<<=或>>=或>>=)。Vaue移了 rvalue位之后,会被再存进laue。但是不带符号的右移位和等号连用 的时候会有一个问题。如果操作数是byte或 short的话,结果就不对 了。它们会被先提升到int再进行右移,但是重新赋值给原先的变量时, 这个值就得被截短,所以移来移去结果都是-1。下面这段程序就演示了 这个效果 // c03: URShif // Test of unsigned right shift import com. bruceeckel. simpletest public class URShift Test o public static void main(String[] args)t int 1 System. out. println(1 >>>=10) System. out. println(s >>>=10)i System. out. println(b >>>=10)i System. out. println (b>>>10)i monitor. expect (new string[] t 4194303", 18014398509481983 4194303 最后一次移位,没有把运算结果赋还给b而是直接打印出来了,所以它 才是正确的 下面这段例程演示了所有与位操作相关的运算符的用法 // c03: BitManipulation. java import com. bruceeckel. simpletest. import java. util.*i public class BitManipulation t static Test monitor new Test(i 第16页共48页
shhgs@wgqqh.com 16 ✁ ✂ 48 ✁ ÄÅ¥ char byte sh ort ( ,g AWºT/= in t æò (OÅ[ , in t (1Y ×" ómQâ mØ ,d+g("{^ in t ("ÄÅ1" l on g YZOÅ[l on g 1Y×"(QomØ ¦g(" Xº{^l on g (" gÝE-Sa9Q(< < = > > = > > =)l val ue g, rval ue u ºTÁ(l val ueX S(g-Sa (Mºm3×cdÄÅ1" byte sh ort ( OÅ X¥ ,AWºT/Mg in t Á( g K~L¬å/( ×L T{F DEgQg+OÅÆ -1¶ â , ×ØÅ0 //: c03:URShift.java // Test of unsigned right shift. import com.bruceeckel.simpletest.*; public class URShift { static Test monitor = new Test(); public static void main(String[] args) { int i = -1; System.out.println(i >>>= 10); long l = -1; System.out.println(l >>>= 10); short s = -1; System.out.println(s >>>= 10); byte b = -1; System.out.println(b >>>= 10); b = -1; System.out.println(b>>>10); monitor.expect(new String[] { "4194303", "18014398509481983", "-1", "-1", "4194303" }); } } ///:~ b 3¨g mP OÅ~¬ b àÒ]ª!Q, DEA Ùx( ¶ ]â,Dm1>( (0 //: c03:BitManipulation.java // Using the bitwise operators. import com.bruceeckel.simpletest.*; import java.util.*; public class BitManipulation { static Test monitor = new Test();
public static void main(String[] args)t Random rand new Random ( and. nextInt(i print printBinaryInt ("+1",+1)i int maxpos =2147483647 printBinaryInt ("maxpos", maxpos)i int maxneg =-2147483648 printBinaryInt("maxneg", maxneg)i printBinaryInt("i ,i) printBinaryInt (wi",wi)i printBinary print BinaryInt("3", 3) printBinaryInt("i&j",i&j)i print ) printBinaryInt("i j",i 3) intBinaryInt ("i itBi printBinaryInt("(+1)>> 5 ,(*1)>>5)i printBinaryInt("i >>>5",i>>>5)i printBinaryInt ("(+1)>>>5",(41)>>>5) ong xiLong()i rand. nextLong ()i printBinaryLong("-IL",-1L) printBinaryLong("+1 1ong11=9223372036854775807L printBinaryLong ("maxp long1in=-9223372036854775808L; printBinaryLong("l",1) printBinaryLong(*l",4l) printBinaryLong( 1) printBinaryLong("m",m) printBinaryLong("1& m", l m)i printBinarylong("1 I m",1 I m) printBinaryLong ("1 m", m) printBinaryLong("1<< 5,1<< 5)i printBinaryLong("1 >>5",1>>5) printBinaryLong("(1)>> 5",(+1)>>5)i printBinaryLong("1>>>5",1>>>5)i printBinaryLong("(+1)>>> 5",(+1)>>>5) monitor. expect("BitManipulation out") static void printBinaryInt (String s, int i) i System. out. println( Int System. out. print( for (int 1;j>=0;j--) System. out. print("1") System. out. print ("0") System. out. println ()i static void printBinaryLong(String s, long 1) System. out. println( System. out 0;i--) 第17页共48页
shhgs@wgqqh.com 17 ✁ ✂ 48 ✁ public static void main(String[] args) { Random rand = new Random(); int i = rand.nextInt(); int j = rand.nextInt(); printBinaryInt("-1", -1); printBinaryInt("+1", +1); int maxpos = 2147483647; printBinaryInt("maxpos", maxpos); int maxneg = -2147483648; printBinaryInt("maxneg", maxneg); printBinaryInt("i", i); printBinaryInt("~i", ~i); printBinaryInt("-i", -i); printBinaryInt("j", j); printBinaryInt("i & j", i & j); printBinaryInt("i | j", i | j); printBinaryInt("i ^ j", i ^ j); printBinaryInt("i << 5", i << 5); printBinaryInt("i >> 5", i >> 5); printBinaryInt("(~i) >> 5", (~i) >> 5); printBinaryInt("i >>> 5", i >>> 5); printBinaryInt("(~i) >>> 5", (~i) >>> 5); long l = rand.nextLong(); long m = rand.nextLong(); printBinaryLong("-1L", -1L); printBinaryLong("+1L", +1L); long ll = 9223372036854775807L; printBinaryLong("maxpos", ll); long lln = -9223372036854775808L; printBinaryLong("maxneg", lln); printBinaryLong("l", l); printBinaryLong("~l", ~l); printBinaryLong("-l", -l); printBinaryLong("m", m); printBinaryLong("l & m", l & m); printBinaryLong("l | m", l | m); printBinaryLong("l ^ m", l ^ m); printBinaryLong("l << 5", l << 5); printBinaryLong("l >> 5", l >> 5); printBinaryLong("(~l) >> 5", (~l) >> 5); printBinaryLong("l >>> 5", l >>> 5); printBinaryLong("(~l) >>> 5", (~l) >>> 5); monitor.expect("BitManipulation.out"); } static void printBinaryInt(String s, int i) { System.out.println( s + ", int: " + i + ", binary: "); System.out.print(" "); for(int j = 31; j >= 0; j--) if(((1 << j) & i) != 0) System.out.print("1"); else System.out.print("0"); System.out.println(); } static void printBinaryLong(String s, long l) { System.out.println( s + ", long: " + l + ", binary: "); System.out.print(" "); for(int i = 63; i >= 0; i--)