将一个运算对象的各二进制位全部左移若干位（左边的二进制位丢弃，右边补0）。
例：a = a << 2 将a的二进制位左移2位，右补0，
左移1位后a = a *2;
若左移时舍弃的高位不包含1，则每左移一位，相当于该数乘以2。
public class MainClass {
public static void main(String[] args) {
long i = 1L << 3;
System.out.println(Long.toBinaryString(i));
i = 1L << 63;
System.out.println(Long.toBinaryString(i));
i = 1L << 64;
System.out.println(Long.toBinaryString(i));
}
}
下面是输出的结果：1000<pre name="code" class="java">1000000000000000000000000000000000000000000000000000000000000001
i = 3L << 63
If the promoted type of the left-hand operand is int, only the five lowest-order bits of the right-hand operand are used as the shift distance. It is as if the right-hand operand were subjected to a bitwise logical AND operator & (§15.22.1) with the mask value 0x1f (0b11111). The shift distance actually used is therefore always in the range 0 to 31, inclusive. If the promoted type of the left-hand operand is long, then only the six lowest-order bits of the right-hand operand are used as the shift distance. It is as if the right-hand operand were subjected to a bitwise logical AND operator & (§15.22.1) with the mask value 0x3f (0b111111). The shift distance actually used is therefore always in the range 0 to 63, inclusive.
public class SF{
public static void main(String[] args) {
new SF().sh(1,2);
}
public int sh(int a , int b){
return (a << 32);
}
}javac SF.java javap -verbose SF > sfp.txt java -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -Xcomp -XX:CompileCommand=dontinline,*SF.sh -XX:CompileCommand=compileonly,*SF.sh SF > sfasm.txt pause
[Verified Entry Point]
0x01c92e50: mov %eax,-0x4000(%esp)
0x01c92e57: push %ebp
0x01c92e58: sub $0x18,%esp ;*iload_1
; - SF::sh@0 (line 7)
0x01c92e5b: shl $0x0,%edx
0x01c92e5e: mov %edx,%eax
0x01c92e60: add $0x18,%esp
0x01c92e63: pop %ebp
0x01c92e64: test %eax,0x140100 ; {poll_return}Java移位运算符 “<<” 作用及详解,布布扣,bubuko.com
原文地址：http://blog.csdn.net/zjx409/article/details/37569055
