移位操作是把数据看作是二进制数，然后将其向左或向右移动若干位的运算。在Java编程语言中，移位操作符包含三种，分别是 <<（左移）、 >>（带符号右移）和 >>>（无符号右移），这三种操作符都只能作用于long、int、short、byte、char这几种基本的整型类型上。
左移操作符 <<
左移操作符 << 是将数据转换成二进制数后，向左移若干位，高位丢弃，低位补零。
private static void leftV1() {
int i = -1;
System.out.println("Before << , i's value is " + i);
System.out.println("i's binary string is " + Integer.toBinaryString(i));
i <<= 10;
System.out.println("After << , i's value is " + i);
System.out.println("i's binary string is " + Integer.toBinaryString(i));
}
输出结果
Before << , i's value is -1
i's binary string is 11111111111111111111111111111111
After << , i's value is -1024
i's binary string is 11111111111111111111110000000000
带符号右移操作符 >>
众所周知，Java中整型表示负数时，最高位为符号位，正数为0，负数为1。>> 是带符号的右移操作符，将数据转换成二进制数后，向右移若干位，高位补符号位，低位丢弃。
private static void rightV1() {
// 对正数进行右移操作
int i1 = 4992;
System.out.println("Before >> , i1's value is " + i1);
System.out.println("i1's binary string is " + Integer.toBinaryString(i1));
i1 >>= 10;
System.out.println("After >> , i1's value is " + i1);
System.out.println("i1's binary string is " + Integer.toBinaryString(i1));
// 对负数进行右移操作
int i2 = -4992;
System.out.println("Before >> , i2's value is " + i2);
System.out.println("i2's binary string is " + Integer.toBinaryString(i2));
i2 >>= 10;
System.out.println("After >> , i2's value is " + i2);
System.out.println("i2's binary string is " + Integer.toBinaryString(i2));
}
输出结果
Before >> , i1's value is 4992
i1's binary string is 1001110000000
After >> , i1's value is 4
i1's binary string is 100
Before >> , i2's value is -4992
i2's binary string is 11111111111111111110110010000000
After >> , i2's value is -5
i2's binary string is 11111111111111111111111111111011
无符号右移操作符 >>>
无符号右移操作符 >>>与>>类似，都是将数据转换为二进制数后右移若干位，不同之处在于，不论负数与否，结果都是高位补零，低位丢弃。
private static void rightV2() {
int i3 = -4992;
System.out.println("Before >>> , i3's value is " + i3);
System.out.println("i3's binary string is " + Integer.toBinaryString(i3));
i3 >>>= 10;
System.out.println("After >>> , i3's value is " + i3);
System.out.println("i3's binary string is " + Integer.toBinaryString(i3));
}
输出结果
Before >>> , i3's value is -4992
i3's binary string is 11111111111111111110110010000000
After >>> , i3's value is 4194299
i3's binary string is 1111111111111111111011
java 基本类型的长度
- byte
-
- 8位，占1个字节
- 最小值为 -2^7
- 最大值为 2^7-1
- short
-
- 16位，占2个字节
- 最小值为 -2^15
- 最大值为 2^15-1
- int
-
- 32位，占4个字节
- 最小值为 -2^31
- 最大值为 2^31-1
- long
-
- 64位，占8个字节
- 最小值为 -2^63
- 最大值为 2^63-1
- float
-
- 32位，占4个字节
- double
-
- 64位，占8个字节
- char
-
- 16位，占2个字节
注意
Java在处理byte、short、char的移位操作前，会先将其转型成int类型，然后再进行操作
private static void byteTest() {
byte b = -1;
System.out.println("Before >> , b's value is " + b);
System.out.println("b's binary string is " + Integer.toBinaryString(b));
System.out.println("After >> , b's value is " + (b >>> 6));
System.out.println("b's binary string is " + Integer.toBinaryString(b >>> 6));
}
输出结果
Before >> , b's value is -1
b's binary string is 11111111111111111111111111111111
After >> , b's value is 67108863
b's binary string is 11111111111111111111111111
如果移位超过数值所占的位数，对于int类型，只取其低5位，也就是取rhs % 32的结果；对于long类型，只取其低6位，也即是取rhs % 64的结果
private static void beyondTest() {
int i4 = -1;
System.out.println("Before >>> , i4's value is " + i4);
System.out.println("i4's binary string is " + Integer.toBinaryString(i4));
System.out.println("After >>> 31 , i4's value is " + (i4 >>> 31));
System.out.println("i4's binary string is " + Integer.toBinaryString(i4 >>> 31));
System.out.println("After >>> 32 , i4's value is " + (i4 >>> 32));
System.out.println("i4's binary string is " + Integer.toBinaryString(i4 >>> 32));
System.out.println("After >>> 33 , i4's value is " + (i4 >>> 33));
System.out.println("i4's binary string is " + Integer.toBinaryString(i4 >>> 33));
}
输出结果
Before >>> , i4's value is -1
i4's binary string is 11111111111111111111111111111111
After >>> 31 , i4's value is 1
i4's binary string is 1
After >>> 32 , i4's value is -1
i4's binary string is 11111111111111111111111111111111
After >>> 33 , i4's value is 2147483647
i4's binary string is 1111111111111111111111111111111
