java 位移、异或运算笔记

异或1

奇偶数:十进制转二进制数逐个位数异或的值为零是奇数

private static void isOdd(int a) {
        int b = 0;
        String binStr = Integer.toBinaryString(a);

        for (int x = 0, len = binStr.length() - 1; x < len; x++) {
            b = b ^ (binStr.charAt(x) ^ binStr.charAt(x + 1));
        }
        System.out.println(a + " > 二进制: " + binStr);
        System.out.println(a + "=" + (b == 0 ? "奇数" : "偶数"));
}

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isOdd(10)

 

 

 

 

 

异或2

两整数交换

int a = 10, b = 9;
a ^= b;
b ^= a;
a ^= b;
System.out.println("a:" + a + ", b:" + b);

 

 

 

 

 

异或3

任意一个数异或零都为它本身

int c = 100;
c ^= 0;
System.out.println("c:" + c);

 

 

 

位移运算

左位移 = 乘以2的n次幂,右位移 = 除以2的n次幂:

8 << 3(n) = 64, 8 >> 3(n) = 1

System.out.println("===>> " + (8*(2 * 2 * 2)) + ", " + (8 << 3));
System.out.println("===>> " + (8 / (2 * 2 * 2)) + ", " + (8 >> 3));

 

 

 

与运算

取模,n-1相与：9 % 4(n) = 9 & (4 - 1) = 1

System.out.println((9 % 4) + ", " + (9 & 3));

 

 附:为什么HashMap的容量总是2的n幂次方