java 位操作 bitwise(按位) operation bit

java 位操作 bitwise(按位) operation bit

//一篇对于 原码 反码 补码 的介绍

 http://www.cnblogs.com/zhangziqiu/archive/2011/03/30/ComputerCode.html

 

java中有三种移位运算符

<<      :     左移运算符，num << 1,相当于num乘以2

>>      :     右移运算符，num >> 1,相当于num除以2

>>>    :     无符号右移，忽略符号位，空位都以0补齐

 

// 8   0000 0000 0000 1000     原码
    　 1111 1111 1111 0111     反码

+　　　　　　　　　　　　  1

　　　1111 1111 1111 1000     （8的补码）来表示 -8

 

// -8 1111 1111 1111 1000 65528     补码（正值 的反码+1）

// 65535 1111 1111 1111 1111 65535
// 65535-65528=7+1=8

 

操作longValue = longValue | (1 << n); 可以在longValue的2进制表示中，把从右边数到左边数第n + 1位的值设置为1，并且不影响其他位上面的值   即用0和2进制值变量x做或|or操作，不会影响到2进制变量x的值 

操作longValue = longValue & ~(1 << n); 可以在longValue的2进制表示中，把从右边数到左边数第n + 1位设置为0，并且不影响其他位上面的值   即用1和2进制值变量x做与&and操作，不会影响到2进制变量x的值 

操作System.out.println((longValue >> n & 1) == 1); 可以判断值longValue的2进制表示中，从右边数到左边第n + 1位的值是0false 还是1true 

public class bitOperation {

    /**
     * @param args
     */
    public static void main(String[] args) {

        long longValue = 0;

        longValue = longValue | (1 << 0);
        // 1
        System.out.println(Long.toBinaryString(longValue));
        longValue = longValue | (1 << 1);
        // 11
        System.out.println(Long.toBinaryString(longValue));
        longValue = longValue | (1 << 4);
        // 10011
        System.out.println(Long.toBinaryString(longValue));
        longValue = longValue | (1 << 5);
        // 110011
        System.out.println(Long.toBinaryString(longValue));
        longValue = longValue | (1 << 6);
        // 1110011
        System.out.println(Long.toBinaryString(longValue));

        String hex = Long.toBinaryString(longValue);
        // 1110011
        System.out.println(hex);
        // 115
        System.out.println(Integer.valueOf("1110011", 2));
        // 1110011
        System.out.println(Long.toBinaryString(longValue >> 0));
        // 1
        System.out.println(Long.toBinaryString(longValue >> 0 & 1));
        // 111001
        System.out.println(Long.toBinaryString(longValue >> 1));
        // 1
        System.out.println(Long.toBinaryString(longValue >> 1 & 1));
        // true
        System.out.println((longValue >> 0 & 1) == 1);
        // true
        System.out.println((longValue >> 1 & 1) == 1);
        // false
        System.out.println((longValue >> 2 & 1) == 1);
        // false
        System.out.println((longValue >> 3 & 1) == 1);
        // true
        System.out.println((longValue >> 4 & 1) == 1);
        // true
        System.out.println((longValue >> 5 & 1) == 1);
        // true
        System.out.println((longValue >> 6 & 1) == 1);
        // false
        System.out.println((longValue >> 7 & 1) == 1);

        // Demonstrate the bitwise logical operators.
        bitLogic();
        // Left shifting a byte value.
        byteShift();
    }

    /**
     * Left shifting a byte value.
     */
    private static void byteShift() {
        byte a = 64, b;
        int i;

        i = a << 2;
        b = (byte) (a << 2);

        // Original value of a: 64
        System.out.println("Original value of a: " + a);
        // i and b: 256 0
        System.out.println("i and b: " + i + " " + b);
        System.out.println("\r\n");
    }

    /**
     * Demonstrate the bitwise logical operators.
     */
    private static void bitLogic() {
        String binary[] = { "0000", "0001", "0010", "0011", "0100", "0101",
                "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101",
                "1110", "1111"

        };
        int a = 3; // 0 + 2 + 1 or 0011 in binary
        int b = 6; // 4 + 2 + 0 or 0110 in binary
        int c = a | b;
        int d = a & b;
        int e = a ^ b;
        int f = (~a & b) | (a & ~b);
        int g = ~a & 0x0f;

        // a = 0011 = 3
        System.out.println(" a = " + binary[a] + " = " + a);
        // b = 0110 = 6
        System.out.println(" b = " + binary[b] + " = " + b);
        // a|b = 0111 = 7
        System.out.println(" a|b = " + binary[c] + " = " + c);
        // a&b = 0010 = 2
        System.out.println(" a&b = " + binary[d] + " = " + d);
        // a^b = 0101 = 5
        System.out.println(" a^b = " + binary[e] + " = " + e);
        // ~a&b|a&~b = 0101 = 5
        System.out.println("~a&b|a&~b = " + binary[f] + " = " + f);
        // ~a = 1100 = 12
        System.out.println(" ~a = " + binary[g] + " = " + g);
        System.out.println("\r\n");
    }
}