java位运算笔记

位运算：

~（非）——》二进制数进行0和1的互换

样例：

public class Test {
  public static void main(String[] args) {
    System.out.println(~-2);//输出1
    System.out.println(~-1);//输出0
    System.out.println(~0);//输出-1
    System.out.println(~1);//输出-2
    System.out.println(~2);//输出-3
    System.out.println(~3);//输出-4
  }
}

^（异或）——》12 ^ 10 = ...01100^01010 =  00110 = 6

样例：

public class Test {
  public static void main(String[] args) {
    int a = 0;
    int b = 0;
    b = a = 12^10;
    System.out.println(a);//输出为 6
    a = a^12;
    System.out.println(a);//输出为 10
    b = b^10;
    System.out.println(b);//输出为 12
  }
}

应用：二个不同的数进行交换

public class Test {
  public static void main(String[] args) {
    int a = 12;
    int b = 10;
    System.out.println(a + "---" + b);// 输出为12---10
    a = a ^ b;
    b = a ^ b;
    a = a ^ b;
    System.out.println(a + "---" + b);// 输出为10---12
  }
}

&（与）——》12 & 10 = ...01100 & 01010 = 01000 = 8

样例：

public class Test {
  public static void main(String[] args) {
    int a = 12;
    int b = 10;
    int c = a&b;
    System.out.println(c);//输出为 8
  }
}

应用：

public class Test {
  public static void main(String[] args) {
    int[] a = new int[2];
    a[0] = 5;
    a[1] = 6;
    for (int i = 0; i < a.length; i++) {
      if ((a[i] & 1) == 1) {// 推断是否为奇数
        System.out.println(a[i] + "奇数");
      } else {
        System.out.println(a[i] + "偶数");
      }
    }
    // 输出为：
    // 5"奇数"
    // 6"偶数"
  }
}

|（或）——》12 | 10 = ...01100 | ...01010 = 01110 = 14

样例：

public class Test {
  public static void main(String[] args) {
    int a = 12;
    int b = 10;
    // ...01100 | ...01010 = 01110 = 14
    int c = a | b;
    System.out.println(c);// 输出为14
  }
}

应用：和位移一起运算能够打包成不同位数的整数

public class Test {
  public static void main(String[] args) {
    int a = 1;
    int b = 2;
    // 256 | 2 = ...01 0000 0000 | ...0010 = ...01 0000 0010 = 258
    int c = a << 8 | b;
    System.out.println(c);// 输出为258
  }
}

>>（右位移）——》12>>2 = 00...01100 >>2 = 00...00011 = 3

-1 >>>24 = 1111...111 >>>24 = 1111...1111 1111 = -1

>>>（无符号）——》 -1 >>> 24 = 1111...111 >>> 24 = 0000...1111 1111 = 255

public class Test {
  public static void main(String[] args) {
    int a = -1;
    // 1111...111 >>> 24 = 0000...1111 1111 = 255
    int b = a>>>24;
    System.out.println(b);// 输出为255
  }
}

12>>2 = 00...01100 >>2 = 00...00011 = 3