如何在Java中交换两位整数?

Question

是否有一个内置的函数在Java中，我可以用它来交换两个比特?

例如:

_ _ _ _ 1 _ _ 0 bit 3与bit 0交换成为_ _ _ _ 0 _ _ 1

我知道这可以用一个很长的按位操作过程来完成，但我想避免这样做。

Answer 1

你也可以这样做

//positions are indexed from 0 and in order ...[4][3][2][1][0]
//so changing 3 and 0 will make             ...[4][0][2][1][3]
public static int swapBits(int n, int pos1, int pos2) {
    int bit1 = (n >> pos1) & 1;// bit at pos1
    int bit2 = (n >> pos2) & 1;// bit at pos2
    if (bit1 == bit2) // no need to swap since we change 1 with 1 or 0 with 0
        return n;     // so we can return original value
    // Since we are here it means that we need to change 1->0 and 0->1.
    // To do this we can use XOR (^).
    // Lets create mask like 000001001 with 1 at positions which need "reversing"
    int mask = (1 << pos1) | (1 << pos2);
    
    return n ^ mask;// TA-DAH!!!
}

Answer 2

还有另一种方法，叫做delta-swap。

int t = (i ^ (i >> 3)) & 1;
return i ^ t ^ (t << 3);

或者更一般的:

static int swap(int x, int i, int j)
{
    // precondition: i > j
    int d = i - j;
    int y = (x ^ (x >> d)) & (1 << j);
    return x ^ y ^ (y << d);
}

Answer 3

我正在详细制作，但您可以将其合并为一行

 int temp1 = (i & 0x1) << 3; //extract lowest bit #1 and place at pos# 4
 int temp2 = (i & 0x8) >> 3; //extract bit #4 and place at pos #1
 i = (i & temp1) | (i & ~temp1); //now pos #4 is ready     
 i = (i & temp2) | (i & ~temp2); //now pos #1 is ready