Java – bitwise OP unexpectedly becomes negative

Can someone explain to me why I got these results?

public static int ipv4ToInt(String address) {
    int result = 0;

    // iterate over each octet
    for(String part : address.split(Pattern.quote("."))) {

        // shift the prevIoUsly parsed bits over by 1 byte
        result = result << 8;

        System.out.printf("shift = %d\n",result);

        // set the low order bits to the current octet
        result |= Integer.parseInt(part);

        System.out.printf("result = %d\n",result);
    }
    return result;
}

For IPv4 toint ("10.35.41.134"), I get:

This is the same as the result I got when I did my own mathematical calculation

For IPv4 toint ("192.168.0.1"), I get:

For this, when I do the math manually, I get 3232235521

Interestingly: 3232235521 = 11000000010101000000000000000000 1 when I enter 1062731775 to enter my windows Calc and press the / – button, I get: - 1062731775 = 11111111111111111111111111111 110000000101010000000000000000 1

This function still works for my purpose, but I'm really curious. Why does the earth result become negative when I make the last conversion?

Solution

Because your situation overflows!

In Java, integers are also 32 bits, ranging from - 2147483648 to 2647

12625920 < < 8 crosses the limit of 2 ^ 31-1, so the result becomes negative The result is just a flip from the - ve side, so any range left from the positive is accompanied by so much from the negative! As suggested, you should use the long variable to avoid overflow!