用一個 int 表示 IP地址

用一個 int 表示 IP地址。這還是08年初，面試華爲時被問到的，當時也回答上來了。不過，最終 HR 也沒要我就是了 :)

public class IP2Integer {

	/**
	 * Convert an integer to a IPV4
	 * 
	 * <code>iIPV4</code>'s highest byte represents the first ip seg
	 * 
	 * @param iIPV4
	 * @return
	 */
	public static String integer2IPV4(int iIPV4) {
		StringBuilder sb = new StringBuilder();
		for (int i = 3; i >= 0; i--) {
			// right shift each byte of iIPV4 to the rightest side
			// and then use 0xFF to mask this new-gotten integer.
			// So we get the integer value of the rightest byte
			int aSeg = (iIPV4 >> (8 * i)) & 0xFF;
			if (i == 0) {
				sb.append(aSeg);
			} else {
				sb.append(aSeg + ".");
			}
		}
		System.out.println(iIPV4 + "-->" + sb.toString());
		return sb.toString();
	}

	/**
	 * Convert a String IPV4 to an integer
	 * 
	 * <code>strIPV4</code>'s first seg is the highest byte of the returned
	 * integer
	 * 
	 * @param strIPV4
	 * @return
	 */
	public static int IPV42Integer(String strIPV4) {
		int iIPV4 = 0x00;
		String[] segArray = strIPV4.split("\\.");
		for (int i = 0; i < segArray.length; i++) {
			// seg <=255, so all the bits except rightest 8 ones are 0
			int seg = Integer.parseInt(segArray[i]);
			// left shift the current iIPV4 1-byte-distance, then "append" the
			// strIPV4Seg to rightest side
			iIPV4 = (iIPV4 << 8) | seg;
		}
		System.out.println(strIPV4 + "-->" + iIPV4);
		return iIPV4;
	}

	public static void main(String[] args) {
		integer2IPV4(IPV42Integer("0.0.0.0"));
		integer2IPV4(IPV42Integer("255.255.255.255"));
		integer2IPV4(IPV42Integer("127.0.0.1"));
		integer2IPV4(IPV42Integer("192.168.1.1"));
		integer2IPV4(IPV42Integer("192.168.0.100"));
		integer2IPV4(IPV42Integer("255.168.0.100"));
	}
}