Java 子网划分器：高效计算子网掩码、IP 范围，支持超网功能

package 子网划分器;

import java.io.*;

public class SubnetCalculator {

public static void main(String[] args) throws IOException {
    String ip; //用于接收要划分的IP
    int s; //用于接收要划分的子网数
    int n; //输入子网数对应的二进制位数

    System.out.println("---------------划分子网---------------");

    //输入要划分的IP地址:ip
    System.out.println("请输入要划分的IP地址(格式为：x1.x2.x3.x4)：");
    System.out.print("→:");
    InputStreamReader isr = new InputStreamReader(System.in);
    BufferedReader br = new BufferedReader(isr);
    ip = br.readLine();

    //截取x1
    int index1 = ip.indexOf('.');
    String st1 = ip.substring(0, index1);
    int x1 = Integer.parseInt(st1);

    //截取x2
    int index2 = ip.indexOf('.', index1 + 1);
    String st2 = ip.substring(index1 + 1, index2);
    int x2 = Integer.parseInt(st2);

    //截取x3
    int index3 = ip.indexOf('.', index2 + 1);
    String st3 = ip.substring(index2 + 1, index3);
    int x3 = Integer.parseInt(st3);

    //截取x4
    int x4 = Integer.parseInt(ip.substring(index3 + 1));

    //判断IP地址类型并输出可划分的最大子网数
    int maxSubnets = 0;
    if (x1 >= 1 && x1 <= 126) { //A类
        maxSubnets = (int) Math.pow(2, 24 - 2) - 2;
    } else if (x1 >= 128 && x1 <= 191) { //B类
        maxSubnets = (int) Math.pow(2, 16 - 2) - 2;
    } else if (x1 >= 192 && x1 <= 223) { //C类
        maxSubnets = (int) Math.pow(2, 8 - 2) - 2;
    }
    System.out.println("本IP地址能划分的最大子网数为: " + maxSubnets);

    //输入要划分的子网数:s
    System.out.println("请输入要划分的子网数：");
    System.out.print("→:");
    String subnet_num = br.readLine();
    s = Integer.parseInt(subnet_num);
    br.close();

    //求所输入子网数对应的二进制位数:n
    for (n = 1; (Math.pow(2, n) - 2) < s; n++) ;
    System.out.println("--------------------------------------");

    //求子网掩码
    int sum = 0;
    for (int i = 0; i < n; i++) {
        sum = sum + (int) Math.pow(2, (7 - i));
    }
    System.out.println("子网掩码为：" + maskToString(sum));

    //求每个子网段的主机数
    int maxHosts = 0;
    if (x1 >= 1 && x1 <= 126) { //A类
        maxHosts = (int) Math.pow(2, (32 - n)) - 2;
    } else if (x1 >= 128 && x1 <= 191) { //B类
        maxHosts = (int) Math.pow(2, (16 - n)) - 2;
    } else if (x1 >= 192 && x1 <= 223) { //C类
        maxHosts = (int) Math.pow(2, (8 - n)) - 2;
    }
    System.out.println("每个子网段的主机数：" + maxHosts);

    //输出各子网IP范围
    System.out.println("各子网IP范围如下：");
    int subnet_id = 0;
    int[] subnetAddress = {x1, x2, x3, 0}; //子网地址，最后一个元素先占位，后面再根据需要填充
    int[] broadcastAddress = {x1, x2, x3, 0}; //广播地址，最后一个元素先占位，后面再根据需要填充
    for (int i = 1; i <= s; i++) {
        subnet_id++;
        int sub_id = (int) Math.pow(2, (8 - n)) * (i - 1);
        subnetAddress[3] = sub_id;
        broadcastAddress[3] = sub_id + (int) Math.pow(2, (8 - n)) - 1;
        System.out.print("<" + subnet_id + ">" + " ");
        System.out.println(addressToString(subnetAddress) + " --- " + addressToString(broadcastAddress));
    }
    System.out.println("子网划分完毕");
}

//将32位子网掩码转换为点分十进制字符串
private static String maskToString(int mask) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < 4; i++) {
        int num = 0;
        for (int j = 0; j < 8; j++) {
            num += ((mask & 1) << (7 - j));
            mask >>= 1;
        }
        sb.append(num);
        if (i < 3) {
            sb.append(".");
        }
    }
    return sb.toString();
}

//将IP地址数组转换为点分十进制字符串
private static String addressToString(int[] address) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < 4; i++) {
        sb.append(address[i]);
        if (i < 3) {
            sb.append(".");
        }
    }
    return sb.toString();
}

}