subnet-mask.java

import java.lang.String;
public class subnet_mask{
    /*Function to separate the IP entered into 4 different octets*/
    public int[] get_ip_octets(String string) {
        int length = string.length();
        /*This array has 4 rows, one for each octet of the IP address,
   	    and 3 columns, one for each digit of the octet.*/
        int oct[][] = new int[4][3];
        for(int j = 0; j < 4; ++j) {
            for (int q = 0; q < 3; ++q) {
                oct[j][q] = -1;
            }
        }
        String ipnum = string;
        int k = 0;
        int oct_num = 0;
        int oct_digit = 0;
        /*This loop separates the 4 octets of an IP address into the multidimensional array and
   	        converts the values from Chars to Int*/
        while (k < length){
            if(ipnum.charAt(k) != '.'){
                oct[oct_num][oct_digit] = ipnum.charAt(k)- '0';
                oct_digit++;
                k++;
            }
            else {
                k++;
                oct_num++;
                oct_digit = 0;
            }
        }

        int octets[] = {0, 0, 0, 0};
        for(int j = 0; j < 4; j++ ){/*This loop adds the digits*/
            if ( oct[j][2] != -1){
                octets[j] = oct[j][2];
                octets[j] += (oct[j][1] * 10);
                octets[j] += (oct[j][0] * 100);
            }
            else if ( oct[j][2] == -1 && oct[j][1] != -1 ){
                octets[j] += oct[j][1] ;
                octets[j] += oct[j][0] * 10;
            }
            else if ( oct[j][2] == -1 && oct[j][1] == -1 ){
                octets[j] = oct[j][0];
            }
        }
        return octets;
    }
    
    public int [] default_mask(int ip[]){
        int def_mask[] = {0, 0, 0, 0};
        if ( ip[0] > 224 )
            System.exit(0);
        if ( ip[0] > 191 )
            def_mask[2] = 255;
        if ( ip[0] > 127 )
            def_mask[1] = 255;
        if ( ip[0] > 0 )
            def_mask[0] = 255;

        return def_mask;
    }

    public static void main(String[] args) {
        int oct[], def_subnet[];
        subnet_mask sm = new subnet_mask();
        oct = sm.get_ip_octets(args[0]);
        def_subnet = sm.default_mask(oct);
        System.out.print("Network address: ");
        for (int i = 0; i < 4; ++i){
            if( i != 3){
                System.out.printf("%d.", oct[i]);
            }
            else {
                System.out.printf("%d\n", oct[i]);
            }
        }
        System.out.println();
        System.out.print("Default Subnet Mask: ");
        for (int i = 0; i < 4; ++i){
            if( i != 3){
                System.out.printf("%d.", def_subnet[i]);
            }
            else {
                System.out.printf("%d\n", def_subnet[i]);
            }
        }
    }
}