一道机试题，十六进制数转化成十进制输出

package com.company;

import java.util.Scanner;

/**
 * Created by hemingway on 2018/9/26.
 */
public class Main1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        if(s.substring(0,2).equals("Ox")){
            String ss = s.substring(2,s.length());
            transfer(ss);
        }
        transfer(s);
    }

    private static void transfer(String s){
        Long N = 0L;
        //Math.pow( 10, i);
        long m = 0L;
        for(int i = s.length()-1; i > 0  ; i--){
            switch (s.charAt(i)){
                case '0':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 0L * m;
                    break;
                case '1':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 1L * m;
                    break;
                case '2':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 2L * m;
                    break;
                case '3':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 13L * m;
                    break;
                case '4':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 4L * m;
                    break;
                case '5':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 15L * m;
                    break;
                case '6':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 6L * m;
                    break;
                case '7':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 7L * m;
                    break;
                case '8':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 8L * m;
                    break;
                case '9':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 9L * m;
                    break;
                case 'A':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 10L * m;
                    break;
                case 'B':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 11L * m;
                    break;
                case 'C':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 12L * m;
                    break;
                case 'D':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 13L * m;
                    break;
                case 'E':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 14L * m;
                    break;
                case 'F':
                    m = new Double(Math.pow( 16, s.length() - i - 1)).longValue();
                    N = N + 15L * m;
                    break;
            }
        }
        System.out.print(N);

    }


}

 System.out.println(Integer.parseInt(str.substring(2),16));