基础练习 十六进制转八进制

import java.util.HashMap;
import java.util.Scanner;

public class Main {
    static String[] Binary = {"0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111"};
    static String[] Octal = {"000","001","010","011","100","101","110","111"};
    static HashMap<String, String> map;
    /*
     * Binary是0-15的二进制数的数组
     * Octal是0-7的二进制数的水族
     * map是0-7与其二进制数的映射
     */

    //16进制转2进制方法
    public static String HexToBinary(String hex){
        StringBuffer binary = new StringBuffer();
        for ( int i = 0 ; i < hex.length() ; i++){
            char ch = hex.charAt(i);
            if ( ch >= '0' && ch <= '9' ){
                binary.append(Binary[(int)(ch-'0')]);
            }else{
                binary.append(Binary[(int)(ch-'A')+10]);
            }
        }
        return binary.toString();
    }

    //2进制转8进制方法
    public static String BinaryToOctal(String binary){
        StringBuffer octal = new StringBuffer();
        int reminder = binary.length() % 3;
        //sub为2进制数需要补充0的个数
        int sub = 0;
        if ( reminder != 0)
            sub = 3 - reminder;
        StringBuffer tmp = new StringBuffer();
        for ( int i = 0 ; i < sub ; i++){
            tmp.append("0");
        }
        tmp.append(binary);
        for ( int i = 0 ; i <= tmp.length() - 3 ; i += 3){
            String substring = tmp.substring(i, i+3);
            octal.append(map.get(substring));
        }
        int index = FindZero(octal);
        /*
         * 如果index为-1，则8进制数前面没有0，
         * 反之则有0，取无0的子字符串。
         */
        if(index == -1)
            return octal.toString();
        else
            return octal.substring(index+1).toString();
    }

    //统计8进制数的字符串的最前面连续0的个数，返回的最后一个0的下标
    public static int FindZero(StringBuffer octal){
        int index = -1;
        for ( int i = 0 ; i < octal.length() ; i++){
            if ( octal.charAt(i) == '0'){
                index = i;
                continue;
            }else{      
                break;
            }
        }
        return index;
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner in = new Scanner(System.in);
        map = new HashMap<String, String>();
        for ( int i = 0 ; i < Octal.length ; i++){
            char[] ch = new char[1];
            ch[0] = (char) (i+'0');
            String str = new String(ch);
            map.put(Octal[i], str);
        }
        int num = in.nextInt();
        for (int i = 0 ; i < num ; i++){
            String hex = in.next();
            String binary = HexToBinary(hex);
            String octal = BinaryToOctal(binary);
            System.out.println(octal);
        }
        in.close();
    }

}