16进制转化为10进制

输入：0xA
输出：10

public  static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        String hex = scanner.next();
        if( hex == null || hex.equals("") || !hex.substring(0,2).equalsIgnoreCase("0x")){
            return;
        }


        Map<String,Integer> map = new LinkedHashMap<>();
        char ch = 'A';
        int n = 10;
        while(n<16){
            map.put(ch+"",n);
            ch++;
            n++;
        }

        long sum = 0L;
        String num = hex.substring(2, hex.length());
        String gol = new String();
        for(int j=num.length()-1; 0<=j; j--){
            char temp = num.charAt(j);
            gol += temp;

        }
        for(int i=0; i<gol.length(); i++){
            String k = gol.charAt(i)+"";
            if (map.containsKey(k)) {
                Integer val = map.get(k);
                sum += val*Math.pow(16,i);
                continue;
            }

            try{
                long l = Long.parseLong(k);
                sum += l*Math.pow(16,i);
            }catch (Exception e){
                System.out.println("输入有误");
            }

        }

        System.out.println(sum);
    }

还有直接用parse*方法更加简单：

public class SixteenToTen {
    private  Scanner scanner = new Scanner(System.in);

    private String testStr;

    @Before
    public void initStr(){
        testStr = "0xA1A";
    }
    @Test
    public void scanner(){
        if(testStr == null || testStr.equals("") || !testStr.substring(0,2).equalsIgnoreCase("0x")){
            return ;
        }

        String num = testStr.substring(2);

        int numInt = Integer.parseInt(num, 16);
        System.out.println(numInt);

    }
}