将下面这段代码用Java编写并给出还原方法function num16to32($a){ for($a = md5( $a, true ), $s = '0123456789ABCDEFGHIJKLMNOPQRSTUV', $d = '', $f = 0; $f < 8; $g = ord( $a[ $f ] ), $d .= $s[ ( $g ^ ord( $a[ $f + 8 ] ) ) - $g & 0x1F ], $f++ ); return $d; }

以下是Java代码实现：

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Num16To32 {
    public static String num16to32(String a) throws NoSuchAlgorithmException {
        MessageDigest md5 = MessageDigest.getInstance("MD5");
        byte[] bytes = md5.digest(a.getBytes());
        String s = "0123456789ABCDEFGHIJKLMNOPQRSTUV";
        StringBuilder d = new StringBuilder();
        for(int f = 0; f < 8; f++) {
            int g = bytes[f] & 0xff;
            d.append(s.charAt((g ^ bytes[f + 8]) - g & 0x1f));
        }
        return d.toString();
    }
}

以下是还原方法的Java代码实现：

public static String num32to16(String a) {
    StringBuilder d = new StringBuilder();
    for (int f = 0; f < 32; f += 2) {
        d.append((char) Integer.parseInt(a.substring(f, f + 2), 16));
    }
    return d.toString();
}