如何将十六进制转换为以下程序的字节？

public static String asHex (byte buf[]) {
    StringBuffer strbuf = new StringBuffer(buf.length * 2);
    int i;

    for (i = 0; i < buf.length; i++) {
        if (((int) buf[i] & 0xff) < 0x10)
            strbuf.append("0");

        strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
    }

    return strbuf.toString();
}
public static String asHex (byte buf[]) {
    S