将16进制字符转换成10进制

## 题目要求 ##
将16进制字符转换成10进制，在字符串不是16进制字符串时抛出NumberFormatException异常。

public class display {
public static void main(String[] args) {
System.out.println(parseHex("A5"));
System.out.println(parseHex("FAA"));
System.out.println(parseHex("A5"));
System.out.println(parseHex("ABC"));
System.out.println(parseHex("J"));
}

public static int parseHex(String hexString) {
int value = convertHexToDec(hexString.charAt(0));
for (int i = 1; i < hexString.length(); i++) {
value = value * 16 + hexString.charAt(i) - '0';
}

return value;
}

static int convertHexToDec(char ch) {
if (ch == 'A') {
return 10;
}
else if (ch == 'B') {
return 11;
}
else if (ch == 'C') {
return 12;
}
else if (ch == 'D') {
return 13;
}
else if (ch == 'E') {
return 14;
}
else if (ch == 'F') {
return 15;
}
else if (ch <= '9' && ch >= '0')
return ch - '0';
else
throw new NumberFormatException("Illegal character: " + ch);
}
}

## 结果 ##