Implement a Java method named parseHex() that converts a String (consisting of digits and uppercase letters ONLY; for now, dont worry about lowercase letters or other characters) from hexadecimal (base 16) to decimal (base 10) and returns the result as an integer. Define a custom HexFormatException class that extends Exception. Your method should throw a HexFormatException if the string is NOT a valid hexadecimal value (e.g., if it contains any uppercase letters outside the range AF).

As a reminder, one basic (pseudocode) algorithm for translating from base N to base 10 is as follows:

total 0 currentPower 1

for each digit/position in the base N value, working from right to left: total total + (current digits value * currentPower) currentPower currentPower * N