Step 1: Understand the Concept

Understanding the conversion from octal to hexadecimal is the first critical step. Octal is a base-8 number system, whereas hexadecimal is a base-16 system. Direct conversion from octal to hexadecimal isn't straightforward, hence we first need to convert the octal number to a binary number because both octal and hexadecimal are simplified forms of binary.

Step 2: Convert Octal to Binary

To convert an octal number to a binary number, take each digit of the octal number, and replace it with its corresponding 3-digit binary number. Please note that Octal numbers range from 0-7 hence every octal digit can be represented by 3 bits.

Step 3: Convert Binary to Hexadecimal

After obtaining a binary number, the next step is to convert this binary number to a hexadecimal number. For this, we need to group the binary number into 4-bit groups (from right to left), and then replace every binary group with its corresponding hex digit.

Step 4: Implementing the Conversion in Java

In Java, you don't need to do this all manually. You have functions Integer.parseInt(arg1, arg2) and Integer.toHexString(arg3). Integer.parseInt(arg1, arg2) returns the decimal representation of the specified Octal String arg1 (arg2 is the radix of arg1), and Integer.toHexString(arg3) returns the hexadecimal string of the provided decimal number arg3.

public static String convertOctalToHex(String octal){
    int decimal = Integer.parseInt(octal, 8);
    return Integer.toHexString(decimal).toUpperCase();
}

Conclusion

We learned that to convert an octal number to a hexadecimal number, first convert the octal to binary and then the binary to hexadecimal. But in Java, you don't need to worry about these conversions as Java provides built-in methods to do the conversions directly.