Java - Generating a random number with specified bit length?

I'm trying to make a function that can generate a random number and specify how many bits the random number can be.

More specifically, I am trying to generate a number that could either be 8, 10, or 12 bits long. This bit amount is specified by another variable.

I then want to represent this number as a hex in string or as an signed and unsigned integer in decimal. I think i can just use the various Integer.toString methods for that part.

How would I go about generating specific bit-length random numbers in Java?

So far, I have this function skeleton in place:

public static String generateQuestion(int numBits, int taskType){
    String questionStr = "";
    String questionVal = ""; // This is the string hexadecimal version of the randomly generated number
    // TODO: Code to generate random value based on numBits
    

    switch(taskType){
        case 0: // Hex to Decimal
            questionStr = "What are the signed and unsigned values for the " + numBits + "-bit value " + questionVal + "?";
            return questionStr; // Return the constructed string
        case 1: // Signed Decimal to Hex
        case 2: // Unsigned Decimal to Hex
        default:
            throw new IllegalStateException("Unexpected Question Type: " + taskType); // In case the task type is something other than the 3 possible question types
    }
}