Screenshots of the code with an explanation:
https://media.cheggcdn.com/media/139/139f7b3d-05bb-487c-a40f-5247a50bcdd3/phpZdy2mZ.png

https://media.cheggcdn.com/media/dfe/dfeaec47-0b36-4831-b89f-affb39b81a52/phpEcp1UE.png

https://media.cheggcdn.com/media/864/864eb7d9-7a78-4ccc-9d59-7d8b6b028e58/phpEuHqlI.png

https://media.cheggcdn.com/media/6d6/6d60ed69-de94-4d70-ad1b-b5dd741e6abf/phpsxJ84e.png

https://media.cheggcdn.com/media/69e/69ea753c-2353-4fe3-be6b-2551697667b1/phpijylbP.png

I have Created an extra class to Test our code it's called RamdomGuessGameTest.java it's screenshot:

https://media.cheggcdn.com/media/353/353f145b-531d-4d67-9b7d-6ff7571cbf9c/phptEjUtA.png

The Output Obtained by using the RamdomGuessGameTest.java :

https://media.cheggcdn.com/media/866/866ac81c-ccad-4957-9f82-adb464dcc507/php6x0sPA.png

The Code Used in RandGuessGame.java:


/**
 * Class for a simple, randomized guessing game. Five integer values between 1 and MAX_VALUE (inclusive) will be
 * generated. Only the first and last will be shown to the player. The player must then guess if the sum
 * of all of the numbers is greater than the possible average or not.
 *
 */
public class RandGuessGame
{

    //Declare data members
    public static final int ARR_SIZE = 5;  //Initializing the ARR_SIZE to 5.
    private int arraySum;
    private char guess;
    private int guessTarget;
    private boolean hideMiddleVals;
    private static final int MAX_VALUE = 100;  //Initializing the MAX_VALUE to 100.
    private int[] numbers;
    private java.util.Random rand;

    //Create Constructor
    /**
     * Constructor for the RandGuessGame. Creates "numbers" array of size ARR_SIZE to store random values, sets
     * arraySum to zero, and calculates value of "guessTarget" by multiplying the amount of numbers by half of "MAX_VALUE".
     * The passed Random object is assigned to the class' Random member. hideMiddleVals is defaulted to "true".
     *
     * @param randIn - The random number generator to be used for this instance of the game.
     */
    public RandGuessGame(java.util.Random randIn)  //Initializing the member variable to default values as directed.
    {
        this.numbers = new int[ARR_SIZE]; //creating an array of integer of ARR_SIZE
        this.arraySum = 0;
        this.guessTarget = ARR_SIZE*(MAX_VALUE/2);
        this.rand = randIn;
        this.hideMiddleVals = true;
    }

    //Write member methods

    /**
     * Populates the "numbers" array with random numbers between 1 and "MAX_VALUE".
     */
    public void populateArray()
    {
        for(int i=0;i<ARR_SIZE;i++) //Populating the array of integer with random values.
        {
            this.numbers[i] = rand.nextInt(MAX_VALUE+1); //we have done MAX_VALUE+1 cause we have to include MAX_VALUE also.
        }
    }

    /**
     * Toggles the value of hideMiddleVals. If it is currently true, sets it to false, and vice-versa.
     */
    public void toggleHidden() //We are changing hideMiddlVals to true if it's false and to false if it's true.
    {
        if(this.hideMiddleVals){
            this.hideMiddleVals = false;
        }else{
            this.hideMiddleVals = true;
        }
    }

    /**
     * Returns a String containing the values in the "numbers" array on a single line, separated by spaces with the
     * middle values hidden or all visible based on value of "hideMiddleValue" data member. There is a trailing space
     * on the end, so an example String returned may be: "5 X X X 67 ". NOTE: This does not output to System.out,
     * it generates and returns a String.
     *
     * @overrides toString in class java.lang.Object
     * @return A String with the values of the numbers array. Middle values are hidden if hideMiddleValue is true.
     */
    public java.lang.String toString() //converting the array to string from.
    {
        String output = ""+this.numbers[0]+" "; //first element.
        if(this.hideMiddleVals) //if hideMiddleVals is true we will make all the elements accept the first and last to X.
        {
            for(int i=1;i<ARR_SIZE-1;i++)
            {
                output+=("X ");
            }
            output+=(this.numbers[ARR_SIZE-1]+" "); //Last element.

        }else{
            for(int i=1;i<ARR_SIZE;i++)  //if the hideMiddleVasls is false.
            {
                output+=(this.numbers[i]+" ");
            }
        }
        return output;
    }
    /**
     * Accepts a user's guess for the game. Validates that it is either the character 'Y' or 'N'. If it is a valid guess,
     * sets the guess data member to the passed value and returns "true". If it is not valid it does not change
     * the value of guess and returns false.
     *
     * @param guessIn - The player's guess.
     * @return True if the passed guess is valid, false if it is not.
     */
    public boolean validatePlayerGuess(char guessIn)
    {
        if(guessIn=='Y' || guessIn=='N') {  //checking if guess by the user is 'Y' or 'N'.
            this.guess = guessIn;
            return true;
        }else {
            return false;
        }
    }
    /**
     * Checks to see if player's guess was correct, and constructs and returns a String that reports if they are correct or
     * incorrect, and appends the correct sum of the array.
     * @return A String reporting the results of the game.
     */
    public java.lang.String getResult()
    {
         this.getArraySum();
        if(this.arraySum>this.guessTarget)  //checking if the sum of array is greater than the guessTarget.
        {
            if(this.guess=='Y')  //if user enters 'Y' it's correct and we return the following string.
            {
                return "You guessed correctly! The sum was "+this.arraySum+"!";
            }else{
                return "You guessed wrong! The sum was "+this.arraySum+"!";
            }
        }else{ //Complete opposite condition.
            if(this.guess=='Y')
            {
                return "You guessed wrong! The sum was "+this.arraySum+"!";
            }else{
                return "You guessed correctly! The sum was "+this.arraySum+"!";
            }
        }
    }

    /**
     * Retrieves the numbers array. Used for testing, do not change.
     * @return The numbers array.
     */
    public int[] getNumbers()
    {
        return numbers;
    }

    /**
     * Retrieves the sum of the numbers in the array. Used for testing, do not change.
     * @return The value of arraySum.
     */
    public int getArraySum() //returning the sum of the elements of the array.
    {
        for(int i=0;i<ARR_SIZE;i++)
        {
            this.arraySum+=this.numbers[i];
        }
        return arraySum;
    }
}


The Code Used for RamdomGuessGameTest.java:


import java.util.Scanner;

public class RandomGuessGameTest {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        RandGuessGame game = new RandGuessGame(new java.util.Random());
        game.populateArray();
        System.out.println("Player Guess Corretly");
        System.out.println(game.toString());
        while(true)
        {
            System.out.println("Is the number greater than "+250+"?");
            System.out.print("(Y or N): ");
            char guess = scanner.next().charAt(0);
            if(game.validatePlayerGuess(guess))
            {
                System.out.println(game.getResult());
                break;
            }
        }
        game.toggleHidden();
        System.out.println(game.toString());
    }
}