How to create error message when negative number is entered in Java factorial

I need to modify this code so that and error message is displayed when a negative number is entered. I know and else statement has to fit in I just can figure out where.

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public static void numberFactorial() {  

    System.out.println("Option 2 selected, enter a number: "); 
    int number = sc.nextInt(); 

    System.out.println("The factorial is: " + number + " ");  


    for (int i = 1; i <= number; i++) 
   {
        factorial *= i;


        if ((number - 1) > 0)   
        {
            System.out.print("x" + (number - i) + " ");

        }

        System.out.println("=" + factorial); 


    }
}

This is the pseudo code I've to follow, I just can't figure out where I've been going wrong. If anyone could help me it would be greatly appreciated.

numberFactorial()

3.2.1 Prompt for number to perform calculation

3.2.2 assign number to variable from scanner in.

3.2.3

3.2.4 if number greater than zero

3.2.5 initialise for loop setting i to 1

3.2.6 loop for i is less than or equal to number

3.2.7 calculate factorial (factorial * i)

3.2.8 if( number – i is greater than zero)

3.2.9 print output (“x ” + “ ” + (number-1)+ “ ”) end if end loop

3.2.10 print factorial else

3.2.11 print message “Enter a positive whole number greater than 0”