I can`t meet the secound requirement.

while(!isExit)
        {
            if(keybord.hasNextInt())
            {
                a = keybord.nextInt();
                b = keybord.nextInt();
                c = keybord.nextInt();
                d = keybord.nextInt();
                sum = a; sum = sum + b; sum = sum + c; sum = sum + d;

            }
            else if(keybord.hasNextLine())
            {
                String password = keybord.nextLine();
                isExit = password.equals("ENTER");
            }
        }

You don't need 4 variables (a,b,c,d) just because you have 4 integers to enter. You only need 1 variable or even better, no variable at all for "nextInt" since you don't need to know what "a" was after the program is complete, you only need "sum". This code also results in an error ( which I explained in my last line )

while(!isExit)
        {
            if(keybord.hasNextInt())
            {
                sum += keybord.nextInt();
            }
            else if(keybord.hasNextLine())
            {
                String password = keybord.nextLine();
                isExit = password.equals("ENTER");
            }
        }

Quite important to know this because 1. You save memory and reduce code redundancy. ( removed a,b,c,d variables ) 2. You improve code readability and reduce complexity. ( removed the 3 "nextInt" lines ) 3. You display understanding of logic. ( you don't need to save a,b,c,d.. task asked for "sum" only ) All these will come in handy when you are interviewing for any tech position so it's better to know it now and practice it. Lastly, to answer your question, "nextInt()" method returns "NoSuchElementException" when you are trying to read something that isn't a integer. So if you enter 3 integers, this line: d = keybord.nextInt(); throws an error, that is why you are failing the requirement.

This program doesn't work for any case other than when the user enters 4 integers and then "ENTER". I should be able to get the correct answer if I entered 2 integers and "ENTER", or 5 integers and "ENTER", or even 1000 integers and then "ENTER"