User input only numbers, not text in Java

Though your program works for valid inputs, you can make it robust by checking for invalid ones like non-numbers where a number is expected. Your program crashes for a reason: when a user inputs a string, not a number, in this line:

numberCups = scnr.nextFloat();

... then the method nextFloat() will raise an exception, a NumberFormatException to be precise. The Java interpreter cannot handle this exception - it doesn't know what to do when this (valid) situation arises. There is something you can do about that:

do {
  bool validInput = true;
  try {
    numberCups = scnr.nextFloat();
  }
  catch(NumberFormatException ex) {
    validInput = false;
    System.out.println("Please enter a number.");
  }
} while(!validInput);

Now, Java will try to execute nextFloat, and if it fails with a NumberFormatException, it executes the catch block. This gives you a chance to tell the user that their input was wrong. I've put everything in a loop so that when the exception arises, the loop simply runs again until a valid number is input. Note that if the exception does not arise, then the catch block is never executed.

It is good practice to wrap code where an expected error may occur in such a try block in order to handle the situation without unnecessarily crashing the program. Note that there are many types of Exceptions. You should catch the one you expect may happen.

Ref : Only allow input of integers with java scanner

 boolean testing = false;
 String pos = "";
 while(true)
 {
 testing = false;   
 Scanner sc = new Scanner(System.in);
 System.out.println("Enter the integer value.... ");
 pos = sc.next();
 for(int i=0; i<pos.length();i++)
 {
     if(!Character.isDigit(pos.charAt(i)))
         testing = true;
 }
 if(testing == true)
 {
     System.out.print("Enter only numbers..   ");
     continue;
 }

 else
 {
     int key = Integer.parseInt(pos);
     // Your code here....
     break;
 }

You could change nextFloat() and nextInt() for nextLine(), then try to convert them to Integer or Float inside a try-catch block using Integer.parseInt() and Float.parseFloat().

The best you could do is as @ayrton said, use scnr.nextLine() instead of next() or nextFloat(). you can always use the Integer.parseInt() method from Integer class to convert the string into a Number.

Hope this helps.