Incompatible type double string
===

Why would purchase be an incompatible type for scan.next()? 
(I am trying to get the user input for purchase and tendered, and then use a method to calculate the change).





       public static void makeChange() //one method of a class
       {
       
          double purchase;
          double tendered;

          Scanner scan = new Scanner (System.in);
       
          System.out.println ("How much was the Purchase?");
          purchase = scan.next(); //why would this be an incompatible type?
          System.out.println ("Amount Tendered"); 
          tendered = scan.next();
      
      
          System.out.println("Processing Transaction");
          int ch[] = cd.makeChange(purchase, tendered);
 
               .... continued