Java parsing multiple files

You can change the scope for those variables by declaring them at the start of the main method.

public static void main(String[] args) {
        Customer customer = null;
        RollerCoaster rollerCoaster = null;

        try {
            File Attrationfile = new File("attractions.txt");
            Scanner attractionscanner = null;
            attractionscanner = new Scanner(Attrationfile);
            while (attractionscanner.hasNext()) {
            String nextline = attractionscanner.nextLine();
            String[] Attractioncomponents = nextline.split("@");

                String ridename =Attractioncomponents[0];
                int price = Integer.parseInt(Attractioncomponents[1]);
                String type = Attractioncomponents[2];
                int unknown = Integer.parseInt(Attractioncomponents[3]) ;
                double speed = Attractioncomponents.length <= 4 ? 0 :
                Double.parseDouble(Attractioncomponents[4]);

                rollerCoaster = new RollerCoaster(ridename, price , unknown, speed);

            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

        try {
             File Customerfile = new File("customers.txt");
             Scanner  Customerscanner = new Scanner(Customerfile);
             while (Customerscanner.hasNext()) {
             String nextline = Customerscanner.nextLine();
             String[] Customercomponents = nextline.split("#");

                int accountnumber =Integer.parseInt(Customercomponents[0]);
                String name = Customercomponents[1];
                int age = Integer.parseInt(Customercomponents[2]) ;
                int balance = Integer.parseInt(Customercomponents[3]) ;
                String discount = Customercomponents.length <= 4 ? String.valueOf(0) :
                        Customercomponents[4];
                customer= new Customer(accountnumber,name , age , balance, discount);


    }

       } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

Welcome to SO! As Hovercraft pointed out, the objects are declared within the scope of the loop, meaning you can't access them outside of it as you noticed. Also, they are overwritten on every iteration, since you declare and initialize the object on every pass. Consider using an ArrayList like so (here just for the customers):

ArrayList<Customer> customerList = new ArrayList<>();
try {
    while (customerScanner.hasNext()) {
        // ...
        customerList.add(new Customer(accountnumber,name, age, balance, discount));
    }
} catch (...) {
    // ...
}

Here's the doc for the ArrayList.

<T> is a generic type, which for you means that you can have an ArrayList<Customer>, ArrayList<RollerCoaster>, ArrayList<String> ...

Sidenote: By convention, variable names start with a lowercase letter, like Scanner customerScanner instead of Scanner Customerscanner.

Is it a question of scope? Try to declare an object outside the body of the loop. Because in Java, the brace is a scope. The more nested braces, the smaller the scope. You can try to declare the objects you need to call in the external scope in the same or larger scope

    String type = null;
    RollerCoaster rollerCoaster = null;
    while (attractionscanner.hasNext()) {
        String nextline = attractionscanner.nextLine();
        String[] Attractioncomponents = nextline.split("@");
        String ridename =Attractioncomponents[0];
        int price = Integer.parseInt(Attractioncomponents[1]);
        type = Attractioncomponents[2];
        int unknown = Integer.parseInt(Attractioncomponents[3]) ;
        double speed = Attractioncomponents.length <= 4 ? 0 :
        Double.parseDouble(Attractioncomponents[4]);
        rollerCoaster = new RollerCoaster(ridename, price , unknown, speed);

    }