Having trouble calling a method to edit a string from another class in java

I've got a simple java program that is supposed to take the specified characters in a string and print them back out to the user by doing everything within a secondary method in a secondary class while taking input from the user in the first class.

The problem that I'm having is that when I try to invoke the secondary method in my main method, I get an error that says "The method copy(String) is unidentified for my main method.

My code for the main method is:

    System.out.println("Copying - Enter a string");
            String currentString = input.next();
            System.out.println("The current string is: " + currentString);
            System.out.println("Enter the starting position");
            int startPosition = input.nextInt();
            System.out.println("Enter one past the ending position");
            int onePastLastPosition = input.nextInt();
            System.out.println("The new string is: " + copy(currentString));

And for the copy method is:

public static String copy(String currentString, int startPosition, int onePastLastPosition) { 
        currentString = currentString.substring(startPosition, onePastLastPosition); 
        return currentString;
    }

So for example, what the code is supposed to do, is if I input a string "abcd", it returns back to me "bc", but the system gets hung up on the last line in the first method. Any help with understanding where I went wrong, and how to fix it in the future would be much appreciated.